1 /* 2 * Copyright (c) 2008, 2017, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang.invoke; 27 28 import sun.invoke.util.VerifyAccess; 29 import sun.invoke.util.Wrapper; 30 import sun.reflect.Reflection; 31 32 import java.lang.reflect.*; 33 import java.nio.ByteOrder; 34 import java.nio.charset.Charset; 35 import java.util.Collections; 36 import java.util.HashMap; 37 import java.util.List; 38 import java.util.Arrays; 39 import java.util.ArrayList; 40 import java.util.Iterator; 41 import java.util.Map; 42 import java.util.Objects; 43 import java.util.stream.Collectors; 44 import java.util.stream.Stream; 45 import jdk.internal.vm.annotation.Stable; 46 47 import static java.lang.invoke.MethodHandleStatics.*; 48 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException; 49 import static java.lang.invoke.MethodType.methodType; 50 51 /** 52 * This class consists exclusively of static methods that operate on or return 53 * method handles. They fall into several categories: 54 * <ul> 55 * <li>Lookup methods which help create method handles for methods and fields. 56 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones. 57 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns. 58 * </ul> 59 * <p> 60 * @author John Rose, JSR 292 EG 61 * @since 1.7 62 */ 63 public class MethodHandles { 64 MethodHandles()65 private MethodHandles() { } // do not instantiate 66 67 // Android-changed: We do not use MemberName / MethodHandleImpl. 68 // 69 // private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory(); 70 // static { MethodHandleImpl.initStatics(); } 71 // See IMPL_LOOKUP below. 72 73 //// Method handle creation from ordinary methods. 74 75 /** 76 * Returns a {@link Lookup lookup object} with 77 * full capabilities to emulate all supported bytecode behaviors of the caller. 78 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller. 79 * Factory methods on the lookup object can create 80 * <a href="MethodHandleInfo.html#directmh">direct method handles</a> 81 * for any member that the caller has access to via bytecodes, 82 * including protected and private fields and methods. 83 * This lookup object is a <em>capability</em> which may be delegated to trusted agents. 84 * Do not store it in place where untrusted code can access it. 85 * <p> 86 * This method is caller sensitive, which means that it may return different 87 * values to different callers. 88 * <p> 89 * For any given caller class {@code C}, the lookup object returned by this call 90 * has equivalent capabilities to any lookup object 91 * supplied by the JVM to the bootstrap method of an 92 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a> 93 * executing in the same caller class {@code C}. 94 * @return a lookup object for the caller of this method, with private access 95 */ 96 // Android-changed: Remove caller sensitive. 97 // @CallerSensitive lookup()98 public static Lookup lookup() { 99 return new Lookup(Reflection.getCallerClass()); 100 } 101 102 /** 103 * Returns a {@link Lookup lookup object} which is trusted minimally. 104 * It can only be used to create method handles to 105 * publicly accessible fields and methods. 106 * <p> 107 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class} 108 * of this lookup object will be {@link java.lang.Object}. 109 * 110 * <p style="font-size:smaller;"> 111 * <em>Discussion:</em> 112 * The lookup class can be changed to any other class {@code C} using an expression of the form 113 * {@link Lookup#in publicLookup().in(C.class)}. 114 * Since all classes have equal access to public names, 115 * such a change would confer no new access rights. 116 * A public lookup object is always subject to 117 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>. 118 * Also, it cannot access 119 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>. 120 * @return a lookup object which is trusted minimally 121 */ publicLookup()122 public static Lookup publicLookup() { 123 return Lookup.PUBLIC_LOOKUP; 124 } 125 126 // Android-removed: Documentation related to the security manager and module checks 127 /** 128 * Returns a {@link Lookup lookup object} with full capabilities to emulate all 129 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc"> 130 * private access</a>, on a target class. 131 * @param targetClass the target class 132 * @param lookup the caller lookup object 133 * @return a lookup object for the target class, with private access 134 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or array class 135 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null} 136 * @throws IllegalAccessException is not thrown on Android 137 * @since 9 138 */ privateLookupIn(Class<?> targetClass, Lookup lookup)139 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException { 140 // Android-removed: SecurityManager calls 141 // SecurityManager sm = System.getSecurityManager(); 142 // if (sm != null) sm.checkPermission(ACCESS_PERMISSION); 143 if (targetClass.isPrimitive()) 144 throw new IllegalArgumentException(targetClass + " is a primitive class"); 145 if (targetClass.isArray()) 146 throw new IllegalArgumentException(targetClass + " is an array class"); 147 // BEGIN Android-removed: There is no module information on Android 148 /** 149 * Module targetModule = targetClass.getModule(); 150 * Module callerModule = lookup.lookupClass().getModule(); 151 * if (!callerModule.canRead(targetModule)) 152 * throw new IllegalAccessException(callerModule + " does not read " + targetModule); 153 * if (targetModule.isNamed()) { 154 * String pn = targetClass.getPackageName(); 155 * assert pn.length() > 0 : "unnamed package cannot be in named module"; 156 * if (!targetModule.isOpen(pn, callerModule)) 157 * throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule); 158 * } 159 * if ((lookup.lookupModes() & Lookup.MODULE) == 0) 160 * throw new IllegalAccessException("lookup does not have MODULE lookup mode"); 161 * if (!callerModule.isNamed() && targetModule.isNamed()) { 162 * IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger(); 163 * if (logger != null) { 164 * logger.logIfOpenedForIllegalAccess(lookup, targetClass); 165 * } 166 * } 167 */ 168 // END Android-removed: There is no module information on Android 169 return new Lookup(targetClass); 170 } 171 172 173 /** 174 * Performs an unchecked "crack" of a 175 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>. 176 * The result is as if the user had obtained a lookup object capable enough 177 * to crack the target method handle, called 178 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect} 179 * on the target to obtain its symbolic reference, and then called 180 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs} 181 * to resolve the symbolic reference to a member. 182 * <p> 183 * If there is a security manager, its {@code checkPermission} method 184 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission. 185 * @param <T> the desired type of the result, either {@link Member} or a subtype 186 * @param target a direct method handle to crack into symbolic reference components 187 * @param expected a class object representing the desired result type {@code T} 188 * @return a reference to the method, constructor, or field object 189 * @exception SecurityException if the caller is not privileged to call {@code setAccessible} 190 * @exception NullPointerException if either argument is {@code null} 191 * @exception IllegalArgumentException if the target is not a direct method handle 192 * @exception ClassCastException if the member is not of the expected type 193 * @since 1.8 194 */ 195 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target)196 reflectAs(Class<T> expected, MethodHandle target) { 197 MethodHandleImpl directTarget = getMethodHandleImpl(target); 198 // Given that this is specified to be an "unchecked" crack, we can directly allocate 199 // a member from the underlying ArtField / Method and bypass all associated access checks. 200 return expected.cast(directTarget.getMemberInternal()); 201 } 202 203 /** 204 * A <em>lookup object</em> is a factory for creating method handles, 205 * when the creation requires access checking. 206 * Method handles do not perform 207 * access checks when they are called, but rather when they are created. 208 * Therefore, method handle access 209 * restrictions must be enforced when a method handle is created. 210 * The caller class against which those restrictions are enforced 211 * is known as the {@linkplain #lookupClass lookup class}. 212 * <p> 213 * A lookup class which needs to create method handles will call 214 * {@link #lookup MethodHandles.lookup} to create a factory for itself. 215 * When the {@code Lookup} factory object is created, the identity of the lookup class is 216 * determined, and securely stored in the {@code Lookup} object. 217 * The lookup class (or its delegates) may then use factory methods 218 * on the {@code Lookup} object to create method handles for access-checked members. 219 * This includes all methods, constructors, and fields which are allowed to the lookup class, 220 * even private ones. 221 * 222 * <h1><a name="lookups"></a>Lookup Factory Methods</h1> 223 * The factory methods on a {@code Lookup} object correspond to all major 224 * use cases for methods, constructors, and fields. 225 * Each method handle created by a factory method is the functional 226 * equivalent of a particular <em>bytecode behavior</em>. 227 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.) 228 * Here is a summary of the correspondence between these factory methods and 229 * the behavior the resulting method handles: 230 * <table border=1 cellpadding=5 summary="lookup method behaviors"> 231 * <tr> 232 * <th><a name="equiv"></a>lookup expression</th> 233 * <th>member</th> 234 * <th>bytecode behavior</th> 235 * </tr> 236 * <tr> 237 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td> 238 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td> 239 * </tr> 240 * <tr> 241 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td> 242 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td> 243 * </tr> 244 * <tr> 245 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td> 246 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td> 247 * </tr> 248 * <tr> 249 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td> 250 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td> 251 * </tr> 252 * <tr> 253 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td> 254 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td> 255 * </tr> 256 * <tr> 257 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td> 258 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td> 259 * </tr> 260 * <tr> 261 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td> 262 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 263 * </tr> 264 * <tr> 265 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td> 266 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td> 267 * </tr> 268 * <tr> 269 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td> 270 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td> 271 * </tr> 272 * <tr> 273 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td> 274 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td> 275 * </tr> 276 * <tr> 277 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td> 278 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td> 279 * </tr> 280 * <tr> 281 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td> 282 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td> 283 * </tr> 284 * <tr> 285 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td> 286 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td> 287 * </tr> 288 * </table> 289 * 290 * Here, the type {@code C} is the class or interface being searched for a member, 291 * documented as a parameter named {@code refc} in the lookup methods. 292 * The method type {@code MT} is composed from the return type {@code T} 293 * and the sequence of argument types {@code A*}. 294 * The constructor also has a sequence of argument types {@code A*} and 295 * is deemed to return the newly-created object of type {@code C}. 296 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}. 297 * The formal parameter {@code this} stands for the self-reference of type {@code C}; 298 * if it is present, it is always the leading argument to the method handle invocation. 299 * (In the case of some {@code protected} members, {@code this} may be 300 * restricted in type to the lookup class; see below.) 301 * The name {@code arg} stands for all the other method handle arguments. 302 * In the code examples for the Core Reflection API, the name {@code thisOrNull} 303 * stands for a null reference if the accessed method or field is static, 304 * and {@code this} otherwise. 305 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand 306 * for reflective objects corresponding to the given members. 307 * <p> 308 * In cases where the given member is of variable arity (i.e., a method or constructor) 309 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}. 310 * In all other cases, the returned method handle will be of fixed arity. 311 * <p style="font-size:smaller;"> 312 * <em>Discussion:</em> 313 * The equivalence between looked-up method handles and underlying 314 * class members and bytecode behaviors 315 * can break down in a few ways: 316 * <ul style="font-size:smaller;"> 317 * <li>If {@code C} is not symbolically accessible from the lookup class's loader, 318 * the lookup can still succeed, even when there is no equivalent 319 * Java expression or bytecoded constant. 320 * <li>Likewise, if {@code T} or {@code MT} 321 * is not symbolically accessible from the lookup class's loader, 322 * the lookup can still succeed. 323 * For example, lookups for {@code MethodHandle.invokeExact} and 324 * {@code MethodHandle.invoke} will always succeed, regardless of requested type. 325 * <li>If there is a security manager installed, it can forbid the lookup 326 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>). 327 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle} 328 * constant is not subject to security manager checks. 329 * <li>If the looked-up method has a 330 * <a href="MethodHandle.html#maxarity">very large arity</a>, 331 * the method handle creation may fail, due to the method handle 332 * type having too many parameters. 333 * </ul> 334 * 335 * <h1><a name="access"></a>Access checking</h1> 336 * Access checks are applied in the factory methods of {@code Lookup}, 337 * when a method handle is created. 338 * This is a key difference from the Core Reflection API, since 339 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 340 * performs access checking against every caller, on every call. 341 * <p> 342 * All access checks start from a {@code Lookup} object, which 343 * compares its recorded lookup class against all requests to 344 * create method handles. 345 * A single {@code Lookup} object can be used to create any number 346 * of access-checked method handles, all checked against a single 347 * lookup class. 348 * <p> 349 * A {@code Lookup} object can be shared with other trusted code, 350 * such as a metaobject protocol. 351 * A shared {@code Lookup} object delegates the capability 352 * to create method handles on private members of the lookup class. 353 * Even if privileged code uses the {@code Lookup} object, 354 * the access checking is confined to the privileges of the 355 * original lookup class. 356 * <p> 357 * A lookup can fail, because 358 * the containing class is not accessible to the lookup class, or 359 * because the desired class member is missing, or because the 360 * desired class member is not accessible to the lookup class, or 361 * because the lookup object is not trusted enough to access the member. 362 * In any of these cases, a {@code ReflectiveOperationException} will be 363 * thrown from the attempted lookup. The exact class will be one of 364 * the following: 365 * <ul> 366 * <li>NoSuchMethodException — if a method is requested but does not exist 367 * <li>NoSuchFieldException — if a field is requested but does not exist 368 * <li>IllegalAccessException — if the member exists but an access check fails 369 * </ul> 370 * <p> 371 * In general, the conditions under which a method handle may be 372 * looked up for a method {@code M} are no more restrictive than the conditions 373 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}. 374 * Where the JVM would raise exceptions like {@code NoSuchMethodError}, 375 * a method handle lookup will generally raise a corresponding 376 * checked exception, such as {@code NoSuchMethodException}. 377 * And the effect of invoking the method handle resulting from the lookup 378 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a> 379 * to executing the compiled, verified, and resolved call to {@code M}. 380 * The same point is true of fields and constructors. 381 * <p style="font-size:smaller;"> 382 * <em>Discussion:</em> 383 * Access checks only apply to named and reflected methods, 384 * constructors, and fields. 385 * Other method handle creation methods, such as 386 * {@link MethodHandle#asType MethodHandle.asType}, 387 * do not require any access checks, and are used 388 * independently of any {@code Lookup} object. 389 * <p> 390 * If the desired member is {@code protected}, the usual JVM rules apply, 391 * including the requirement that the lookup class must be either be in the 392 * same package as the desired member, or must inherit that member. 393 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.) 394 * In addition, if the desired member is a non-static field or method 395 * in a different package, the resulting method handle may only be applied 396 * to objects of the lookup class or one of its subclasses. 397 * This requirement is enforced by narrowing the type of the leading 398 * {@code this} parameter from {@code C} 399 * (which will necessarily be a superclass of the lookup class) 400 * to the lookup class itself. 401 * <p> 402 * The JVM imposes a similar requirement on {@code invokespecial} instruction, 403 * that the receiver argument must match both the resolved method <em>and</em> 404 * the current class. Again, this requirement is enforced by narrowing the 405 * type of the leading parameter to the resulting method handle. 406 * (See the Java Virtual Machine Specification, section 4.10.1.9.) 407 * <p> 408 * The JVM represents constructors and static initializer blocks as internal methods 409 * with special names ({@code "<init>"} and {@code "<clinit>"}). 410 * The internal syntax of invocation instructions allows them to refer to such internal 411 * methods as if they were normal methods, but the JVM bytecode verifier rejects them. 412 * A lookup of such an internal method will produce a {@code NoSuchMethodException}. 413 * <p> 414 * In some cases, access between nested classes is obtained by the Java compiler by creating 415 * an wrapper method to access a private method of another class 416 * in the same top-level declaration. 417 * For example, a nested class {@code C.D} 418 * can access private members within other related classes such as 419 * {@code C}, {@code C.D.E}, or {@code C.B}, 420 * but the Java compiler may need to generate wrapper methods in 421 * those related classes. In such cases, a {@code Lookup} object on 422 * {@code C.E} would be unable to those private members. 423 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method, 424 * which can transform a lookup on {@code C.E} into one on any of those other 425 * classes, without special elevation of privilege. 426 * <p> 427 * The accesses permitted to a given lookup object may be limited, 428 * according to its set of {@link #lookupModes lookupModes}, 429 * to a subset of members normally accessible to the lookup class. 430 * For example, the {@link #publicLookup publicLookup} 431 * method produces a lookup object which is only allowed to access 432 * public members in public classes. 433 * The caller sensitive method {@link #lookup lookup} 434 * produces a lookup object with full capabilities relative to 435 * its caller class, to emulate all supported bytecode behaviors. 436 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object 437 * with fewer access modes than the original lookup object. 438 * 439 * <p style="font-size:smaller;"> 440 * <a name="privacc"></a> 441 * <em>Discussion of private access:</em> 442 * We say that a lookup has <em>private access</em> 443 * if its {@linkplain #lookupModes lookup modes} 444 * include the possibility of accessing {@code private} members. 445 * As documented in the relevant methods elsewhere, 446 * only lookups with private access possess the following capabilities: 447 * <ul style="font-size:smaller;"> 448 * <li>access private fields, methods, and constructors of the lookup class 449 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods, 450 * such as {@code Class.forName} 451 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions 452 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a> 453 * for classes accessible to the lookup class 454 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes 455 * within the same package member 456 * </ul> 457 * <p style="font-size:smaller;"> 458 * Each of these permissions is a consequence of the fact that a lookup object 459 * with private access can be securely traced back to an originating class, 460 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions 461 * can be reliably determined and emulated by method handles. 462 * 463 * <h1><a name="secmgr"></a>Security manager interactions</h1> 464 * Although bytecode instructions can only refer to classes in 465 * a related class loader, this API can search for methods in any 466 * class, as long as a reference to its {@code Class} object is 467 * available. Such cross-loader references are also possible with the 468 * Core Reflection API, and are impossible to bytecode instructions 469 * such as {@code invokestatic} or {@code getfield}. 470 * There is a {@linkplain java.lang.SecurityManager security manager API} 471 * to allow applications to check such cross-loader references. 472 * These checks apply to both the {@code MethodHandles.Lookup} API 473 * and the Core Reflection API 474 * (as found on {@link java.lang.Class Class}). 475 * <p> 476 * If a security manager is present, member lookups are subject to 477 * additional checks. 478 * From one to three calls are made to the security manager. 479 * Any of these calls can refuse access by throwing a 480 * {@link java.lang.SecurityException SecurityException}. 481 * Define {@code smgr} as the security manager, 482 * {@code lookc} as the lookup class of the current lookup object, 483 * {@code refc} as the containing class in which the member 484 * is being sought, and {@code defc} as the class in which the 485 * member is actually defined. 486 * The value {@code lookc} is defined as <em>not present</em> 487 * if the current lookup object does not have 488 * <a href="MethodHandles.Lookup.html#privacc">private access</a>. 489 * The calls are made according to the following rules: 490 * <ul> 491 * <li><b>Step 1:</b> 492 * If {@code lookc} is not present, or if its class loader is not 493 * the same as or an ancestor of the class loader of {@code refc}, 494 * then {@link SecurityManager#checkPackageAccess 495 * smgr.checkPackageAccess(refcPkg)} is called, 496 * where {@code refcPkg} is the package of {@code refc}. 497 * <li><b>Step 2:</b> 498 * If the retrieved member is not public and 499 * {@code lookc} is not present, then 500 * {@link SecurityManager#checkPermission smgr.checkPermission} 501 * with {@code RuntimePermission("accessDeclaredMembers")} is called. 502 * <li><b>Step 3:</b> 503 * If the retrieved member is not public, 504 * and if {@code lookc} is not present, 505 * and if {@code defc} and {@code refc} are different, 506 * then {@link SecurityManager#checkPackageAccess 507 * smgr.checkPackageAccess(defcPkg)} is called, 508 * where {@code defcPkg} is the package of {@code defc}. 509 * </ul> 510 * Security checks are performed after other access checks have passed. 511 * Therefore, the above rules presuppose a member that is public, 512 * or else that is being accessed from a lookup class that has 513 * rights to access the member. 514 * 515 * <h1><a name="callsens"></a>Caller sensitive methods</h1> 516 * A small number of Java methods have a special property called caller sensitivity. 517 * A <em>caller-sensitive</em> method can behave differently depending on the 518 * identity of its immediate caller. 519 * <p> 520 * If a method handle for a caller-sensitive method is requested, 521 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply, 522 * but they take account of the lookup class in a special way. 523 * The resulting method handle behaves as if it were called 524 * from an instruction contained in the lookup class, 525 * so that the caller-sensitive method detects the lookup class. 526 * (By contrast, the invoker of the method handle is disregarded.) 527 * Thus, in the case of caller-sensitive methods, 528 * different lookup classes may give rise to 529 * differently behaving method handles. 530 * <p> 531 * In cases where the lookup object is 532 * {@link #publicLookup publicLookup()}, 533 * or some other lookup object without 534 * <a href="MethodHandles.Lookup.html#privacc">private access</a>, 535 * the lookup class is disregarded. 536 * In such cases, no caller-sensitive method handle can be created, 537 * access is forbidden, and the lookup fails with an 538 * {@code IllegalAccessException}. 539 * <p style="font-size:smaller;"> 540 * <em>Discussion:</em> 541 * For example, the caller-sensitive method 542 * {@link java.lang.Class#forName(String) Class.forName(x)} 543 * can return varying classes or throw varying exceptions, 544 * depending on the class loader of the class that calls it. 545 * A public lookup of {@code Class.forName} will fail, because 546 * there is no reasonable way to determine its bytecode behavior. 547 * <p style="font-size:smaller;"> 548 * If an application caches method handles for broad sharing, 549 * it should use {@code publicLookup()} to create them. 550 * If there is a lookup of {@code Class.forName}, it will fail, 551 * and the application must take appropriate action in that case. 552 * It may be that a later lookup, perhaps during the invocation of a 553 * bootstrap method, can incorporate the specific identity 554 * of the caller, making the method accessible. 555 * <p style="font-size:smaller;"> 556 * The function {@code MethodHandles.lookup} is caller sensitive 557 * so that there can be a secure foundation for lookups. 558 * Nearly all other methods in the JSR 292 API rely on lookup 559 * objects to check access requests. 560 */ 561 // Android-changed: Change link targets from MethodHandles#[public]Lookup to 562 // #[public]Lookup to work around complaints from javadoc. 563 public static final 564 class Lookup { 565 /** The class on behalf of whom the lookup is being performed. */ 566 /* @NonNull */ private final Class<?> lookupClass; 567 568 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */ 569 private final int allowedModes; 570 571 /** A single-bit mask representing {@code public} access, 572 * which may contribute to the result of {@link #lookupModes lookupModes}. 573 * The value, {@code 0x01}, happens to be the same as the value of the 574 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}. 575 */ 576 public static final int PUBLIC = Modifier.PUBLIC; 577 578 /** A single-bit mask representing {@code private} access, 579 * which may contribute to the result of {@link #lookupModes lookupModes}. 580 * The value, {@code 0x02}, happens to be the same as the value of the 581 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}. 582 */ 583 public static final int PRIVATE = Modifier.PRIVATE; 584 585 /** A single-bit mask representing {@code protected} access, 586 * which may contribute to the result of {@link #lookupModes lookupModes}. 587 * The value, {@code 0x04}, happens to be the same as the value of the 588 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}. 589 */ 590 public static final int PROTECTED = Modifier.PROTECTED; 591 592 /** A single-bit mask representing {@code package} access (default access), 593 * which may contribute to the result of {@link #lookupModes lookupModes}. 594 * The value is {@code 0x08}, which does not correspond meaningfully to 595 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 596 */ 597 public static final int PACKAGE = Modifier.STATIC; 598 599 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE); 600 601 // Android-note: Android has no notion of a trusted lookup. If required, such lookups 602 // are performed by the runtime. As a result, we always use lookupClass, which will always 603 // be non-null in our implementation. 604 // 605 // private static final int TRUSTED = -1; 606 fixmods(int mods)607 private static int fixmods(int mods) { 608 mods &= (ALL_MODES - PACKAGE); 609 return (mods != 0) ? mods : PACKAGE; 610 } 611 612 /** Tells which class is performing the lookup. It is this class against 613 * which checks are performed for visibility and access permissions. 614 * <p> 615 * The class implies a maximum level of access permission, 616 * but the permissions may be additionally limited by the bitmask 617 * {@link #lookupModes lookupModes}, which controls whether non-public members 618 * can be accessed. 619 * @return the lookup class, on behalf of which this lookup object finds members 620 */ lookupClass()621 public Class<?> lookupClass() { 622 return lookupClass; 623 } 624 625 /** Tells which access-protection classes of members this lookup object can produce. 626 * The result is a bit-mask of the bits 627 * {@linkplain #PUBLIC PUBLIC (0x01)}, 628 * {@linkplain #PRIVATE PRIVATE (0x02)}, 629 * {@linkplain #PROTECTED PROTECTED (0x04)}, 630 * and {@linkplain #PACKAGE PACKAGE (0x08)}. 631 * <p> 632 * A freshly-created lookup object 633 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} 634 * has all possible bits set, since the caller class can access all its own members. 635 * A lookup object on a new lookup class 636 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object} 637 * may have some mode bits set to zero. 638 * The purpose of this is to restrict access via the new lookup object, 639 * so that it can access only names which can be reached by the original 640 * lookup object, and also by the new lookup class. 641 * @return the lookup modes, which limit the kinds of access performed by this lookup object 642 */ lookupModes()643 public int lookupModes() { 644 return allowedModes & ALL_MODES; 645 } 646 647 /** Embody the current class (the lookupClass) as a lookup class 648 * for method handle creation. 649 * Must be called by from a method in this package, 650 * which in turn is called by a method not in this package. 651 */ Lookup(Class<?> lookupClass)652 Lookup(Class<?> lookupClass) { 653 this(lookupClass, ALL_MODES); 654 // make sure we haven't accidentally picked up a privileged class: 655 checkUnprivilegedlookupClass(lookupClass, ALL_MODES); 656 } 657 Lookup(Class<?> lookupClass, int allowedModes)658 private Lookup(Class<?> lookupClass, int allowedModes) { 659 this.lookupClass = lookupClass; 660 this.allowedModes = allowedModes; 661 } 662 663 /** 664 * Creates a lookup on the specified new lookup class. 665 * The resulting object will report the specified 666 * class as its own {@link #lookupClass lookupClass}. 667 * <p> 668 * However, the resulting {@code Lookup} object is guaranteed 669 * to have no more access capabilities than the original. 670 * In particular, access capabilities can be lost as follows:<ul> 671 * <li>If the new lookup class differs from the old one, 672 * protected members will not be accessible by virtue of inheritance. 673 * (Protected members may continue to be accessible because of package sharing.) 674 * <li>If the new lookup class is in a different package 675 * than the old one, protected and default (package) members will not be accessible. 676 * <li>If the new lookup class is not within the same package member 677 * as the old one, private members will not be accessible. 678 * <li>If the new lookup class is not accessible to the old lookup class, 679 * then no members, not even public members, will be accessible. 680 * (In all other cases, public members will continue to be accessible.) 681 * </ul> 682 * 683 * @param requestedLookupClass the desired lookup class for the new lookup object 684 * @return a lookup object which reports the desired lookup class 685 * @throws NullPointerException if the argument is null 686 */ in(Class<?> requestedLookupClass)687 public Lookup in(Class<?> requestedLookupClass) { 688 requestedLookupClass.getClass(); // null check 689 // Android-changed: There's no notion of a trusted lookup. 690 // if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all 691 // return new Lookup(requestedLookupClass, ALL_MODES); 692 693 if (requestedLookupClass == this.lookupClass) 694 return this; // keep same capabilities 695 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED)); 696 if ((newModes & PACKAGE) != 0 697 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) { 698 newModes &= ~(PACKAGE|PRIVATE); 699 } 700 // Allow nestmate lookups to be created without special privilege: 701 if ((newModes & PRIVATE) != 0 702 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) { 703 newModes &= ~PRIVATE; 704 } 705 if ((newModes & PUBLIC) != 0 706 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) { 707 // The requested class it not accessible from the lookup class. 708 // No permissions. 709 newModes = 0; 710 } 711 checkUnprivilegedlookupClass(requestedLookupClass, newModes); 712 return new Lookup(requestedLookupClass, newModes); 713 } 714 715 // Make sure outer class is initialized first. 716 // 717 // Android-changed: Removed unnecessary reference to IMPL_NAMES. 718 // static { IMPL_NAMES.getClass(); } 719 720 /** Version of lookup which is trusted minimally. 721 * It can only be used to create method handles to 722 * publicly accessible members. 723 */ 724 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC); 725 726 /** Package-private version of lookup which is trusted. */ 727 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, ALL_MODES); 728 checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes)729 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) { 730 String name = lookupClass.getName(); 731 if (name.startsWith("java.lang.invoke.")) 732 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass); 733 734 // For caller-sensitive MethodHandles.lookup() 735 // disallow lookup more restricted packages 736 // 737 // Android-changed: The bootstrap classloader isn't null. 738 if (allowedModes == ALL_MODES && 739 lookupClass.getClassLoader() == Object.class.getClassLoader()) { 740 if ((name.startsWith("java.") 741 && !name.startsWith("java.io.ObjectStreamClass") 742 && !name.startsWith("java.util.concurrent.") 743 && !name.equals("java.lang.Daemons$FinalizerWatchdogDaemon") 744 && !name.equals("java.lang.runtime.ObjectMethods") 745 && !name.equals("java.lang.Thread") 746 && !name.equals("java.util.HashMap") 747 && !name.equals("java.util.HashSet") 748 && !name.equals("java.util.WeakHashMap") 749 && !name.equals("java.lang.runtime.SwitchBootstraps") 750 && !name.startsWith("java.util.stream.")) || 751 (name.startsWith("sun.") 752 && !name.startsWith("sun.invoke.") 753 && !name.equals("sun.reflect.ReflectionFactory"))) { 754 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass); 755 } 756 } 757 } 758 759 /** 760 * Displays the name of the class from which lookups are to be made. 761 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.) 762 * If there are restrictions on the access permitted to this lookup, 763 * this is indicated by adding a suffix to the class name, consisting 764 * of a slash and a keyword. The keyword represents the strongest 765 * allowed access, and is chosen as follows: 766 * <ul> 767 * <li>If no access is allowed, the suffix is "/noaccess". 768 * <li>If only public access is allowed, the suffix is "/public". 769 * <li>If only public and package access are allowed, the suffix is "/package". 770 * <li>If only public, package, and private access are allowed, the suffix is "/private". 771 * </ul> 772 * If none of the above cases apply, it is the case that full 773 * access (public, package, private, and protected) is allowed. 774 * In this case, no suffix is added. 775 * This is true only of an object obtained originally from 776 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}. 777 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in} 778 * always have restricted access, and will display a suffix. 779 * <p> 780 * (It may seem strange that protected access should be 781 * stronger than private access. Viewed independently from 782 * package access, protected access is the first to be lost, 783 * because it requires a direct subclass relationship between 784 * caller and callee.) 785 * @see #in 786 */ 787 @Override toString()788 public String toString() { 789 String cname = lookupClass.getName(); 790 switch (allowedModes) { 791 case 0: // no privileges 792 return cname + "/noaccess"; 793 case PUBLIC: 794 return cname + "/public"; 795 case PUBLIC|PACKAGE: 796 return cname + "/package"; 797 case ALL_MODES & ~PROTECTED: 798 return cname + "/private"; 799 case ALL_MODES: 800 return cname; 801 // Android-changed: No support for TRUSTED callers. 802 // case TRUSTED: 803 // return "/trusted"; // internal only; not exported 804 default: // Should not happen, but it's a bitfield... 805 cname = cname + "/" + Integer.toHexString(allowedModes); 806 assert(false) : cname; 807 return cname; 808 } 809 } 810 811 /** 812 * Produces a method handle for a static method. 813 * The type of the method handle will be that of the method. 814 * (Since static methods do not take receivers, there is no 815 * additional receiver argument inserted into the method handle type, 816 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.) 817 * The method and all its argument types must be accessible to the lookup object. 818 * <p> 819 * The returned method handle will have 820 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 821 * the method's variable arity modifier bit ({@code 0x0080}) is set. 822 * <p> 823 * If the returned method handle is invoked, the method's class will 824 * be initialized, if it has not already been initialized. 825 * <p><b>Example:</b> 826 * <blockquote><pre>{@code 827 import static java.lang.invoke.MethodHandles.*; 828 import static java.lang.invoke.MethodType.*; 829 ... 830 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class, 831 "asList", methodType(List.class, Object[].class)); 832 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString()); 833 * }</pre></blockquote> 834 * @param refc the class from which the method is accessed 835 * @param name the name of the method 836 * @param type the type of the method 837 * @return the desired method handle 838 * @throws NoSuchMethodException if the method does not exist 839 * @throws IllegalAccessException if access checking fails, 840 * or if the method is not {@code static}, 841 * or if the method's variable arity modifier bit 842 * is set and {@code asVarargsCollector} fails 843 * @exception SecurityException if a security manager is present and it 844 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 845 * @throws NullPointerException if any argument is null 846 */ 847 public findStatic(Class<?> refc, String name, MethodType type)848 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 849 Method method = refc.getDeclaredMethod(name, type.ptypes()); 850 final int modifiers = method.getModifiers(); 851 if (!Modifier.isStatic(modifiers)) { 852 throw new IllegalAccessException("Method" + method + " is not static"); 853 } 854 checkReturnType(method, type); 855 checkAccess(refc, method.getDeclaringClass(), modifiers, method.getName()); 856 return createMethodHandle(method, MethodHandle.INVOKE_STATIC, type); 857 } 858 findVirtualForMH(String name, MethodType type)859 private MethodHandle findVirtualForMH(String name, MethodType type) { 860 // these names require special lookups because of the implicit MethodType argument 861 if ("invoke".equals(name)) 862 return invoker(type); 863 if ("invokeExact".equals(name)) 864 return exactInvoker(type); 865 return null; 866 } 867 findVirtualForVH(String name, MethodType type)868 private MethodHandle findVirtualForVH(String name, MethodType type) { 869 VarHandle.AccessMode accessMode; 870 try { 871 accessMode = VarHandle.AccessMode.valueFromMethodName(name); 872 } catch (IllegalArgumentException e) { 873 return null; 874 } 875 return varHandleInvoker(accessMode, type); 876 } 877 createMethodHandle(Method method, int handleKind, MethodType methodType)878 private static MethodHandle createMethodHandle(Method method, int handleKind, 879 MethodType methodType) { 880 MethodHandle mh = new MethodHandleImpl(method.getArtMethod(), handleKind, methodType); 881 if (method.isVarArgs()) { 882 return new Transformers.VarargsCollector(mh); 883 } else { 884 return mh; 885 } 886 } 887 888 /** 889 * Produces a method handle for a virtual method. 890 * The type of the method handle will be that of the method, 891 * with the receiver type (usually {@code refc}) prepended. 892 * The method and all its argument types must be accessible to the lookup object. 893 * <p> 894 * When called, the handle will treat the first argument as a receiver 895 * and dispatch on the receiver's type to determine which method 896 * implementation to enter. 897 * (The dispatching action is identical with that performed by an 898 * {@code invokevirtual} or {@code invokeinterface} instruction.) 899 * <p> 900 * The first argument will be of type {@code refc} if the lookup 901 * class has full privileges to access the member. Otherwise 902 * the member must be {@code protected} and the first argument 903 * will be restricted in type to the lookup class. 904 * <p> 905 * The returned method handle will have 906 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 907 * the method's variable arity modifier bit ({@code 0x0080}) is set. 908 * <p> 909 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual} 910 * instructions and method handles produced by {@code findVirtual}, 911 * if the class is {@code MethodHandle} and the name string is 912 * {@code invokeExact} or {@code invoke}, the resulting 913 * method handle is equivalent to one produced by 914 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or 915 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker} 916 * with the same {@code type} argument. 917 * 918 * <b>Example:</b> 919 * <blockquote><pre>{@code 920 import static java.lang.invoke.MethodHandles.*; 921 import static java.lang.invoke.MethodType.*; 922 ... 923 MethodHandle MH_concat = publicLookup().findVirtual(String.class, 924 "concat", methodType(String.class, String.class)); 925 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class, 926 "hashCode", methodType(int.class)); 927 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class, 928 "hashCode", methodType(int.class)); 929 assertEquals("xy", (String) MH_concat.invokeExact("x", "y")); 930 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy")); 931 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy")); 932 // interface method: 933 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class, 934 "subSequence", methodType(CharSequence.class, int.class, int.class)); 935 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString()); 936 // constructor "internal method" must be accessed differently: 937 MethodType MT_newString = methodType(void.class); //()V for new String() 938 try { assertEquals("impossible", lookup() 939 .findVirtual(String.class, "<init>", MT_newString)); 940 } catch (NoSuchMethodException ex) { } // OK 941 MethodHandle MH_newString = publicLookup() 942 .findConstructor(String.class, MT_newString); 943 assertEquals("", (String) MH_newString.invokeExact()); 944 * }</pre></blockquote> 945 * 946 * @param refc the class or interface from which the method is accessed 947 * @param name the name of the method 948 * @param type the type of the method, with the receiver argument omitted 949 * @return the desired method handle 950 * @throws NoSuchMethodException if the method does not exist 951 * @throws IllegalAccessException if access checking fails, 952 * or if the method is {@code static} 953 * or if the method's variable arity modifier bit 954 * is set and {@code asVarargsCollector} fails 955 * @exception SecurityException if a security manager is present and it 956 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 957 * @throws NullPointerException if any argument is null 958 */ findVirtual(Class<?> refc, String name, MethodType type)959 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 960 // Special case : when we're looking up a virtual method on the MethodHandles class 961 // itself, we can return one of our specialized invokers. 962 if (refc == MethodHandle.class) { 963 MethodHandle mh = findVirtualForMH(name, type); 964 if (mh != null) { 965 return mh; 966 } 967 } else if (refc == VarHandle.class) { 968 // Returns an non-exact invoker. 969 MethodHandle mh = findVirtualForVH(name, type); 970 if (mh != null) { 971 return mh; 972 } 973 } 974 975 Method method = refc.getInstanceMethod(name, type.ptypes()); 976 if (method == null) { 977 // This is pretty ugly and a consequence of the MethodHandles API. We have to throw 978 // an IAE and not an NSME if the method exists but is static (even though the RI's 979 // IAE has a message that says "no such method"). We confine the ugliness and 980 // slowness to the failure case, and allow getInstanceMethod to remain fairly 981 // general. 982 try { 983 Method m = refc.getDeclaredMethod(name, type.ptypes()); 984 if (Modifier.isStatic(m.getModifiers())) { 985 throw new IllegalAccessException("Method" + m + " is static"); 986 } 987 } catch (NoSuchMethodException ignored) { 988 } 989 990 throw new NoSuchMethodException(name + " " + Arrays.toString(type.ptypes())); 991 } 992 checkReturnType(method, type); 993 994 // We have a valid method, perform access checks. 995 checkAccess(refc, method.getDeclaringClass(), method.getModifiers(), method.getName()); 996 997 // Insert the leading reference parameter. 998 MethodType handleType = type.insertParameterTypes(0, refc); 999 int kind = MethodHandle.INVOKE_VIRTUAL; 1000 // This is the same check what Class::FindVirtualMethodForVirtualOrInterface is doing. 1001 // Not doing `isCopied` check as copied methods are not exposed in the reflection APIs. 1002 if (method.getDeclaringClass().isInterface() /* && !method.isCopied() */) { 1003 kind = MethodHandle.INVOKE_INTERFACE; 1004 } 1005 return createMethodHandle(method, kind, handleType); 1006 } 1007 1008 /** 1009 * Produces a method handle which creates an object and initializes it, using 1010 * the constructor of the specified type. 1011 * The parameter types of the method handle will be those of the constructor, 1012 * while the return type will be a reference to the constructor's class. 1013 * The constructor and all its argument types must be accessible to the lookup object. 1014 * <p> 1015 * The requested type must have a return type of {@code void}. 1016 * (This is consistent with the JVM's treatment of constructor type descriptors.) 1017 * <p> 1018 * The returned method handle will have 1019 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1020 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 1021 * <p> 1022 * If the returned method handle is invoked, the constructor's class will 1023 * be initialized, if it has not already been initialized. 1024 * <p><b>Example:</b> 1025 * <blockquote><pre>{@code 1026 import static java.lang.invoke.MethodHandles.*; 1027 import static java.lang.invoke.MethodType.*; 1028 ... 1029 MethodHandle MH_newArrayList = publicLookup().findConstructor( 1030 ArrayList.class, methodType(void.class, Collection.class)); 1031 Collection orig = Arrays.asList("x", "y"); 1032 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig); 1033 assert(orig != copy); 1034 assertEquals(orig, copy); 1035 // a variable-arity constructor: 1036 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor( 1037 ProcessBuilder.class, methodType(void.class, String[].class)); 1038 ProcessBuilder pb = (ProcessBuilder) 1039 MH_newProcessBuilder.invoke("x", "y", "z"); 1040 assertEquals("[x, y, z]", pb.command().toString()); 1041 * }</pre></blockquote> 1042 * @param refc the class or interface from which the method is accessed 1043 * @param type the type of the method, with the receiver argument omitted, and a void return type 1044 * @return the desired method handle 1045 * @throws NoSuchMethodException if the constructor does not exist 1046 * @throws IllegalAccessException if access checking fails 1047 * or if the method's variable arity modifier bit 1048 * is set and {@code asVarargsCollector} fails 1049 * @exception SecurityException if a security manager is present and it 1050 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1051 * @throws NullPointerException if any argument is null 1052 */ findConstructor(Class<?> refc, MethodType type)1053 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException { 1054 if (refc.isArray()) { 1055 throw new NoSuchMethodException("no constructor for array class: " + refc.getName()); 1056 } 1057 // The queried |type| is (PT1,PT2,..)V 1058 Constructor constructor = refc.getDeclaredConstructor(type.ptypes()); 1059 if (constructor == null) { 1060 throw new NoSuchMethodException( 1061 "No constructor for " + constructor.getDeclaringClass() + " matching " + type); 1062 } 1063 checkAccess(refc, constructor.getDeclaringClass(), constructor.getModifiers(), 1064 constructor.getName()); 1065 1066 return createMethodHandleForConstructor(constructor); 1067 } 1068 1069 // BEGIN Android-added: Add findClass(String) from OpenJDK 17. http://b/270028670 1070 // TODO: Unhide this method. 1071 /** 1072 * Looks up a class by name from the lookup context defined by this {@code Lookup} object, 1073 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction. 1074 * Such a resolution, as specified in JVMS 5.4.3.1 section, attempts to locate and load the class, 1075 * and then determines whether the class is accessible to this lookup object. 1076 * <p> 1077 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, 1078 * its class loader, and the {@linkplain #lookupModes() lookup modes}. 1079 * 1080 * @param targetName the fully qualified name of the class to be looked up. 1081 * @return the requested class. 1082 * @throws SecurityException if a security manager is present and it 1083 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1084 * @throws LinkageError if the linkage fails 1085 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader. 1086 * @throws IllegalAccessException if the class is not accessible, using the allowed access 1087 * modes. 1088 * @throws NullPointerException if {@code targetName} is null 1089 * @since 9 1090 * @jvms 5.4.3.1 Class and Interface Resolution 1091 * @hide 1092 */ findClass(String targetName)1093 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException { 1094 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader()); 1095 return accessClass(targetClass); 1096 } 1097 // END Android-added: Add findClass(String) from OpenJDK 17. http://b/270028670 1098 1099 // BEGIN Android-added: mapping from String constructors to StringFactory methods. 1100 private static final Map<Constructor<String>, Method> STRING_TO_STRING_FACTORY = 1101 buildMapping(); 1102 buildMapping()1103 private static Map<Constructor<String>, Method> buildMapping() { 1104 // If system image is not provided, during bootstrap time 1105 // String.class.getDeclaringConstructor will succeeded, but j.l.r.Constructor might 1106 // not be initialized yet. Hence initializing it explicitly here. 1107 try { 1108 Class.forName("java.lang.reflect.Constructor"); 1109 } catch (Exception e) { 1110 throw new InternalError("Failed to initialize Constructor class", e); 1111 } 1112 1113 Map<Constructor<String>, Method> mapping = new HashMap<>(); 1114 Map<List<Class<?>>, String> signatureAndName = new HashMap<>(); 1115 // Intentionally not using ImmutableCollections (List.of, Map.copyOf) below. 1116 // ImmutableCollections' static initializer calls System.nanoTime and adding its 1117 // implementation to UnstartedRuntime leads to Math.RandomNumberGeneratorHolder 1118 // initialization in the system image effectively making it deterministic. 1119 signatureAndName.put(Arrays.asList(), "newEmptyString"); 1120 signatureAndName.put(Arrays.asList(byte[].class),"newStringFromBytes"); 1121 signatureAndName.put(Arrays.asList(byte[].class, byte.class), "newStringFromBytes"); 1122 signatureAndName.put(Arrays.asList(byte[].class, int.class), "newStringFromBytes"); 1123 signatureAndName.put( 1124 Arrays.asList(byte[].class, int.class, int.class), "newStringFromBytes"); 1125 signatureAndName.put( 1126 Arrays.asList(byte[].class, int.class, int.class, int.class), 1127 "newStringFromBytes"); 1128 signatureAndName.put( 1129 Arrays.asList(byte[].class, int.class, int.class, String.class), 1130 "newStringFromBytes"); 1131 signatureAndName.put(Arrays.asList(byte[].class, String.class), "newStringFromBytes"); 1132 signatureAndName.put( 1133 Arrays.asList(byte[].class, int.class, int.class, Charset.class), 1134 "newStringFromBytes"); 1135 signatureAndName.put(Arrays.asList(byte[].class, Charset.class), "newStringFromBytes"); 1136 signatureAndName.put(Arrays.asList(char[].class), "newStringFromChars"); 1137 signatureAndName.put( 1138 Arrays.asList(char[].class, int.class, int.class), "newStringFromChars"); 1139 signatureAndName.put( 1140 Arrays.asList(int.class, int.class, char[].class), "newStringFromChars"); 1141 signatureAndName.put(Arrays.asList(String.class), "newStringFromString"); 1142 signatureAndName.put(Arrays.asList(StringBuffer.class), "newStringFromStringBuffer"); 1143 signatureAndName.put( 1144 Arrays.asList(int[].class, int.class, int.class), "newStringFromCodePoints"); 1145 signatureAndName.put(Arrays.asList(StringBuilder.class), "newStringFromStringBuilder"); 1146 1147 for (var entry : signatureAndName.entrySet()) { 1148 List<Class<?>> types = entry.getKey(); 1149 String name = entry.getValue(); 1150 try { 1151 Constructor<String> stringConstructor = 1152 String.class.getDeclaredConstructor( 1153 types.toArray(new Class<?>[0])); 1154 Method factoryMethod = 1155 StringFactory.class.getDeclaredMethod( 1156 name, types.toArray(new Class<?>[0])); 1157 if (mapping.put(stringConstructor, factoryMethod) != null) { 1158 throw new InternalError("Attempt to remap " + stringConstructor); 1159 } 1160 } catch (NoSuchMethodException nsme) { 1161 throw new InternalError(nsme); 1162 } 1163 } 1164 1165 return Collections.unmodifiableMap(mapping); 1166 } 1167 findStringFactoryMethod(Constructor<String> constructor)1168 private static Method findStringFactoryMethod(Constructor<String> constructor) { 1169 return Objects.requireNonNull(STRING_TO_STRING_FACTORY.get(constructor), 1170 "No mapping for " + constructor); 1171 } 1172 // END Android-added: mapping from String constructors to StringFactory methods. 1173 createMethodHandleForConstructor(Constructor constructor)1174 private MethodHandle createMethodHandleForConstructor(Constructor constructor) { 1175 Class<?> refc = constructor.getDeclaringClass(); 1176 MethodType constructorType = 1177 MethodType.methodType(refc, constructor.getParameterTypes()); 1178 MethodHandle mh; 1179 if (refc == String.class) { 1180 // String constructors have optimized StringFactory methods 1181 // that matches returned type. These factory methods combine the 1182 // memory allocation and initialization calls for String objects. 1183 mh = new MethodHandleImpl(findStringFactoryMethod(constructor).getArtMethod(), 1184 MethodHandle.INVOKE_STATIC, constructorType); 1185 } else { 1186 // Constructors for all other classes use a Construct transformer to perform 1187 // their memory allocation and call to <init>. 1188 MethodType initType = initMethodType(constructorType); 1189 MethodHandle initHandle = new MethodHandleImpl( 1190 constructor.getArtMethod(), MethodHandle.INVOKE_DIRECT, initType); 1191 mh = new Transformers.Construct(initHandle, constructorType); 1192 } 1193 1194 if (constructor.isVarArgs()) { 1195 mh = new Transformers.VarargsCollector(mh); 1196 } 1197 return mh; 1198 } 1199 initMethodType(MethodType constructorType)1200 private static MethodType initMethodType(MethodType constructorType) { 1201 // Returns a MethodType appropriate for class <init> 1202 // methods. Constructor MethodTypes have the form 1203 // (PT1,PT2,...)C and class <init> MethodTypes have the 1204 // form (C,PT1,PT2,...)V. 1205 assert constructorType.rtype() != void.class; 1206 1207 // Insert constructorType C as the first parameter type in 1208 // the MethodType for <init>. 1209 Class<?> [] initPtypes = new Class<?> [constructorType.ptypes().length + 1]; 1210 initPtypes[0] = constructorType.rtype(); 1211 System.arraycopy(constructorType.ptypes(), 0, initPtypes, 1, 1212 constructorType.ptypes().length); 1213 1214 // Set the return type for the <init> MethodType to be void. 1215 return MethodType.methodType(void.class, initPtypes); 1216 } 1217 1218 // BEGIN Android-added: Add accessClass(Class) from OpenJDK 17. http://b/270028670 1219 /* 1220 * Returns IllegalAccessException due to access violation to the given targetClass. 1221 * 1222 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized} 1223 * which verifies access to a class rather a member. 1224 */ makeAccessException(Class<?> targetClass)1225 private IllegalAccessException makeAccessException(Class<?> targetClass) { 1226 String message = "access violation: "+ targetClass; 1227 if (this == MethodHandles.publicLookup()) { 1228 message += ", from public Lookup"; 1229 } else { 1230 // Android-changed: Remove unsupported module name. 1231 // Module m = lookupClass().getModule(); 1232 // message += ", from " + lookupClass() + " (" + m + ")"; 1233 message += ", from " + lookupClass(); 1234 // Android-removed: Remove prevLookupClass until supported by Lookup in OpenJDK 17. 1235 // if (prevLookupClass != null) { 1236 // message += ", previous lookup " + 1237 // prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")"; 1238 // } 1239 } 1240 return new IllegalAccessException(message); 1241 } 1242 1243 // TODO: Unhide this method. 1244 /** 1245 * Determines if a class can be accessed from the lookup context defined by 1246 * this {@code Lookup} object. The static initializer of the class is not run. 1247 * If {@code targetClass} is an array class, {@code targetClass} is accessible 1248 * if the element type of the array class is accessible. Otherwise, 1249 * {@code targetClass} is determined as accessible as follows. 1250 * 1251 * <p> 1252 * If {@code targetClass} is in the same module as the lookup class, 1253 * the lookup class is {@code LC} in module {@code M1} and 1254 * the previous lookup class is in module {@code M0} or 1255 * {@code null} if not present, 1256 * {@code targetClass} is accessible if and only if one of the following is true: 1257 * <ul> 1258 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is 1259 * {@code LC} or other class in the same nest of {@code LC}.</li> 1260 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is 1261 * in the same runtime package of {@code LC}.</li> 1262 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is 1263 * a public type in {@code M1}.</li> 1264 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is 1265 * a public type in a package exported by {@code M1} to at least {@code M0} 1266 * if the previous lookup class is present; otherwise, {@code targetClass} 1267 * is a public type in a package exported by {@code M1} unconditionally.</li> 1268 * </ul> 1269 * 1270 * <p> 1271 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup 1272 * can access public types in all modules when the type is in a package 1273 * that is exported unconditionally. 1274 * <p> 1275 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass}, 1276 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass} 1277 * is inaccessible. 1278 * <p> 1279 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class}, 1280 * {@code M1} is the module containing {@code lookupClass} and 1281 * {@code M2} is the module containing {@code targetClass}, 1282 * then {@code targetClass} is accessible if and only if 1283 * <ul> 1284 * <li>{@code M1} reads {@code M2}, and 1285 * <li>{@code targetClass} is public and in a package exported by 1286 * {@code M2} at least to {@code M1}. 1287 * </ul> 1288 * <p> 1289 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class}, 1290 * {@code M1} and {@code M2} are as before, and {@code M0} is the module 1291 * containing the previous lookup class, then {@code targetClass} is accessible 1292 * if and only if one of the following is true: 1293 * <ul> 1294 * <li>{@code targetClass} is in {@code M0} and {@code M1} 1295 * {@linkplain Module#reads reads} {@code M0} and the type is 1296 * in a package that is exported to at least {@code M1}. 1297 * <li>{@code targetClass} is in {@code M1} and {@code M0} 1298 * {@linkplain Module#reads reads} {@code M1} and the type is 1299 * in a package that is exported to at least {@code M0}. 1300 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0} 1301 * and {@code M1} reads {@code M2} and the type is in a package 1302 * that is exported to at least both {@code M0} and {@code M2}. 1303 * </ul> 1304 * <p> 1305 * Otherwise, {@code targetClass} is not accessible. 1306 * 1307 * @param targetClass the class to be access-checked 1308 * @return the class that has been access-checked 1309 * @throws IllegalAccessException if the class is not accessible from the lookup class 1310 * and previous lookup class, if present, using the allowed access modes. 1311 * @throws SecurityException if a security manager is present and it 1312 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1313 * @throws NullPointerException if {@code targetClass} is {@code null} 1314 * @since 9 1315 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1316 * @hide 1317 */ accessClass(Class<?> targetClass)1318 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException { 1319 if (!isClassAccessible(targetClass)) { 1320 throw makeAccessException(targetClass); 1321 } 1322 // Android-removed: SecurityManager is unnecessary on Android. 1323 // checkSecurityManager(targetClass); 1324 return targetClass; 1325 } 1326 isClassAccessible(Class<?> refc)1327 boolean isClassAccessible(Class<?> refc) { 1328 Objects.requireNonNull(refc); 1329 Class<?> caller = lookupClassOrNull(); 1330 Class<?> type = refc; 1331 while (type.isArray()) { 1332 type = type.getComponentType(); 1333 } 1334 // Android-removed: Remove prevLookupClass until supported by Lookup in OpenJDK 17. 1335 // return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes); 1336 return caller == null || VerifyAccess.isClassAccessible(type, caller, allowedModes); 1337 } 1338 1339 // This is just for calling out to MethodHandleImpl. lookupClassOrNull()1340 private Class<?> lookupClassOrNull() { 1341 // Android-changed: Android always returns lookupClass and has no concept of TRUSTED. 1342 // return (allowedModes == TRUSTED) ? null : lookupClass; 1343 return lookupClass; 1344 } 1345 // END Android-added: Add accessClass(Class) from OpenJDK 17. http://b/270028670 1346 1347 /** 1348 * Produces an early-bound method handle for a virtual method. 1349 * It will bypass checks for overriding methods on the receiver, 1350 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 1351 * instruction from within the explicitly specified {@code specialCaller}. 1352 * The type of the method handle will be that of the method, 1353 * with a suitably restricted receiver type prepended. 1354 * (The receiver type will be {@code specialCaller} or a subtype.) 1355 * The method and all its argument types must be accessible 1356 * to the lookup object. 1357 * <p> 1358 * Before method resolution, 1359 * if the explicitly specified caller class is not identical with the 1360 * lookup class, or if this lookup object does not have 1361 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 1362 * privileges, the access fails. 1363 * <p> 1364 * The returned method handle will have 1365 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1366 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1367 * <p style="font-size:smaller;"> 1368 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API, 1369 * even though the {@code invokespecial} instruction can refer to them 1370 * in special circumstances. Use {@link #findConstructor findConstructor} 1371 * to access instance initialization methods in a safe manner.)</em> 1372 * <p><b>Example:</b> 1373 * <blockquote><pre>{@code 1374 import static java.lang.invoke.MethodHandles.*; 1375 import static java.lang.invoke.MethodType.*; 1376 ... 1377 static class Listie extends ArrayList { 1378 public String toString() { return "[wee Listie]"; } 1379 static Lookup lookup() { return MethodHandles.lookup(); } 1380 } 1381 ... 1382 // no access to constructor via invokeSpecial: 1383 MethodHandle MH_newListie = Listie.lookup() 1384 .findConstructor(Listie.class, methodType(void.class)); 1385 Listie l = (Listie) MH_newListie.invokeExact(); 1386 try { assertEquals("impossible", Listie.lookup().findSpecial( 1387 Listie.class, "<init>", methodType(void.class), Listie.class)); 1388 } catch (NoSuchMethodException ex) { } // OK 1389 // access to super and self methods via invokeSpecial: 1390 MethodHandle MH_super = Listie.lookup().findSpecial( 1391 ArrayList.class, "toString" , methodType(String.class), Listie.class); 1392 MethodHandle MH_this = Listie.lookup().findSpecial( 1393 Listie.class, "toString" , methodType(String.class), Listie.class); 1394 MethodHandle MH_duper = Listie.lookup().findSpecial( 1395 Object.class, "toString" , methodType(String.class), Listie.class); 1396 assertEquals("[]", (String) MH_super.invokeExact(l)); 1397 assertEquals(""+l, (String) MH_this.invokeExact(l)); 1398 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method 1399 try { assertEquals("inaccessible", Listie.lookup().findSpecial( 1400 String.class, "toString", methodType(String.class), Listie.class)); 1401 } catch (IllegalAccessException ex) { } // OK 1402 Listie subl = new Listie() { public String toString() { return "[subclass]"; } }; 1403 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method 1404 * }</pre></blockquote> 1405 * 1406 * @param refc the class or interface from which the method is accessed 1407 * @param name the name of the method (which must not be "<init>") 1408 * @param type the type of the method, with the receiver argument omitted 1409 * @param specialCaller the proposed calling class to perform the {@code invokespecial} 1410 * @return the desired method handle 1411 * @throws NoSuchMethodException if the method does not exist 1412 * @throws IllegalAccessException if access checking fails 1413 * or if the method's variable arity modifier bit 1414 * is set and {@code asVarargsCollector} fails 1415 * @exception SecurityException if a security manager is present and it 1416 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1417 * @throws NullPointerException if any argument is null 1418 */ findSpecial(Class<?> refc, String name, MethodType type, Class<?> specialCaller)1419 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type, 1420 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException { 1421 if (specialCaller == null) { 1422 throw new NullPointerException("specialCaller == null"); 1423 } 1424 1425 if (type == null) { 1426 throw new NullPointerException("type == null"); 1427 } 1428 1429 if (name == null) { 1430 throw new NullPointerException("name == null"); 1431 } 1432 1433 if (refc == null) { 1434 throw new NullPointerException("ref == null"); 1435 } 1436 1437 // Make sure that the special caller is identical to the lookup class or that we have 1438 // private access. 1439 // Android-changed: Also allow access to any interface methods. 1440 checkSpecialCaller(specialCaller, refc); 1441 1442 // Even though constructors are invoked using a "special" invoke, handles to them can't 1443 // be created using findSpecial. Callers must use findConstructor instead. Similarly, 1444 // there is no path for calling static class initializers. 1445 if (name.startsWith("<")) { 1446 throw new NoSuchMethodException(name + " is not a valid method name."); 1447 } 1448 1449 Method method = refc.getDeclaredMethod(name, type.ptypes()); 1450 checkReturnType(method, type); 1451 return findSpecial(method, type, refc, specialCaller); 1452 } 1453 findSpecial(Method method, MethodType type, Class<?> refc, Class<?> specialCaller)1454 private MethodHandle findSpecial(Method method, MethodType type, 1455 Class<?> refc, Class<?> specialCaller) 1456 throws IllegalAccessException { 1457 if (Modifier.isStatic(method.getModifiers())) { 1458 throw new IllegalAccessException("expected a non-static method:" + method); 1459 } 1460 1461 if (Modifier.isPrivate(method.getModifiers())) { 1462 // Since this is a private method, we'll need to also make sure that the 1463 // lookup class is the same as the refering class. We've already checked that 1464 // the specialCaller is the same as the special lookup class, both of these must 1465 // be the same as the declaring class(*) in order to access the private method. 1466 // 1467 // (*) Well, this isn't true for nested classes but OpenJDK doesn't support those 1468 // either. 1469 if (refc != lookupClass()) { 1470 throw new IllegalAccessException("no private access for invokespecial : " 1471 + refc + ", from" + this); 1472 } 1473 1474 // This is a private method, so there's nothing special to do. 1475 MethodType handleType = type.insertParameterTypes(0, refc); 1476 return createMethodHandle(method, MethodHandle.INVOKE_DIRECT, handleType); 1477 } 1478 1479 // This is a public, protected or package-private method, which means we're expecting 1480 // invoke-super semantics. We'll have to restrict the receiver type appropriately on the 1481 // handle once we check that there really is a "super" relationship between them. 1482 if (!method.getDeclaringClass().isAssignableFrom(specialCaller)) { 1483 throw new IllegalAccessException(refc + "is not assignable from " + specialCaller); 1484 } 1485 1486 // Note that we restrict the receiver to "specialCaller" instances. 1487 MethodType handleType = type.insertParameterTypes(0, specialCaller); 1488 return createMethodHandle(method, MethodHandle.INVOKE_SUPER, handleType); 1489 } 1490 1491 /** 1492 * Produces a method handle giving read access to a non-static field. 1493 * The type of the method handle will have a return type of the field's 1494 * value type. 1495 * The method handle's single argument will be the instance containing 1496 * the field. 1497 * Access checking is performed immediately on behalf of the lookup class. 1498 * @param refc the class or interface from which the method is accessed 1499 * @param name the field's name 1500 * @param type the field's type 1501 * @return a method handle which can load values from the field 1502 * @throws NoSuchFieldException if the field does not exist 1503 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 1504 * @exception SecurityException if a security manager is present and it 1505 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1506 * @throws NullPointerException if any argument is null 1507 */ findGetter(Class<?> refc, String name, Class<?> type)1508 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1509 return findAccessor(refc, name, type, MethodHandle.IGET); 1510 } 1511 findAccessor(Class<?> refc, String name, Class<?> type, int kind)1512 private MethodHandle findAccessor(Class<?> refc, String name, Class<?> type, int kind) 1513 throws NoSuchFieldException, IllegalAccessException { 1514 final Field field = findFieldOfType(refc, name, type); 1515 return findAccessor(field, refc, type, kind, true /* performAccessChecks */); 1516 } 1517 findAccessor(Field field, Class<?> refc, Class<?> type, int kind, boolean performAccessChecks)1518 private MethodHandle findAccessor(Field field, Class<?> refc, Class<?> type, int kind, 1519 boolean performAccessChecks) 1520 throws IllegalAccessException { 1521 final boolean isSetterKind = kind == MethodHandle.IPUT || kind == MethodHandle.SPUT; 1522 final boolean isStaticKind = kind == MethodHandle.SGET || kind == MethodHandle.SPUT; 1523 commonFieldChecks(field, refc, type, isStaticKind, performAccessChecks); 1524 if (performAccessChecks) { 1525 final int modifiers = field.getModifiers(); 1526 if (isSetterKind && Modifier.isFinal(modifiers)) { 1527 throw new IllegalAccessException("Field " + field + " is final"); 1528 } 1529 } 1530 1531 final MethodType methodType; 1532 switch (kind) { 1533 case MethodHandle.SGET: 1534 methodType = MethodType.methodType(type); 1535 break; 1536 case MethodHandle.SPUT: 1537 methodType = MethodType.methodType(void.class, type); 1538 break; 1539 case MethodHandle.IGET: 1540 methodType = MethodType.methodType(type, refc); 1541 break; 1542 case MethodHandle.IPUT: 1543 methodType = MethodType.methodType(void.class, refc, type); 1544 break; 1545 default: 1546 throw new IllegalArgumentException("Invalid kind " + kind); 1547 } 1548 return new MethodHandleImpl(field, kind, methodType); 1549 } 1550 1551 /** 1552 * Produces a method handle giving write access to a non-static field. 1553 * The type of the method handle will have a void return type. 1554 * The method handle will take two arguments, the instance containing 1555 * the field, and the value to be stored. 1556 * The second argument will be of the field's value type. 1557 * Access checking is performed immediately on behalf of the lookup class. 1558 * @param refc the class or interface from which the method is accessed 1559 * @param name the field's name 1560 * @param type the field's type 1561 * @return a method handle which can store values into the field 1562 * @throws NoSuchFieldException if the field does not exist 1563 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 1564 * @exception SecurityException if a security manager is present and it 1565 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1566 * @throws NullPointerException if any argument is null 1567 */ findSetter(Class<?> refc, String name, Class<?> type)1568 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1569 return findAccessor(refc, name, type, MethodHandle.IPUT); 1570 } 1571 1572 // BEGIN Android-changed: OpenJDK 9+181 VarHandle API factory method. 1573 /** 1574 * Produces a VarHandle giving access to a non-static field {@code name} 1575 * of type {@code type} declared in a class of type {@code recv}. 1576 * The VarHandle's variable type is {@code type} and it has one 1577 * coordinate type, {@code recv}. 1578 * <p> 1579 * Access checking is performed immediately on behalf of the lookup 1580 * class. 1581 * <p> 1582 * Certain access modes of the returned VarHandle are unsupported under 1583 * the following conditions: 1584 * <ul> 1585 * <li>if the field is declared {@code final}, then the write, atomic 1586 * update, numeric atomic update, and bitwise atomic update access 1587 * modes are unsupported. 1588 * <li>if the field type is anything other than {@code byte}, 1589 * {@code short}, {@code char}, {@code int}, {@code long}, 1590 * {@code float}, or {@code double} then numeric atomic update 1591 * access modes are unsupported. 1592 * <li>if the field type is anything other than {@code boolean}, 1593 * {@code byte}, {@code short}, {@code char}, {@code int} or 1594 * {@code long} then bitwise atomic update access modes are 1595 * unsupported. 1596 * </ul> 1597 * <p> 1598 * If the field is declared {@code volatile} then the returned VarHandle 1599 * will override access to the field (effectively ignore the 1600 * {@code volatile} declaration) in accordance to its specified 1601 * access modes. 1602 * <p> 1603 * If the field type is {@code float} or {@code double} then numeric 1604 * and atomic update access modes compare values using their bitwise 1605 * representation (see {@link Float#floatToRawIntBits} and 1606 * {@link Double#doubleToRawLongBits}, respectively). 1607 * @apiNote 1608 * Bitwise comparison of {@code float} values or {@code double} values, 1609 * as performed by the numeric and atomic update access modes, differ 1610 * from the primitive {@code ==} operator and the {@link Float#equals} 1611 * and {@link Double#equals} methods, specifically with respect to 1612 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 1613 * Care should be taken when performing a compare and set or a compare 1614 * and exchange operation with such values since the operation may 1615 * unexpectedly fail. 1616 * There are many possible NaN values that are considered to be 1617 * {@code NaN} in Java, although no IEEE 754 floating-point operation 1618 * provided by Java can distinguish between them. Operation failure can 1619 * occur if the expected or witness value is a NaN value and it is 1620 * transformed (perhaps in a platform specific manner) into another NaN 1621 * value, and thus has a different bitwise representation (see 1622 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 1623 * details). 1624 * The values {@code -0.0} and {@code +0.0} have different bitwise 1625 * representations but are considered equal when using the primitive 1626 * {@code ==} operator. Operation failure can occur if, for example, a 1627 * numeric algorithm computes an expected value to be say {@code -0.0} 1628 * and previously computed the witness value to be say {@code +0.0}. 1629 * @param recv the receiver class, of type {@code R}, that declares the 1630 * non-static field 1631 * @param name the field's name 1632 * @param type the field's type, of type {@code T} 1633 * @return a VarHandle giving access to non-static fields. 1634 * @throws NoSuchFieldException if the field does not exist 1635 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 1636 * @exception SecurityException if a security manager is present and it 1637 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1638 * @throws NullPointerException if any argument is null 1639 * @since 9 1640 */ findVarHandle(Class<?> recv, String name, Class<?> type)1641 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1642 final Field field = findFieldOfType(recv, name, type); 1643 final boolean isStatic = false; 1644 final boolean performAccessChecks = true; 1645 commonFieldChecks(field, recv, type, isStatic, performAccessChecks); 1646 return FieldVarHandle.create(field); 1647 } 1648 // END Android-changed: OpenJDK 9+181 VarHandle API factory method. 1649 1650 // BEGIN Android-added: Common field resolution and access check methods. findFieldOfType(final Class<?> refc, String name, Class<?> type)1651 private Field findFieldOfType(final Class<?> refc, String name, Class<?> type) 1652 throws NoSuchFieldException { 1653 Field field = null; 1654 1655 // Search refc and super classes for the field. 1656 for (Class<?> cls = refc; cls != null; cls = cls.getSuperclass()) { 1657 try { 1658 field = cls.getDeclaredField(name); 1659 break; 1660 } catch (NoSuchFieldException e) { 1661 } 1662 } 1663 1664 if (field == null) { 1665 // Force failure citing refc. 1666 field = refc.getDeclaredField(name); 1667 } 1668 1669 final Class<?> fieldType = field.getType(); 1670 if (fieldType != type) { 1671 throw new NoSuchFieldException(name); 1672 } 1673 return field; 1674 } 1675 commonFieldChecks(Field field, Class<?> refc, Class<?> type, boolean isStatic, boolean performAccessChecks)1676 private void commonFieldChecks(Field field, Class<?> refc, Class<?> type, 1677 boolean isStatic, boolean performAccessChecks) 1678 throws IllegalAccessException { 1679 final int modifiers = field.getModifiers(); 1680 if (performAccessChecks) { 1681 checkAccess(refc, field.getDeclaringClass(), modifiers, field.getName()); 1682 } 1683 if (Modifier.isStatic(modifiers) != isStatic) { 1684 String reason = "Field " + field + " is " + 1685 (isStatic ? "not " : "") + "static"; 1686 throw new IllegalAccessException(reason); 1687 } 1688 } 1689 // END Android-added: Common field resolution and access check methods. 1690 1691 /** 1692 * Produces a method handle giving read access to a static field. 1693 * The type of the method handle will have a return type of the field's 1694 * value type. 1695 * The method handle will take no arguments. 1696 * Access checking is performed immediately on behalf of the lookup class. 1697 * <p> 1698 * If the returned method handle is invoked, the field's class will 1699 * be initialized, if it has not already been initialized. 1700 * @param refc the class or interface from which the method is accessed 1701 * @param name the field's name 1702 * @param type the field's type 1703 * @return a method handle which can load values from the field 1704 * @throws NoSuchFieldException if the field does not exist 1705 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 1706 * @exception SecurityException if a security manager is present and it 1707 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1708 * @throws NullPointerException if any argument is null 1709 */ findStaticGetter(Class<?> refc, String name, Class<?> type)1710 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1711 return findAccessor(refc, name, type, MethodHandle.SGET); 1712 } 1713 1714 /** 1715 * Produces a method handle giving write access to a static field. 1716 * The type of the method handle will have a void return type. 1717 * The method handle will take a single 1718 * argument, of the field's value type, the value to be stored. 1719 * Access checking is performed immediately on behalf of the lookup class. 1720 * <p> 1721 * If the returned method handle is invoked, the field's class will 1722 * be initialized, if it has not already been initialized. 1723 * @param refc the class or interface from which the method is accessed 1724 * @param name the field's name 1725 * @param type the field's type 1726 * @return a method handle which can store values into the field 1727 * @throws NoSuchFieldException if the field does not exist 1728 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 1729 * @exception SecurityException if a security manager is present and it 1730 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1731 * @throws NullPointerException if any argument is null 1732 */ findStaticSetter(Class<?> refc, String name, Class<?> type)1733 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1734 return findAccessor(refc, name, type, MethodHandle.SPUT); 1735 } 1736 1737 // BEGIN Android-changed: OpenJDK 9+181 VarHandle API factory method. 1738 /** 1739 * Produces a VarHandle giving access to a static field {@code name} of 1740 * type {@code type} declared in a class of type {@code decl}. 1741 * The VarHandle's variable type is {@code type} and it has no 1742 * coordinate types. 1743 * <p> 1744 * Access checking is performed immediately on behalf of the lookup 1745 * class. 1746 * <p> 1747 * If the returned VarHandle is operated on, the declaring class will be 1748 * initialized, if it has not already been initialized. 1749 * <p> 1750 * Certain access modes of the returned VarHandle are unsupported under 1751 * the following conditions: 1752 * <ul> 1753 * <li>if the field is declared {@code final}, then the write, atomic 1754 * update, numeric atomic update, and bitwise atomic update access 1755 * modes are unsupported. 1756 * <li>if the field type is anything other than {@code byte}, 1757 * {@code short}, {@code char}, {@code int}, {@code long}, 1758 * {@code float}, or {@code double}, then numeric atomic update 1759 * access modes are unsupported. 1760 * <li>if the field type is anything other than {@code boolean}, 1761 * {@code byte}, {@code short}, {@code char}, {@code int} or 1762 * {@code long} then bitwise atomic update access modes are 1763 * unsupported. 1764 * </ul> 1765 * <p> 1766 * If the field is declared {@code volatile} then the returned VarHandle 1767 * will override access to the field (effectively ignore the 1768 * {@code volatile} declaration) in accordance to its specified 1769 * access modes. 1770 * <p> 1771 * If the field type is {@code float} or {@code double} then numeric 1772 * and atomic update access modes compare values using their bitwise 1773 * representation (see {@link Float#floatToRawIntBits} and 1774 * {@link Double#doubleToRawLongBits}, respectively). 1775 * @apiNote 1776 * Bitwise comparison of {@code float} values or {@code double} values, 1777 * as performed by the numeric and atomic update access modes, differ 1778 * from the primitive {@code ==} operator and the {@link Float#equals} 1779 * and {@link Double#equals} methods, specifically with respect to 1780 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 1781 * Care should be taken when performing a compare and set or a compare 1782 * and exchange operation with such values since the operation may 1783 * unexpectedly fail. 1784 * There are many possible NaN values that are considered to be 1785 * {@code NaN} in Java, although no IEEE 754 floating-point operation 1786 * provided by Java can distinguish between them. Operation failure can 1787 * occur if the expected or witness value is a NaN value and it is 1788 * transformed (perhaps in a platform specific manner) into another NaN 1789 * value, and thus has a different bitwise representation (see 1790 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 1791 * details). 1792 * The values {@code -0.0} and {@code +0.0} have different bitwise 1793 * representations but are considered equal when using the primitive 1794 * {@code ==} operator. Operation failure can occur if, for example, a 1795 * numeric algorithm computes an expected value to be say {@code -0.0} 1796 * and previously computed the witness value to be say {@code +0.0}. 1797 * @param decl the class that declares the static field 1798 * @param name the field's name 1799 * @param type the field's type, of type {@code T} 1800 * @return a VarHandle giving access to a static field 1801 * @throws NoSuchFieldException if the field does not exist 1802 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 1803 * @exception SecurityException if a security manager is present and it 1804 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1805 * @throws NullPointerException if any argument is null 1806 * @since 9 1807 */ findStaticVarHandle(Class<?> decl, String name, Class<?> type)1808 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1809 final Field field = findFieldOfType(decl, name, type); 1810 final boolean isStatic = true; 1811 final boolean performAccessChecks = true; 1812 commonFieldChecks(field, decl, type, isStatic, performAccessChecks); 1813 return StaticFieldVarHandle.create(field); 1814 } 1815 // END Android-changed: OpenJDK 9+181 VarHandle API factory method. 1816 1817 /** 1818 * Produces an early-bound method handle for a non-static method. 1819 * The receiver must have a supertype {@code defc} in which a method 1820 * of the given name and type is accessible to the lookup class. 1821 * The method and all its argument types must be accessible to the lookup object. 1822 * The type of the method handle will be that of the method, 1823 * without any insertion of an additional receiver parameter. 1824 * The given receiver will be bound into the method handle, 1825 * so that every call to the method handle will invoke the 1826 * requested method on the given receiver. 1827 * <p> 1828 * The returned method handle will have 1829 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1830 * the method's variable arity modifier bit ({@code 0x0080}) is set 1831 * <em>and</em> the trailing array argument is not the only argument. 1832 * (If the trailing array argument is the only argument, 1833 * the given receiver value will be bound to it.) 1834 * <p> 1835 * This is equivalent to the following code: 1836 * <blockquote><pre>{@code 1837 import static java.lang.invoke.MethodHandles.*; 1838 import static java.lang.invoke.MethodType.*; 1839 ... 1840 MethodHandle mh0 = lookup().findVirtual(defc, name, type); 1841 MethodHandle mh1 = mh0.bindTo(receiver); 1842 MethodType mt1 = mh1.type(); 1843 if (mh0.isVarargsCollector()) 1844 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1)); 1845 return mh1; 1846 * }</pre></blockquote> 1847 * where {@code defc} is either {@code receiver.getClass()} or a super 1848 * type of that class, in which the requested method is accessible 1849 * to the lookup class. 1850 * (Note that {@code bindTo} does not preserve variable arity.) 1851 * @param receiver the object from which the method is accessed 1852 * @param name the name of the method 1853 * @param type the type of the method, with the receiver argument omitted 1854 * @return the desired method handle 1855 * @throws NoSuchMethodException if the method does not exist 1856 * @throws IllegalAccessException if access checking fails 1857 * or if the method's variable arity modifier bit 1858 * is set and {@code asVarargsCollector} fails 1859 * @exception SecurityException if a security manager is present and it 1860 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1861 * @throws NullPointerException if any argument is null 1862 * @see MethodHandle#bindTo 1863 * @see #findVirtual 1864 */ bind(Object receiver, String name, MethodType type)1865 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 1866 MethodHandle handle = findVirtual(receiver.getClass(), name, type); 1867 MethodHandle adapter = handle.bindTo(receiver); 1868 MethodType adapterType = adapter.type(); 1869 if (handle.isVarargsCollector()) { 1870 adapter = adapter.asVarargsCollector( 1871 adapterType.parameterType(adapterType.parameterCount() - 1)); 1872 } 1873 1874 return adapter; 1875 } 1876 1877 /** 1878 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 1879 * to <i>m</i>, if the lookup class has permission. 1880 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument. 1881 * If <i>m</i> is virtual, overriding is respected on every call. 1882 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped. 1883 * The type of the method handle will be that of the method, 1884 * with the receiver type prepended (but only if it is non-static). 1885 * If the method's {@code accessible} flag is not set, 1886 * access checking is performed immediately on behalf of the lookup class. 1887 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties. 1888 * <p> 1889 * The returned method handle will have 1890 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1891 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1892 * <p> 1893 * If <i>m</i> is static, and 1894 * if the returned method handle is invoked, the method's class will 1895 * be initialized, if it has not already been initialized. 1896 * @param m the reflected method 1897 * @return a method handle which can invoke the reflected method 1898 * @throws IllegalAccessException if access checking fails 1899 * or if the method's variable arity modifier bit 1900 * is set and {@code asVarargsCollector} fails 1901 * @throws NullPointerException if the argument is null 1902 */ unreflect(Method m)1903 public MethodHandle unreflect(Method m) throws IllegalAccessException { 1904 if (m == null) { 1905 throw new NullPointerException("m == null"); 1906 } 1907 1908 MethodType methodType = MethodType.methodType(m.getReturnType(), 1909 m.getParameterTypes()); 1910 1911 // We should only perform access checks if setAccessible hasn't been called yet. 1912 if (!m.isAccessible()) { 1913 checkAccess(m.getDeclaringClass(), m.getDeclaringClass(), m.getModifiers(), 1914 m.getName()); 1915 } 1916 1917 if (Modifier.isStatic(m.getModifiers())) { 1918 return createMethodHandle(m, MethodHandle.INVOKE_STATIC, methodType); 1919 } else { 1920 methodType = methodType.insertParameterTypes(0, m.getDeclaringClass()); 1921 return createMethodHandle(m, MethodHandle.INVOKE_VIRTUAL, methodType); 1922 } 1923 } 1924 1925 /** 1926 * Produces a method handle for a reflected method. 1927 * It will bypass checks for overriding methods on the receiver, 1928 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 1929 * instruction from within the explicitly specified {@code specialCaller}. 1930 * The type of the method handle will be that of the method, 1931 * with a suitably restricted receiver type prepended. 1932 * (The receiver type will be {@code specialCaller} or a subtype.) 1933 * If the method's {@code accessible} flag is not set, 1934 * access checking is performed immediately on behalf of the lookup class, 1935 * as if {@code invokespecial} instruction were being linked. 1936 * <p> 1937 * Before method resolution, 1938 * if the explicitly specified caller class is not identical with the 1939 * lookup class, or if this lookup object does not have 1940 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 1941 * privileges, the access fails. 1942 * <p> 1943 * The returned method handle will have 1944 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1945 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1946 * @param m the reflected method 1947 * @param specialCaller the class nominally calling the method 1948 * @return a method handle which can invoke the reflected method 1949 * @throws IllegalAccessException if access checking fails 1950 * or if the method's variable arity modifier bit 1951 * is set and {@code asVarargsCollector} fails 1952 * @throws NullPointerException if any argument is null 1953 */ unreflectSpecial(Method m, Class<?> specialCaller)1954 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException { 1955 if (m == null) { 1956 throw new NullPointerException("m == null"); 1957 } 1958 1959 if (specialCaller == null) { 1960 throw new NullPointerException("specialCaller == null"); 1961 } 1962 1963 if (!m.isAccessible()) { 1964 // Android-changed: Match Java language 9 behavior where unreflectSpecial continues 1965 // to require exact caller lookupClass match. 1966 checkSpecialCaller(specialCaller, null); 1967 } 1968 1969 final MethodType methodType = MethodType.methodType(m.getReturnType(), 1970 m.getParameterTypes()); 1971 return findSpecial(m, methodType, m.getDeclaringClass() /* refc */, specialCaller); 1972 } 1973 1974 /** 1975 * Produces a method handle for a reflected constructor. 1976 * The type of the method handle will be that of the constructor, 1977 * with the return type changed to the declaring class. 1978 * The method handle will perform a {@code newInstance} operation, 1979 * creating a new instance of the constructor's class on the 1980 * arguments passed to the method handle. 1981 * <p> 1982 * If the constructor's {@code accessible} flag is not set, 1983 * access checking is performed immediately on behalf of the lookup class. 1984 * <p> 1985 * The returned method handle will have 1986 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1987 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 1988 * <p> 1989 * If the returned method handle is invoked, the constructor's class will 1990 * be initialized, if it has not already been initialized. 1991 * @param c the reflected constructor 1992 * @return a method handle which can invoke the reflected constructor 1993 * @throws IllegalAccessException if access checking fails 1994 * or if the method's variable arity modifier bit 1995 * is set and {@code asVarargsCollector} fails 1996 * @throws NullPointerException if the argument is null 1997 */ unreflectConstructor(Constructor<?> c)1998 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException { 1999 if (c == null) { 2000 throw new NullPointerException("c == null"); 2001 } 2002 2003 if (!c.isAccessible()) { 2004 checkAccess(c.getDeclaringClass(), c.getDeclaringClass(), c.getModifiers(), 2005 c.getName()); 2006 } 2007 2008 return createMethodHandleForConstructor(c); 2009 } 2010 2011 /** 2012 * Produces a method handle giving read access to a reflected field. 2013 * The type of the method handle will have a return type of the field's 2014 * value type. 2015 * If the field is static, the method handle will take no arguments. 2016 * Otherwise, its single argument will be the instance containing 2017 * the field. 2018 * If the field's {@code accessible} flag is not set, 2019 * access checking is performed immediately on behalf of the lookup class. 2020 * <p> 2021 * If the field is static, and 2022 * if the returned method handle is invoked, the field's class will 2023 * be initialized, if it has not already been initialized. 2024 * @param f the reflected field 2025 * @return a method handle which can load values from the reflected field 2026 * @throws IllegalAccessException if access checking fails 2027 * @throws NullPointerException if the argument is null 2028 */ unreflectGetter(Field f)2029 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException { 2030 return findAccessor(f, f.getDeclaringClass(), f.getType(), 2031 Modifier.isStatic(f.getModifiers()) ? MethodHandle.SGET : MethodHandle.IGET, 2032 !f.isAccessible() /* performAccessChecks */); 2033 } 2034 2035 /** 2036 * Produces a method handle giving write access to a reflected field. 2037 * The type of the method handle will have a void return type. 2038 * If the field is static, the method handle will take a single 2039 * argument, of the field's value type, the value to be stored. 2040 * Otherwise, the two arguments will be the instance containing 2041 * the field, and the value to be stored. 2042 * If the field's {@code accessible} flag is not set, 2043 * access checking is performed immediately on behalf of the lookup class. 2044 * <p> 2045 * If the field is static, and 2046 * if the returned method handle is invoked, the field's class will 2047 * be initialized, if it has not already been initialized. 2048 * @param f the reflected field 2049 * @return a method handle which can store values into the reflected field 2050 * @throws IllegalAccessException if access checking fails 2051 * @throws NullPointerException if the argument is null 2052 */ unreflectSetter(Field f)2053 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException { 2054 return findAccessor(f, f.getDeclaringClass(), f.getType(), 2055 Modifier.isStatic(f.getModifiers()) ? MethodHandle.SPUT : MethodHandle.IPUT, 2056 !f.isAccessible() /* performAccessChecks */); 2057 } 2058 2059 // BEGIN Android-changed: OpenJDK 9+181 VarHandle API factory method. 2060 /** 2061 * Produces a VarHandle giving access to a reflected field {@code f} 2062 * of type {@code T} declared in a class of type {@code R}. 2063 * The VarHandle's variable type is {@code T}. 2064 * If the field is non-static the VarHandle has one coordinate type, 2065 * {@code R}. Otherwise, the field is static, and the VarHandle has no 2066 * coordinate types. 2067 * <p> 2068 * Access checking is performed immediately on behalf of the lookup 2069 * class, regardless of the value of the field's {@code accessible} 2070 * flag. 2071 * <p> 2072 * If the field is static, and if the returned VarHandle is operated 2073 * on, the field's declaring class will be initialized, if it has not 2074 * already been initialized. 2075 * <p> 2076 * Certain access modes of the returned VarHandle are unsupported under 2077 * the following conditions: 2078 * <ul> 2079 * <li>if the field is declared {@code final}, then the write, atomic 2080 * update, numeric atomic update, and bitwise atomic update access 2081 * modes are unsupported. 2082 * <li>if the field type is anything other than {@code byte}, 2083 * {@code short}, {@code char}, {@code int}, {@code long}, 2084 * {@code float}, or {@code double} then numeric atomic update 2085 * access modes are unsupported. 2086 * <li>if the field type is anything other than {@code boolean}, 2087 * {@code byte}, {@code short}, {@code char}, {@code int} or 2088 * {@code long} then bitwise atomic update access modes are 2089 * unsupported. 2090 * </ul> 2091 * <p> 2092 * If the field is declared {@code volatile} then the returned VarHandle 2093 * will override access to the field (effectively ignore the 2094 * {@code volatile} declaration) in accordance to its specified 2095 * access modes. 2096 * <p> 2097 * If the field type is {@code float} or {@code double} then numeric 2098 * and atomic update access modes compare values using their bitwise 2099 * representation (see {@link Float#floatToRawIntBits} and 2100 * {@link Double#doubleToRawLongBits}, respectively). 2101 * @apiNote 2102 * Bitwise comparison of {@code float} values or {@code double} values, 2103 * as performed by the numeric and atomic update access modes, differ 2104 * from the primitive {@code ==} operator and the {@link Float#equals} 2105 * and {@link Double#equals} methods, specifically with respect to 2106 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 2107 * Care should be taken when performing a compare and set or a compare 2108 * and exchange operation with such values since the operation may 2109 * unexpectedly fail. 2110 * There are many possible NaN values that are considered to be 2111 * {@code NaN} in Java, although no IEEE 754 floating-point operation 2112 * provided by Java can distinguish between them. Operation failure can 2113 * occur if the expected or witness value is a NaN value and it is 2114 * transformed (perhaps in a platform specific manner) into another NaN 2115 * value, and thus has a different bitwise representation (see 2116 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 2117 * details). 2118 * The values {@code -0.0} and {@code +0.0} have different bitwise 2119 * representations but are considered equal when using the primitive 2120 * {@code ==} operator. Operation failure can occur if, for example, a 2121 * numeric algorithm computes an expected value to be say {@code -0.0} 2122 * and previously computed the witness value to be say {@code +0.0}. 2123 * @param f the reflected field, with a field of type {@code T}, and 2124 * a declaring class of type {@code R} 2125 * @return a VarHandle giving access to non-static fields or a static 2126 * field 2127 * @throws IllegalAccessException if access checking fails 2128 * @throws NullPointerException if the argument is null 2129 * @since 9 2130 */ unreflectVarHandle(Field f)2131 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException { 2132 final boolean isStatic = Modifier.isStatic(f.getModifiers()); 2133 final boolean performAccessChecks = true; 2134 commonFieldChecks(f, f.getDeclaringClass(), f.getType(), isStatic, performAccessChecks); 2135 return isStatic ? StaticFieldVarHandle.create(f) : FieldVarHandle.create(f); 2136 } 2137 // END Android-changed: OpenJDK 9+181 VarHandle API factory method. 2138 2139 /** 2140 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 2141 * created by this lookup object or a similar one. 2142 * Security and access checks are performed to ensure that this lookup object 2143 * is capable of reproducing the target method handle. 2144 * This means that the cracking may fail if target is a direct method handle 2145 * but was created by an unrelated lookup object. 2146 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> 2147 * and was created by a lookup object for a different class. 2148 * @param target a direct method handle to crack into symbolic reference components 2149 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object 2150 * @exception SecurityException if a security manager is present and it 2151 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2152 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails 2153 * @exception NullPointerException if the target is {@code null} 2154 * @see MethodHandleInfo 2155 * @since 1.8 2156 */ revealDirect(MethodHandle target)2157 public MethodHandleInfo revealDirect(MethodHandle target) { 2158 MethodHandleImpl directTarget = getMethodHandleImpl(target); 2159 MethodHandleInfo info = directTarget.reveal(); 2160 2161 try { 2162 checkAccess(lookupClass(), info.getDeclaringClass(), info.getModifiers(), 2163 info.getName()); 2164 } catch (IllegalAccessException exception) { 2165 throw new IllegalArgumentException("Unable to access memeber.", exception); 2166 } 2167 2168 return info; 2169 } 2170 hasPrivateAccess()2171 private boolean hasPrivateAccess() { 2172 return (allowedModes & PRIVATE) != 0; 2173 } 2174 2175 /** Check public/protected/private bits on the symbolic reference class and its member. */ checkAccess(Class<?> refc, Class<?> defc, int mods, String methName)2176 void checkAccess(Class<?> refc, Class<?> defc, int mods, String methName) 2177 throws IllegalAccessException { 2178 int allowedModes = this.allowedModes; 2179 2180 if (Modifier.isProtected(mods) && 2181 defc == Object.class && 2182 "clone".equals(methName) && 2183 refc.isArray()) { 2184 // The JVM does this hack also. 2185 // (See ClassVerifier::verify_invoke_instructions 2186 // and LinkResolver::check_method_accessability.) 2187 // Because the JVM does not allow separate methods on array types, 2188 // there is no separate method for int[].clone. 2189 // All arrays simply inherit Object.clone. 2190 // But for access checking logic, we make Object.clone 2191 // (normally protected) appear to be public. 2192 // Later on, when the DirectMethodHandle is created, 2193 // its leading argument will be restricted to the 2194 // requested array type. 2195 // N.B. The return type is not adjusted, because 2196 // that is *not* the bytecode behavior. 2197 mods ^= Modifier.PROTECTED | Modifier.PUBLIC; 2198 } 2199 2200 if (Modifier.isProtected(mods) && Modifier.isConstructor(mods)) { 2201 // cannot "new" a protected ctor in a different package 2202 mods ^= Modifier.PROTECTED; 2203 } 2204 2205 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0) 2206 return; // common case 2207 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE 2208 if ((requestedModes & allowedModes) != 0) { 2209 if (VerifyAccess.isMemberAccessible(refc, defc, mods, lookupClass(), allowedModes)) 2210 return; 2211 } else { 2212 // Protected members can also be checked as if they were package-private. 2213 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0 2214 && VerifyAccess.isSamePackage(defc, lookupClass())) 2215 return; 2216 } 2217 2218 throwMakeAccessException(accessFailedMessage(refc, defc, mods), this); 2219 } 2220 accessFailedMessage(Class<?> refc, Class<?> defc, int mods)2221 String accessFailedMessage(Class<?> refc, Class<?> defc, int mods) { 2222 // check the class first: 2223 boolean classOK = (Modifier.isPublic(defc.getModifiers()) && 2224 (defc == refc || 2225 Modifier.isPublic(refc.getModifiers()))); 2226 if (!classOK && (allowedModes & PACKAGE) != 0) { 2227 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) && 2228 (defc == refc || 2229 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES))); 2230 } 2231 if (!classOK) 2232 return "class is not public"; 2233 if (Modifier.isPublic(mods)) 2234 return "access to public member failed"; // (how?) 2235 if (Modifier.isPrivate(mods)) 2236 return "member is private"; 2237 if (Modifier.isProtected(mods)) 2238 return "member is protected"; 2239 return "member is private to package"; 2240 } 2241 2242 // Android-changed: checkSpecialCaller assumes that ALLOW_NESTMATE_ACCESS = false, 2243 // as in upstream OpenJDK. 2244 // 2245 // private static final boolean ALLOW_NESTMATE_ACCESS = false; 2246 2247 // Android-changed: Match java language 9 behavior allowing special access if the reflected 2248 // class (called 'refc', the class from which the method is being accessed) is an interface 2249 // and is implemented by the caller. checkSpecialCaller(Class<?> specialCaller, Class<?> refc)2250 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException { 2251 // Android-changed: No support for TRUSTED lookups. Also construct the 2252 // IllegalAccessException by hand because the upstream code implicitly assumes 2253 // that the lookupClass == specialCaller. 2254 // 2255 // if (allowedModes == TRUSTED) return; 2256 boolean isInterfaceLookup = (refc != null && 2257 refc.isInterface() && 2258 refc.isAssignableFrom(specialCaller)); 2259 if (!hasPrivateAccess() || (specialCaller != lookupClass() && !isInterfaceLookup)) { 2260 throw new IllegalAccessException("no private access for invokespecial : " 2261 + specialCaller + ", from" + this); 2262 } 2263 } 2264 throwMakeAccessException(String message, Object from)2265 private void throwMakeAccessException(String message, Object from) throws 2266 IllegalAccessException{ 2267 message = message + ": "+ toString(); 2268 if (from != null) message += ", from " + from; 2269 throw new IllegalAccessException(message); 2270 } 2271 checkReturnType(Method method, MethodType methodType)2272 private void checkReturnType(Method method, MethodType methodType) 2273 throws NoSuchMethodException { 2274 if (method.getReturnType() != methodType.rtype()) { 2275 throw new NoSuchMethodException(method.getName() + methodType); 2276 } 2277 } 2278 } 2279 2280 /** 2281 * "Cracks" {@code target} to reveal the underlying {@code MethodHandleImpl}. 2282 */ getMethodHandleImpl(MethodHandle target)2283 private static MethodHandleImpl getMethodHandleImpl(MethodHandle target) { 2284 // Special case : We implement handles to constructors as transformers, 2285 // so we must extract the underlying handle from the transformer. 2286 if (target instanceof Transformers.Construct) { 2287 target = ((Transformers.Construct) target).getConstructorHandle(); 2288 } 2289 2290 // Special case: Var-args methods are also implemented as Transformers, 2291 // so we should get the underlying handle in that case as well. 2292 if (target instanceof Transformers.VarargsCollector) { 2293 target = target.asFixedArity(); 2294 } 2295 2296 if (target instanceof MethodHandleImpl) { 2297 return (MethodHandleImpl) target; 2298 } 2299 2300 throw new IllegalArgumentException(target + " is not a direct handle"); 2301 } 2302 2303 // Android-removed: unsupported @jvms tag in doc-comment. 2304 /** 2305 * Produces a method handle constructing arrays of a desired type, 2306 * as if by the {@code anewarray} bytecode. 2307 * The return type of the method handle will be the array type. 2308 * The type of its sole argument will be {@code int}, which specifies the size of the array. 2309 * 2310 * <p> If the returned method handle is invoked with a negative 2311 * array size, a {@code NegativeArraySizeException} will be thrown. 2312 * 2313 * @param arrayClass an array type 2314 * @return a method handle which can create arrays of the given type 2315 * @throws NullPointerException if the argument is {@code null} 2316 * @throws IllegalArgumentException if {@code arrayClass} is not an array type 2317 * @see java.lang.reflect.Array#newInstance(Class, int) 2318 * @since 9 2319 */ 2320 public static arrayConstructor(Class<?> arrayClass)2321 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException { 2322 if (!arrayClass.isArray()) { 2323 throw newIllegalArgumentException("not an array class: " + arrayClass.getName()); 2324 } 2325 // Android-changed: transformer based implementation. 2326 // MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance). 2327 // bindTo(arrayClass.getComponentType()); 2328 // return ani.asType(ani.type().changeReturnType(arrayClass)) 2329 return new Transformers.ArrayConstructor(arrayClass); 2330 } 2331 2332 // Android-removed: unsupported @jvms tag in doc-comment. 2333 /** 2334 * Produces a method handle returning the length of an array, 2335 * as if by the {@code arraylength} bytecode. 2336 * The type of the method handle will have {@code int} as return type, 2337 * and its sole argument will be the array type. 2338 * 2339 * <p> If the returned method handle is invoked with a {@code null} 2340 * array reference, a {@code NullPointerException} will be thrown. 2341 * 2342 * @param arrayClass an array type 2343 * @return a method handle which can retrieve the length of an array of the given array type 2344 * @throws NullPointerException if the argument is {@code null} 2345 * @throws IllegalArgumentException if arrayClass is not an array type 2346 * @since 9 2347 */ 2348 public static arrayLength(Class<?> arrayClass)2349 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException { 2350 // Android-changed: calling static function directly. 2351 // return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH); 2352 if (!arrayClass.isArray()) { 2353 throw newIllegalArgumentException("not an array class: " + arrayClass.getName()); 2354 } 2355 Class<?> componentType = arrayClass.getComponentType(); 2356 Class<?> reducedArrayType = componentType.isPrimitive() ? arrayClass : Object[].class; 2357 2358 try { 2359 Method arrayLength = 2360 MethodHandles.class.getDeclaredMethod("arrayLength", reducedArrayType); 2361 2362 return new MethodHandleImpl( 2363 arrayLength.getArtMethod(), 2364 MethodHandle.INVOKE_STATIC, 2365 MethodType.methodType(int.class, arrayClass)); 2366 } catch (NoSuchMethodException nsme) { 2367 throw new AssertionError(nsme); 2368 } 2369 } 2370 2371 // BEGIN Android-added: method to check if a class is an array. checkClassIsArray(Class<?> c)2372 private static void checkClassIsArray(Class<?> c) { 2373 if (!c.isArray()) { 2374 throw new IllegalArgumentException("Not an array type: " + c); 2375 } 2376 } 2377 arrayLength(byte[] array)2378 private static int arrayLength(byte[] array) { return array.length; } arrayLength(boolean[] array)2379 private static int arrayLength(boolean[] array) { return array.length; } arrayLength(char[] array)2380 private static int arrayLength(char[] array) { return array.length; } arrayLength(short[] array)2381 private static int arrayLength(short[] array) { return array.length; } arrayLength(int[] array)2382 private static int arrayLength(int[] array) { return array.length; } arrayLength(long[] array)2383 private static int arrayLength(long[] array) { return array.length; } arrayLength(float[] array)2384 private static int arrayLength(float[] array) { return array.length; } arrayLength(double[] array)2385 private static int arrayLength(double[] array) { return array.length; } arrayLength(Object[] array)2386 private static int arrayLength(Object[] array) { return array.length; } 2387 checkTypeIsViewable(Class<?> componentType)2388 private static void checkTypeIsViewable(Class<?> componentType) { 2389 if (componentType == short.class || 2390 componentType == char.class || 2391 componentType == int.class || 2392 componentType == long.class || 2393 componentType == float.class || 2394 componentType == double.class) { 2395 return; 2396 } 2397 throw new UnsupportedOperationException("Component type not supported: " + componentType); 2398 } 2399 // END Android-added: method to check if a class is an array. 2400 2401 /** 2402 * Produces a method handle giving read access to elements of an array. 2403 * The type of the method handle will have a return type of the array's 2404 * element type. Its first argument will be the array type, 2405 * and the second will be {@code int}. 2406 * @param arrayClass an array type 2407 * @return a method handle which can load values from the given array type 2408 * @throws NullPointerException if the argument is null 2409 * @throws IllegalArgumentException if arrayClass is not an array type 2410 */ 2411 public static arrayElementGetter(Class<?> arrayClass)2412 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException { 2413 checkClassIsArray(arrayClass); 2414 final Class<?> componentType = arrayClass.getComponentType(); 2415 if (componentType.isPrimitive()) { 2416 try { 2417 return Lookup.PUBLIC_LOOKUP.findStatic(MethodHandles.class, 2418 "arrayElementGetter", 2419 MethodType.methodType(componentType, arrayClass, int.class)); 2420 } catch (NoSuchMethodException | IllegalAccessException exception) { 2421 throw new AssertionError(exception); 2422 } 2423 } 2424 2425 try { 2426 // MethodHandle objects can be cached. 2427 Method arrayElementGetter = 2428 MethodHandles.class.getDeclaredMethod( 2429 "arrayElementGetter", Object[].class, int.class); 2430 2431 return new MethodHandleImpl( 2432 arrayElementGetter.getArtMethod(), 2433 MethodHandle.INVOKE_STATIC, 2434 MethodType.methodType(componentType, arrayClass, int.class)); 2435 } catch (NoSuchMethodException nsme) { 2436 throw new AssertionError(nsme); 2437 } 2438 } 2439 arrayElementGetter(byte[] array, int i)2440 /** @hide */ public static byte arrayElementGetter(byte[] array, int i) { return array[i]; } arrayElementGetter(boolean[] array, int i)2441 /** @hide */ public static boolean arrayElementGetter(boolean[] array, int i) { return array[i]; } arrayElementGetter(char[] array, int i)2442 /** @hide */ public static char arrayElementGetter(char[] array, int i) { return array[i]; } arrayElementGetter(short[] array, int i)2443 /** @hide */ public static short arrayElementGetter(short[] array, int i) { return array[i]; } arrayElementGetter(int[] array, int i)2444 /** @hide */ public static int arrayElementGetter(int[] array, int i) { return array[i]; } arrayElementGetter(long[] array, int i)2445 /** @hide */ public static long arrayElementGetter(long[] array, int i) { return array[i]; } arrayElementGetter(float[] array, int i)2446 /** @hide */ public static float arrayElementGetter(float[] array, int i) { return array[i]; } arrayElementGetter(double[] array, int i)2447 /** @hide */ public static double arrayElementGetter(double[] array, int i) { return array[i]; } arrayElementGetter(Object[] array, int i)2448 private static Object arrayElementGetter(Object[] array, int i) { return array[i]; } 2449 2450 /** 2451 * Produces a method handle giving write access to elements of an array. 2452 * The type of the method handle will have a void return type. 2453 * Its last argument will be the array's element type. 2454 * The first and second arguments will be the array type and int. 2455 * @param arrayClass the class of an array 2456 * @return a method handle which can store values into the array type 2457 * @throws NullPointerException if the argument is null 2458 * @throws IllegalArgumentException if arrayClass is not an array type 2459 */ 2460 public static arrayElementSetter(Class<?> arrayClass)2461 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException { 2462 checkClassIsArray(arrayClass); 2463 final Class<?> componentType = arrayClass.getComponentType(); 2464 if (componentType.isPrimitive()) { 2465 try { 2466 return Lookup.PUBLIC_LOOKUP.findStatic(MethodHandles.class, 2467 "arrayElementSetter", 2468 MethodType.methodType(void.class, arrayClass, int.class, componentType)); 2469 } catch (NoSuchMethodException | IllegalAccessException exception) { 2470 throw new AssertionError(exception); 2471 } 2472 } 2473 2474 try { 2475 Method arrayElementSetter = 2476 MethodHandles.class.getDeclaredMethod( 2477 "arrayElementSetter", Object[].class, int.class, Object.class); 2478 2479 return new MethodHandleImpl( 2480 arrayElementSetter.getArtMethod(), 2481 MethodHandle.INVOKE_STATIC, 2482 MethodType.methodType(void.class, arrayClass, int.class, componentType)); 2483 } catch (NoSuchMethodException nsme) { 2484 throw new AssertionError(nsme); 2485 } 2486 } 2487 2488 /** @hide */ arrayElementSetter(byte[] array, int i, byte val)2489 public static void arrayElementSetter(byte[] array, int i, byte val) { array[i] = val; } 2490 /** @hide */ arrayElementSetter(boolean[] array, int i, boolean val)2491 public static void arrayElementSetter(boolean[] array, int i, boolean val) { array[i] = val; } 2492 /** @hide */ arrayElementSetter(char[] array, int i, char val)2493 public static void arrayElementSetter(char[] array, int i, char val) { array[i] = val; } 2494 /** @hide */ arrayElementSetter(short[] array, int i, short val)2495 public static void arrayElementSetter(short[] array, int i, short val) { array[i] = val; } 2496 /** @hide */ arrayElementSetter(int[] array, int i, int val)2497 public static void arrayElementSetter(int[] array, int i, int val) { array[i] = val; } 2498 /** @hide */ arrayElementSetter(long[] array, int i, long val)2499 public static void arrayElementSetter(long[] array, int i, long val) { array[i] = val; } 2500 /** @hide */ arrayElementSetter(float[] array, int i, float val)2501 public static void arrayElementSetter(float[] array, int i, float val) { array[i] = val; } 2502 /** @hide */ arrayElementSetter(double[] array, int i, double val)2503 public static void arrayElementSetter(double[] array, int i, double val) { array[i] = val; } arrayElementSetter(Object[] array, int i, Object val)2504 private static void arrayElementSetter(Object[] array, int i, Object val) { array[i] = val; } 2505 2506 // BEGIN Android-changed: OpenJDK 9+181 VarHandle API factory methods. 2507 /** 2508 * Produces a VarHandle giving access to elements of an array of type 2509 * {@code arrayClass}. The VarHandle's variable type is the component type 2510 * of {@code arrayClass} and the list of coordinate types is 2511 * {@code (arrayClass, int)}, where the {@code int} coordinate type 2512 * corresponds to an argument that is an index into an array. 2513 * <p> 2514 * Certain access modes of the returned VarHandle are unsupported under 2515 * the following conditions: 2516 * <ul> 2517 * <li>if the component type is anything other than {@code byte}, 2518 * {@code short}, {@code char}, {@code int}, {@code long}, 2519 * {@code float}, or {@code double} then numeric atomic update access 2520 * modes are unsupported. 2521 * <li>if the field type is anything other than {@code boolean}, 2522 * {@code byte}, {@code short}, {@code char}, {@code int} or 2523 * {@code long} then bitwise atomic update access modes are 2524 * unsupported. 2525 * </ul> 2526 * <p> 2527 * If the component type is {@code float} or {@code double} then numeric 2528 * and atomic update access modes compare values using their bitwise 2529 * representation (see {@link Float#floatToRawIntBits} and 2530 * {@link Double#doubleToRawLongBits}, respectively). 2531 * @apiNote 2532 * Bitwise comparison of {@code float} values or {@code double} values, 2533 * as performed by the numeric and atomic update access modes, differ 2534 * from the primitive {@code ==} operator and the {@link Float#equals} 2535 * and {@link Double#equals} methods, specifically with respect to 2536 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 2537 * Care should be taken when performing a compare and set or a compare 2538 * and exchange operation with such values since the operation may 2539 * unexpectedly fail. 2540 * There are many possible NaN values that are considered to be 2541 * {@code NaN} in Java, although no IEEE 754 floating-point operation 2542 * provided by Java can distinguish between them. Operation failure can 2543 * occur if the expected or witness value is a NaN value and it is 2544 * transformed (perhaps in a platform specific manner) into another NaN 2545 * value, and thus has a different bitwise representation (see 2546 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 2547 * details). 2548 * The values {@code -0.0} and {@code +0.0} have different bitwise 2549 * representations but are considered equal when using the primitive 2550 * {@code ==} operator. Operation failure can occur if, for example, a 2551 * numeric algorithm computes an expected value to be say {@code -0.0} 2552 * and previously computed the witness value to be say {@code +0.0}. 2553 * @param arrayClass the class of an array, of type {@code T[]} 2554 * @return a VarHandle giving access to elements of an array 2555 * @throws NullPointerException if the arrayClass is null 2556 * @throws IllegalArgumentException if arrayClass is not an array type 2557 * @since 9 2558 */ 2559 public static arrayElementVarHandle(Class<?> arrayClass)2560 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException { 2561 checkClassIsArray(arrayClass); 2562 return ArrayElementVarHandle.create(arrayClass); 2563 } 2564 2565 /** 2566 * Produces a VarHandle giving access to elements of a {@code byte[]} array 2567 * viewed as if it were a different primitive array type, such as 2568 * {@code int[]} or {@code long[]}. 2569 * The VarHandle's variable type is the component type of 2570 * {@code viewArrayClass} and the list of coordinate types is 2571 * {@code (byte[], int)}, where the {@code int} coordinate type 2572 * corresponds to an argument that is an index into a {@code byte[]} array. 2573 * The returned VarHandle accesses bytes at an index in a {@code byte[]} 2574 * array, composing bytes to or from a value of the component type of 2575 * {@code viewArrayClass} according to the given endianness. 2576 * <p> 2577 * The supported component types (variables types) are {@code short}, 2578 * {@code char}, {@code int}, {@code long}, {@code float} and 2579 * {@code double}. 2580 * <p> 2581 * Access of bytes at a given index will result in an 2582 * {@code IndexOutOfBoundsException} if the index is less than {@code 0} 2583 * or greater than the {@code byte[]} array length minus the size (in bytes) 2584 * of {@code T}. 2585 * <p> 2586 * Access of bytes at an index may be aligned or misaligned for {@code T}, 2587 * with respect to the underlying memory address, {@code A} say, associated 2588 * with the array and index. 2589 * If access is misaligned then access for anything other than the 2590 * {@code get} and {@code set} access modes will result in an 2591 * {@code IllegalStateException}. In such cases atomic access is only 2592 * guaranteed with respect to the largest power of two that divides the GCD 2593 * of {@code A} and the size (in bytes) of {@code T}. 2594 * If access is aligned then following access modes are supported and are 2595 * guaranteed to support atomic access: 2596 * <ul> 2597 * <li>read write access modes for all {@code T}, with the exception of 2598 * access modes {@code get} and {@code set} for {@code long} and 2599 * {@code double} on 32-bit platforms. 2600 * <li>atomic update access modes for {@code int}, {@code long}, 2601 * {@code float} or {@code double}. 2602 * (Future major platform releases of the JDK may support additional 2603 * types for certain currently unsupported access modes.) 2604 * <li>numeric atomic update access modes for {@code int} and {@code long}. 2605 * (Future major platform releases of the JDK may support additional 2606 * numeric types for certain currently unsupported access modes.) 2607 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 2608 * (Future major platform releases of the JDK may support additional 2609 * numeric types for certain currently unsupported access modes.) 2610 * </ul> 2611 * <p> 2612 * Misaligned access, and therefore atomicity guarantees, may be determined 2613 * for {@code byte[]} arrays without operating on a specific array. Given 2614 * an {@code index}, {@code T} and it's corresponding boxed type, 2615 * {@code T_BOX}, misalignment may be determined as follows: 2616 * <pre>{@code 2617 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 2618 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]). 2619 * alignmentOffset(0, sizeOfT); 2620 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT; 2621 * boolean isMisaligned = misalignedAtIndex != 0; 2622 * }</pre> 2623 * <p> 2624 * If the variable type is {@code float} or {@code double} then atomic 2625 * update access modes compare values using their bitwise representation 2626 * (see {@link Float#floatToRawIntBits} and 2627 * {@link Double#doubleToRawLongBits}, respectively). 2628 * @param viewArrayClass the view array class, with a component type of 2629 * type {@code T} 2630 * @param byteOrder the endianness of the view array elements, as 2631 * stored in the underlying {@code byte} array 2632 * @return a VarHandle giving access to elements of a {@code byte[]} array 2633 * viewed as if elements corresponding to the components type of the view 2634 * array class 2635 * @throws NullPointerException if viewArrayClass or byteOrder is null 2636 * @throws IllegalArgumentException if viewArrayClass is not an array type 2637 * @throws UnsupportedOperationException if the component type of 2638 * viewArrayClass is not supported as a variable type 2639 * @since 9 2640 */ 2641 public static byteArrayViewVarHandle(Class<?> viewArrayClass, ByteOrder byteOrder)2642 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass, 2643 ByteOrder byteOrder) throws IllegalArgumentException { 2644 checkClassIsArray(viewArrayClass); 2645 checkTypeIsViewable(viewArrayClass.getComponentType()); 2646 return ByteArrayViewVarHandle.create(viewArrayClass, byteOrder); 2647 } 2648 2649 /** 2650 * Produces a VarHandle giving access to elements of a {@code ByteBuffer} 2651 * viewed as if it were an array of elements of a different primitive 2652 * component type to that of {@code byte}, such as {@code int[]} or 2653 * {@code long[]}. 2654 * The VarHandle's variable type is the component type of 2655 * {@code viewArrayClass} and the list of coordinate types is 2656 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type 2657 * corresponds to an argument that is an index into a {@code byte[]} array. 2658 * The returned VarHandle accesses bytes at an index in a 2659 * {@code ByteBuffer}, composing bytes to or from a value of the component 2660 * type of {@code viewArrayClass} according to the given endianness. 2661 * <p> 2662 * The supported component types (variables types) are {@code short}, 2663 * {@code char}, {@code int}, {@code long}, {@code float} and 2664 * {@code double}. 2665 * <p> 2666 * Access will result in a {@code ReadOnlyBufferException} for anything 2667 * other than the read access modes if the {@code ByteBuffer} is read-only. 2668 * <p> 2669 * Access of bytes at a given index will result in an 2670 * {@code IndexOutOfBoundsException} if the index is less than {@code 0} 2671 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of 2672 * {@code T}. 2673 * <p> 2674 * Access of bytes at an index may be aligned or misaligned for {@code T}, 2675 * with respect to the underlying memory address, {@code A} say, associated 2676 * with the {@code ByteBuffer} and index. 2677 * If access is misaligned then access for anything other than the 2678 * {@code get} and {@code set} access modes will result in an 2679 * {@code IllegalStateException}. In such cases atomic access is only 2680 * guaranteed with respect to the largest power of two that divides the GCD 2681 * of {@code A} and the size (in bytes) of {@code T}. 2682 * If access is aligned then following access modes are supported and are 2683 * guaranteed to support atomic access: 2684 * <ul> 2685 * <li>read write access modes for all {@code T}, with the exception of 2686 * access modes {@code get} and {@code set} for {@code long} and 2687 * {@code double} on 32-bit platforms. 2688 * <li>atomic update access modes for {@code int}, {@code long}, 2689 * {@code float} or {@code double}. 2690 * (Future major platform releases of the JDK may support additional 2691 * types for certain currently unsupported access modes.) 2692 * <li>numeric atomic update access modes for {@code int} and {@code long}. 2693 * (Future major platform releases of the JDK may support additional 2694 * numeric types for certain currently unsupported access modes.) 2695 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 2696 * (Future major platform releases of the JDK may support additional 2697 * numeric types for certain currently unsupported access modes.) 2698 * </ul> 2699 * <p> 2700 * Misaligned access, and therefore atomicity guarantees, may be determined 2701 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an 2702 * {@code index}, {@code T} and it's corresponding boxed type, 2703 * {@code T_BOX}, as follows: 2704 * <pre>{@code 2705 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 2706 * ByteBuffer bb = ... 2707 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT); 2708 * boolean isMisaligned = misalignedAtIndex != 0; 2709 * }</pre> 2710 * <p> 2711 * If the variable type is {@code float} or {@code double} then atomic 2712 * update access modes compare values using their bitwise representation 2713 * (see {@link Float#floatToRawIntBits} and 2714 * {@link Double#doubleToRawLongBits}, respectively). 2715 * @param viewArrayClass the view array class, with a component type of 2716 * type {@code T} 2717 * @param byteOrder the endianness of the view array elements, as 2718 * stored in the underlying {@code ByteBuffer} (Note this overrides the 2719 * endianness of a {@code ByteBuffer}) 2720 * @return a VarHandle giving access to elements of a {@code ByteBuffer} 2721 * viewed as if elements corresponding to the components type of the view 2722 * array class 2723 * @throws NullPointerException if viewArrayClass or byteOrder is null 2724 * @throws IllegalArgumentException if viewArrayClass is not an array type 2725 * @throws UnsupportedOperationException if the component type of 2726 * viewArrayClass is not supported as a variable type 2727 * @since 9 2728 */ 2729 public static byteBufferViewVarHandle(Class<?> viewArrayClass, ByteOrder byteOrder)2730 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass, 2731 ByteOrder byteOrder) throws IllegalArgumentException { 2732 checkClassIsArray(viewArrayClass); 2733 checkTypeIsViewable(viewArrayClass.getComponentType()); 2734 return ByteBufferViewVarHandle.create(viewArrayClass, byteOrder); 2735 } 2736 // END Android-changed: OpenJDK 9+181 VarHandle API factory methods. 2737 2738 /// method handle invocation (reflective style) 2739 2740 /** 2741 * Produces a method handle which will invoke any method handle of the 2742 * given {@code type}, with a given number of trailing arguments replaced by 2743 * a single trailing {@code Object[]} array. 2744 * The resulting invoker will be a method handle with the following 2745 * arguments: 2746 * <ul> 2747 * <li>a single {@code MethodHandle} target 2748 * <li>zero or more leading values (counted by {@code leadingArgCount}) 2749 * <li>an {@code Object[]} array containing trailing arguments 2750 * </ul> 2751 * <p> 2752 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with 2753 * the indicated {@code type}. 2754 * That is, if the target is exactly of the given {@code type}, it will behave 2755 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType} 2756 * is used to convert the target to the required {@code type}. 2757 * <p> 2758 * The type of the returned invoker will not be the given {@code type}, but rather 2759 * will have all parameters except the first {@code leadingArgCount} 2760 * replaced by a single array of type {@code Object[]}, which will be 2761 * the final parameter. 2762 * <p> 2763 * Before invoking its target, the invoker will spread the final array, apply 2764 * reference casts as necessary, and unbox and widen primitive arguments. 2765 * If, when the invoker is called, the supplied array argument does 2766 * not have the correct number of elements, the invoker will throw 2767 * an {@link IllegalArgumentException} instead of invoking the target. 2768 * <p> 2769 * This method is equivalent to the following code (though it may be more efficient): 2770 * <blockquote><pre>{@code 2771 MethodHandle invoker = MethodHandles.invoker(type); 2772 int spreadArgCount = type.parameterCount() - leadingArgCount; 2773 invoker = invoker.asSpreader(Object[].class, spreadArgCount); 2774 return invoker; 2775 * }</pre></blockquote> 2776 * This method throws no reflective or security exceptions. 2777 * @param type the desired target type 2778 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target 2779 * @return a method handle suitable for invoking any method handle of the given type 2780 * @throws NullPointerException if {@code type} is null 2781 * @throws IllegalArgumentException if {@code leadingArgCount} is not in 2782 * the range from 0 to {@code type.parameterCount()} inclusive, 2783 * or if the resulting method handle's type would have 2784 * <a href="MethodHandle.html#maxarity">too many parameters</a> 2785 */ 2786 static public spreadInvoker(MethodType type, int leadingArgCount)2787 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) { 2788 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount()) 2789 throw newIllegalArgumentException("bad argument count", leadingArgCount); 2790 2791 MethodHandle invoker = MethodHandles.invoker(type); 2792 int spreadArgCount = type.parameterCount() - leadingArgCount; 2793 invoker = invoker.asSpreader(Object[].class, spreadArgCount); 2794 return invoker; 2795 } 2796 2797 /** 2798 * Produces a special <em>invoker method handle</em> which can be used to 2799 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}. 2800 * The resulting invoker will have a type which is 2801 * exactly equal to the desired type, except that it will accept 2802 * an additional leading argument of type {@code MethodHandle}. 2803 * <p> 2804 * This method is equivalent to the following code (though it may be more efficient): 2805 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)} 2806 * 2807 * <p style="font-size:smaller;"> 2808 * <em>Discussion:</em> 2809 * Invoker method handles can be useful when working with variable method handles 2810 * of unknown types. 2811 * For example, to emulate an {@code invokeExact} call to a variable method 2812 * handle {@code M}, extract its type {@code T}, 2813 * look up the invoker method {@code X} for {@code T}, 2814 * and call the invoker method, as {@code X.invoke(T, A...)}. 2815 * (It would not work to call {@code X.invokeExact}, since the type {@code T} 2816 * is unknown.) 2817 * If spreading, collecting, or other argument transformations are required, 2818 * they can be applied once to the invoker {@code X} and reused on many {@code M} 2819 * method handle values, as long as they are compatible with the type of {@code X}. 2820 * <p style="font-size:smaller;"> 2821 * <em>(Note: The invoker method is not available via the Core Reflection API. 2822 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 2823 * on the declared {@code invokeExact} or {@code invoke} method will raise an 2824 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 2825 * <p> 2826 * This method throws no reflective or security exceptions. 2827 * @param type the desired target type 2828 * @return a method handle suitable for invoking any method handle of the given type 2829 * @throws IllegalArgumentException if the resulting method handle's type would have 2830 * <a href="MethodHandle.html#maxarity">too many parameters</a> 2831 */ 2832 static public exactInvoker(MethodType type)2833 MethodHandle exactInvoker(MethodType type) { 2834 return new Transformers.Invoker(type, true /* isExactInvoker */); 2835 } 2836 2837 /** 2838 * Produces a special <em>invoker method handle</em> which can be used to 2839 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}. 2840 * The resulting invoker will have a type which is 2841 * exactly equal to the desired type, except that it will accept 2842 * an additional leading argument of type {@code MethodHandle}. 2843 * <p> 2844 * Before invoking its target, if the target differs from the expected type, 2845 * the invoker will apply reference casts as 2846 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}. 2847 * Similarly, the return value will be converted as necessary. 2848 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle}, 2849 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}. 2850 * <p> 2851 * This method is equivalent to the following code (though it may be more efficient): 2852 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)} 2853 * <p style="font-size:smaller;"> 2854 * <em>Discussion:</em> 2855 * A {@linkplain MethodType#genericMethodType general method type} is one which 2856 * mentions only {@code Object} arguments and return values. 2857 * An invoker for such a type is capable of calling any method handle 2858 * of the same arity as the general type. 2859 * <p style="font-size:smaller;"> 2860 * <em>(Note: The invoker method is not available via the Core Reflection API. 2861 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 2862 * on the declared {@code invokeExact} or {@code invoke} method will raise an 2863 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 2864 * <p> 2865 * This method throws no reflective or security exceptions. 2866 * @param type the desired target type 2867 * @return a method handle suitable for invoking any method handle convertible to the given type 2868 * @throws IllegalArgumentException if the resulting method handle's type would have 2869 * <a href="MethodHandle.html#maxarity">too many parameters</a> 2870 */ 2871 static public invoker(MethodType type)2872 MethodHandle invoker(MethodType type) { 2873 return new Transformers.Invoker(type, false /* isExactInvoker */); 2874 } 2875 2876 // BEGIN Android-added: resolver for VarHandle accessor methods. methodHandleForVarHandleAccessor(VarHandle.AccessMode accessMode, MethodType type, boolean isExactInvoker)2877 static private MethodHandle methodHandleForVarHandleAccessor(VarHandle.AccessMode accessMode, 2878 MethodType type, 2879 boolean isExactInvoker) { 2880 Class<?> refc = VarHandle.class; 2881 Method method; 2882 try { 2883 method = refc.getDeclaredMethod(accessMode.methodName(), Object[].class); 2884 } catch (NoSuchMethodException e) { 2885 throw new InternalError("No method for AccessMode " + accessMode, e); 2886 } 2887 MethodType methodType = type.insertParameterTypes(0, VarHandle.class); 2888 int kind = isExactInvoker ? MethodHandle.INVOKE_VAR_HANDLE_EXACT 2889 : MethodHandle.INVOKE_VAR_HANDLE; 2890 return new MethodHandleImpl(method.getArtMethod(), kind, methodType); 2891 } 2892 // END Android-added: resolver for VarHandle accessor methods. 2893 2894 /** 2895 * Produces a special <em>invoker method handle</em> which can be used to 2896 * invoke a signature-polymorphic access mode method on any VarHandle whose 2897 * associated access mode type is compatible with the given type. 2898 * The resulting invoker will have a type which is exactly equal to the 2899 * desired given type, except that it will accept an additional leading 2900 * argument of type {@code VarHandle}. 2901 * 2902 * @param accessMode the VarHandle access mode 2903 * @param type the desired target type 2904 * @return a method handle suitable for invoking an access mode method of 2905 * any VarHandle whose access mode type is of the given type. 2906 * @since 9 2907 */ 2908 static public varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type)2909 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) { 2910 return methodHandleForVarHandleAccessor(accessMode, type, true /* isExactInvoker */); 2911 } 2912 2913 /** 2914 * Produces a special <em>invoker method handle</em> which can be used to 2915 * invoke a signature-polymorphic access mode method on any VarHandle whose 2916 * associated access mode type is compatible with the given type. 2917 * The resulting invoker will have a type which is exactly equal to the 2918 * desired given type, except that it will accept an additional leading 2919 * argument of type {@code VarHandle}. 2920 * <p> 2921 * Before invoking its target, if the access mode type differs from the 2922 * desired given type, the invoker will apply reference casts as necessary 2923 * and box, unbox, or widen primitive values, as if by 2924 * {@link MethodHandle#asType asType}. Similarly, the return value will be 2925 * converted as necessary. 2926 * <p> 2927 * This method is equivalent to the following code (though it may be more 2928 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)} 2929 * 2930 * @param accessMode the VarHandle access mode 2931 * @param type the desired target type 2932 * @return a method handle suitable for invoking an access mode method of 2933 * any VarHandle whose access mode type is convertible to the given 2934 * type. 2935 * @since 9 2936 */ 2937 static public varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type)2938 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) { 2939 return methodHandleForVarHandleAccessor(accessMode, type, false /* isExactInvoker */); 2940 } 2941 2942 // Android-changed: Basic invokers are not supported. 2943 // 2944 // static /*non-public*/ 2945 // MethodHandle basicInvoker(MethodType type) { 2946 // return type.invokers().basicInvoker(); 2947 // } 2948 2949 /// method handle modification (creation from other method handles) 2950 2951 /** 2952 * Produces a method handle which adapts the type of the 2953 * given method handle to a new type by pairwise argument and return type conversion. 2954 * The original type and new type must have the same number of arguments. 2955 * The resulting method handle is guaranteed to report a type 2956 * which is equal to the desired new type. 2957 * <p> 2958 * If the original type and new type are equal, returns target. 2959 * <p> 2960 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType}, 2961 * and some additional conversions are also applied if those conversions fail. 2962 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied 2963 * if possible, before or instead of any conversions done by {@code asType}: 2964 * <ul> 2965 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type, 2966 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast. 2967 * (This treatment of interfaces follows the usage of the bytecode verifier.) 2968 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive, 2969 * the boolean is converted to a byte value, 1 for true, 0 for false. 2970 * (This treatment follows the usage of the bytecode verifier.) 2971 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive, 2972 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5), 2973 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}. 2974 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean, 2975 * then a Java casting conversion (JLS 5.5) is applied. 2976 * (Specifically, <em>T0</em> will convert to <em>T1</em> by 2977 * widening and/or narrowing.) 2978 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing 2979 * conversion will be applied at runtime, possibly followed 2980 * by a Java casting conversion (JLS 5.5) on the primitive value, 2981 * possibly followed by a conversion from byte to boolean by testing 2982 * the low-order bit. 2983 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, 2984 * and if the reference is null at runtime, a zero value is introduced. 2985 * </ul> 2986 * @param target the method handle to invoke after arguments are retyped 2987 * @param newType the expected type of the new method handle 2988 * @return a method handle which delegates to the target after performing 2989 * any necessary argument conversions, and arranges for any 2990 * necessary return value conversions 2991 * @throws NullPointerException if either argument is null 2992 * @throws WrongMethodTypeException if the conversion cannot be made 2993 * @see MethodHandle#asType 2994 */ 2995 public static explicitCastArguments(MethodHandle target, MethodType newType)2996 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) { 2997 explicitCastArgumentsChecks(target, newType); 2998 // use the asTypeCache when possible: 2999 MethodType oldType = target.type(); 3000 if (oldType == newType) return target; 3001 if (oldType.explicitCastEquivalentToAsType(newType)) { 3002 if (Transformers.Transformer.class.isAssignableFrom(target.getClass())) { 3003 // The StackFrameReader and StackFrameWriter used to perform transforms on 3004 // EmulatedStackFrames (in Transformers.java) do not how to perform asType() 3005 // conversions, but we know here that an explicit cast transform is the same as 3006 // having called asType() on the method handle. 3007 return new Transformers.ExplicitCastArguments(target.asFixedArity(), newType); 3008 } else { 3009 // Runtime will perform asType() conversion during invocation. 3010 return target.asFixedArity().asType(newType); 3011 } 3012 } 3013 return new Transformers.ExplicitCastArguments(target, newType); 3014 } 3015 explicitCastArgumentsChecks(MethodHandle target, MethodType newType)3016 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) { 3017 if (target.type().parameterCount() != newType.parameterCount()) { 3018 throw new WrongMethodTypeException("cannot explicitly cast " + target + 3019 " to " + newType); 3020 } 3021 } 3022 3023 /** 3024 * Produces a method handle which adapts the calling sequence of the 3025 * given method handle to a new type, by reordering the arguments. 3026 * The resulting method handle is guaranteed to report a type 3027 * which is equal to the desired new type. 3028 * <p> 3029 * The given array controls the reordering. 3030 * Call {@code #I} the number of incoming parameters (the value 3031 * {@code newType.parameterCount()}, and call {@code #O} the number 3032 * of outgoing parameters (the value {@code target.type().parameterCount()}). 3033 * Then the length of the reordering array must be {@code #O}, 3034 * and each element must be a non-negative number less than {@code #I}. 3035 * For every {@code N} less than {@code #O}, the {@code N}-th 3036 * outgoing argument will be taken from the {@code I}-th incoming 3037 * argument, where {@code I} is {@code reorder[N]}. 3038 * <p> 3039 * No argument or return value conversions are applied. 3040 * The type of each incoming argument, as determined by {@code newType}, 3041 * must be identical to the type of the corresponding outgoing parameter 3042 * or parameters in the target method handle. 3043 * The return type of {@code newType} must be identical to the return 3044 * type of the original target. 3045 * <p> 3046 * The reordering array need not specify an actual permutation. 3047 * An incoming argument will be duplicated if its index appears 3048 * more than once in the array, and an incoming argument will be dropped 3049 * if its index does not appear in the array. 3050 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments}, 3051 * incoming arguments which are not mentioned in the reordering array 3052 * are may be any type, as determined only by {@code newType}. 3053 * <blockquote><pre>{@code 3054 import static java.lang.invoke.MethodHandles.*; 3055 import static java.lang.invoke.MethodType.*; 3056 ... 3057 MethodType intfn1 = methodType(int.class, int.class); 3058 MethodType intfn2 = methodType(int.class, int.class, int.class); 3059 MethodHandle sub = ... (int x, int y) -> (x-y) ...; 3060 assert(sub.type().equals(intfn2)); 3061 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1); 3062 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0); 3063 assert((int)rsub.invokeExact(1, 100) == 99); 3064 MethodHandle add = ... (int x, int y) -> (x+y) ...; 3065 assert(add.type().equals(intfn2)); 3066 MethodHandle twice = permuteArguments(add, intfn1, 0, 0); 3067 assert(twice.type().equals(intfn1)); 3068 assert((int)twice.invokeExact(21) == 42); 3069 * }</pre></blockquote> 3070 * @param target the method handle to invoke after arguments are reordered 3071 * @param newType the expected type of the new method handle 3072 * @param reorder an index array which controls the reordering 3073 * @return a method handle which delegates to the target after it 3074 * drops unused arguments and moves and/or duplicates the other arguments 3075 * @throws NullPointerException if any argument is null 3076 * @throws IllegalArgumentException if the index array length is not equal to 3077 * the arity of the target, or if any index array element 3078 * not a valid index for a parameter of {@code newType}, 3079 * or if two corresponding parameter types in 3080 * {@code target.type()} and {@code newType} are not identical, 3081 */ 3082 public static permuteArguments(MethodHandle target, MethodType newType, int... reorder)3083 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) { 3084 reorder = reorder.clone(); // get a private copy 3085 MethodType oldType = target.type(); 3086 permuteArgumentChecks(reorder, newType, oldType); 3087 3088 return new Transformers.PermuteArguments(newType, target, reorder); 3089 } 3090 3091 // Android-changed: findFirstDupOrDrop is unused and removed. 3092 // private static int findFirstDupOrDrop(int[] reorder, int newArity); 3093 permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType)3094 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) { 3095 if (newType.returnType() != oldType.returnType()) 3096 throw newIllegalArgumentException("return types do not match", 3097 oldType, newType); 3098 if (reorder.length == oldType.parameterCount()) { 3099 int limit = newType.parameterCount(); 3100 boolean bad = false; 3101 for (int j = 0; j < reorder.length; j++) { 3102 int i = reorder[j]; 3103 if (i < 0 || i >= limit) { 3104 bad = true; break; 3105 } 3106 Class<?> src = newType.parameterType(i); 3107 Class<?> dst = oldType.parameterType(j); 3108 if (src != dst) 3109 throw newIllegalArgumentException("parameter types do not match after reorder", 3110 oldType, newType); 3111 } 3112 if (!bad) return true; 3113 } 3114 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder)); 3115 } 3116 3117 /** 3118 * Produces a method handle of the requested return type which returns the given 3119 * constant value every time it is invoked. 3120 * <p> 3121 * Before the method handle is returned, the passed-in value is converted to the requested type. 3122 * If the requested type is primitive, widening primitive conversions are attempted, 3123 * else reference conversions are attempted. 3124 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}. 3125 * @param type the return type of the desired method handle 3126 * @param value the value to return 3127 * @return a method handle of the given return type and no arguments, which always returns the given value 3128 * @throws NullPointerException if the {@code type} argument is null 3129 * @throws ClassCastException if the value cannot be converted to the required return type 3130 * @throws IllegalArgumentException if the given type is {@code void.class} 3131 */ 3132 public static constant(Class<?> type, Object value)3133 MethodHandle constant(Class<?> type, Object value) { 3134 if (type.isPrimitive()) { 3135 if (type == void.class) 3136 throw newIllegalArgumentException("void type"); 3137 Wrapper w = Wrapper.forPrimitiveType(type); 3138 value = w.convert(value, type); 3139 if (w.zero().equals(value)) 3140 return zero(w, type); 3141 return insertArguments(identity(type), 0, value); 3142 } else { 3143 if (value == null) 3144 return zero(Wrapper.OBJECT, type); 3145 return identity(type).bindTo(value); 3146 } 3147 } 3148 3149 /** 3150 * Produces a method handle which returns its sole argument when invoked. 3151 * @param type the type of the sole parameter and return value of the desired method handle 3152 * @return a unary method handle which accepts and returns the given type 3153 * @throws NullPointerException if the argument is null 3154 * @throws IllegalArgumentException if the given type is {@code void.class} 3155 */ 3156 public static identity(Class<?> type)3157 MethodHandle identity(Class<?> type) { 3158 // Android-added: explicit non-null check. 3159 Objects.requireNonNull(type); 3160 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT); 3161 int pos = btw.ordinal(); 3162 MethodHandle ident = IDENTITY_MHS[pos]; 3163 if (ident == null) { 3164 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType())); 3165 } 3166 if (ident.type().returnType() == type) 3167 return ident; 3168 // something like identity(Foo.class); do not bother to intern these 3169 assert (btw == Wrapper.OBJECT); 3170 return makeIdentity(type); 3171 } 3172 3173 /** 3174 * Produces a constant method handle of the requested return type which 3175 * returns the default value for that type every time it is invoked. 3176 * The resulting constant method handle will have no side effects. 3177 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}. 3178 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))}, 3179 * since {@code explicitCastArguments} converts {@code null} to default values. 3180 * @param type the expected return type of the desired method handle 3181 * @return a constant method handle that takes no arguments 3182 * and returns the default value of the given type (or void, if the type is void) 3183 * @throws NullPointerException if the argument is null 3184 * @see MethodHandles#constant 3185 * @see MethodHandles#empty 3186 * @see MethodHandles#explicitCastArguments 3187 * @since 9 3188 */ zero(Class<?> type)3189 public static MethodHandle zero(Class<?> type) { 3190 Objects.requireNonNull(type); 3191 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type); 3192 } 3193 identityOrVoid(Class<?> type)3194 private static MethodHandle identityOrVoid(Class<?> type) { 3195 return type == void.class ? zero(type) : identity(type); 3196 } 3197 3198 /** 3199 * Produces a method handle of the requested type which ignores any arguments, does nothing, 3200 * and returns a suitable default depending on the return type. 3201 * That is, it returns a zero primitive value, a {@code null}, or {@code void}. 3202 * <p>The returned method handle is equivalent to 3203 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}. 3204 * 3205 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as 3206 * {@code guardWithTest(pred, target, empty(target.type())}. 3207 * @param type the type of the desired method handle 3208 * @return a constant method handle of the given type, which returns a default value of the given return type 3209 * @throws NullPointerException if the argument is null 3210 * @see MethodHandles#zero 3211 * @see MethodHandles#constant 3212 * @since 9 3213 */ empty(MethodType type)3214 public static MethodHandle empty(MethodType type) { 3215 Objects.requireNonNull(type); 3216 return dropArguments(zero(type.returnType()), 0, type.parameterList()); 3217 } 3218 3219 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT]; makeIdentity(Class<?> ptype)3220 private static MethodHandle makeIdentity(Class<?> ptype) { 3221 // Android-changed: Android implementation using identity() functions and transformers. 3222 // MethodType mtype = methodType(ptype, ptype); 3223 // LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype)); 3224 // return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY); 3225 if (ptype.isPrimitive()) { 3226 try { 3227 final MethodType mt = methodType(ptype, ptype); 3228 return Lookup.PUBLIC_LOOKUP.findStatic(MethodHandles.class, "identity", mt); 3229 } catch (NoSuchMethodException | IllegalAccessException e) { 3230 throw new AssertionError(e); 3231 } 3232 } else { 3233 return new Transformers.ReferenceIdentity(ptype); 3234 } 3235 } 3236 3237 // Android-added: helper methods for identity(). identity(byte val)3238 /** @hide */ public static byte identity(byte val) { return val; } identity(boolean val)3239 /** @hide */ public static boolean identity(boolean val) { return val; } identity(char val)3240 /** @hide */ public static char identity(char val) { return val; } identity(short val)3241 /** @hide */ public static short identity(short val) { return val; } identity(int val)3242 /** @hide */ public static int identity(int val) { return val; } identity(long val)3243 /** @hide */ public static long identity(long val) { return val; } identity(float val)3244 /** @hide */ public static float identity(float val) { return val; } identity(double val)3245 /** @hide */ public static double identity(double val) { return val; } 3246 zero(Wrapper btw, Class<?> rtype)3247 private static MethodHandle zero(Wrapper btw, Class<?> rtype) { 3248 int pos = btw.ordinal(); 3249 MethodHandle zero = ZERO_MHS[pos]; 3250 if (zero == null) { 3251 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType())); 3252 } 3253 if (zero.type().returnType() == rtype) 3254 return zero; 3255 assert(btw == Wrapper.OBJECT); 3256 return makeZero(rtype); 3257 } 3258 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT]; makeZero(Class<?> rtype)3259 private static MethodHandle makeZero(Class<?> rtype) { 3260 // Android-changed: use Android specific implementation. 3261 // MethodType mtype = methodType(rtype); 3262 // LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype)); 3263 // return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO); 3264 return new Transformers.ZeroValue(rtype); 3265 } 3266 setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value)3267 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) { 3268 // Simulate a CAS, to avoid racy duplication of results. 3269 MethodHandle prev = cache[pos]; 3270 if (prev != null) return prev; 3271 return cache[pos] = value; 3272 } 3273 3274 /** 3275 * Provides a target method handle with one or more <em>bound arguments</em> 3276 * in advance of the method handle's invocation. 3277 * The formal parameters to the target corresponding to the bound 3278 * arguments are called <em>bound parameters</em>. 3279 * Returns a new method handle which saves away the bound arguments. 3280 * When it is invoked, it receives arguments for any non-bound parameters, 3281 * binds the saved arguments to their corresponding parameters, 3282 * and calls the original target. 3283 * <p> 3284 * The type of the new method handle will drop the types for the bound 3285 * parameters from the original target type, since the new method handle 3286 * will no longer require those arguments to be supplied by its callers. 3287 * <p> 3288 * Each given argument object must match the corresponding bound parameter type. 3289 * If a bound parameter type is a primitive, the argument object 3290 * must be a wrapper, and will be unboxed to produce the primitive value. 3291 * <p> 3292 * The {@code pos} argument selects which parameters are to be bound. 3293 * It may range between zero and <i>N-L</i> (inclusively), 3294 * where <i>N</i> is the arity of the target method handle 3295 * and <i>L</i> is the length of the values array. 3296 * @param target the method handle to invoke after the argument is inserted 3297 * @param pos where to insert the argument (zero for the first) 3298 * @param values the series of arguments to insert 3299 * @return a method handle which inserts an additional argument, 3300 * before calling the original method handle 3301 * @throws NullPointerException if the target or the {@code values} array is null 3302 * @see MethodHandle#bindTo 3303 */ 3304 public static insertArguments(MethodHandle target, int pos, Object... values)3305 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) { 3306 int insCount = values.length; 3307 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos); 3308 if (insCount == 0) { 3309 return target; 3310 } 3311 3312 // Throw ClassCastExceptions early if we can't cast any of the provided values 3313 // to the required type. 3314 for (int i = 0; i < insCount; i++) { 3315 final Class<?> ptype = ptypes[pos + i]; 3316 if (!ptype.isPrimitive()) { 3317 ptypes[pos + i].cast(values[i]); 3318 } else { 3319 // Will throw a ClassCastException if something terrible happens. 3320 values[i] = Wrapper.forPrimitiveType(ptype).convert(values[i], ptype); 3321 } 3322 } 3323 3324 return new Transformers.InsertArguments(target, pos, values); 3325 } 3326 3327 // Android-changed: insertArgumentPrimitive is unused. 3328 // 3329 // private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos, 3330 // Class<?> ptype, Object value) { 3331 // Wrapper w = Wrapper.forPrimitiveType(ptype); 3332 // // perform unboxing and/or primitive conversion 3333 // value = w.convert(value, ptype); 3334 // switch (w) { 3335 // case INT: return result.bindArgumentI(pos, (int)value); 3336 // case LONG: return result.bindArgumentJ(pos, (long)value); 3337 // case FLOAT: return result.bindArgumentF(pos, (float)value); 3338 // case DOUBLE: return result.bindArgumentD(pos, (double)value); 3339 // default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value)); 3340 // } 3341 // } 3342 insertArgumentsChecks(MethodHandle target, int insCount, int pos)3343 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException { 3344 MethodType oldType = target.type(); 3345 int outargs = oldType.parameterCount(); 3346 int inargs = outargs - insCount; 3347 if (inargs < 0) 3348 throw newIllegalArgumentException("too many values to insert"); 3349 if (pos < 0 || pos > inargs) 3350 throw newIllegalArgumentException("no argument type to append"); 3351 return oldType.ptypes(); 3352 } 3353 3354 // Android-changed: inclusive language preference for 'placeholder'. 3355 /** 3356 * Produces a method handle which will discard some placeholder arguments 3357 * before calling some other specified <i>target</i> method handle. 3358 * The type of the new method handle will be the same as the target's type, 3359 * except it will also include the placeholder argument types, 3360 * at some given position. 3361 * <p> 3362 * The {@code pos} argument may range between zero and <i>N</i>, 3363 * where <i>N</i> is the arity of the target. 3364 * If {@code pos} is zero, the placeholder arguments will precede 3365 * the target's real arguments; if {@code pos} is <i>N</i> 3366 * they will come after. 3367 * <p> 3368 * <b>Example:</b> 3369 * <blockquote><pre>{@code 3370 import static java.lang.invoke.MethodHandles.*; 3371 import static java.lang.invoke.MethodType.*; 3372 ... 3373 MethodHandle cat = lookup().findVirtual(String.class, 3374 "concat", methodType(String.class, String.class)); 3375 assertEquals("xy", (String) cat.invokeExact("x", "y")); 3376 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class); 3377 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2)); 3378 assertEquals(bigType, d0.type()); 3379 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z")); 3380 * }</pre></blockquote> 3381 * <p> 3382 * This method is also equivalent to the following code: 3383 * <blockquote><pre> 3384 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))} 3385 * </pre></blockquote> 3386 * @param target the method handle to invoke after the arguments are dropped 3387 * @param valueTypes the type(s) of the argument(s) to drop 3388 * @param pos position of first argument to drop (zero for the leftmost) 3389 * @return a method handle which drops arguments of the given types, 3390 * before calling the original method handle 3391 * @throws NullPointerException if the target is null, 3392 * or if the {@code valueTypes} list or any of its elements is null 3393 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 3394 * or if {@code pos} is negative or greater than the arity of the target, 3395 * or if the new method handle's type would have too many parameters 3396 */ 3397 public static dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes)3398 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) { 3399 return dropArguments0(target, pos, copyTypes(valueTypes.toArray())); 3400 } 3401 copyTypes(Object[] array)3402 private static List<Class<?>> copyTypes(Object[] array) { 3403 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class)); 3404 } 3405 3406 private static dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes)3407 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) { 3408 MethodType oldType = target.type(); // get NPE 3409 int dropped = dropArgumentChecks(oldType, pos, valueTypes); 3410 MethodType newType = oldType.insertParameterTypes(pos, valueTypes); 3411 if (dropped == 0) return target; 3412 // Android-changed: transformer implementation. 3413 // BoundMethodHandle result = target.rebind(); 3414 // LambdaForm lform = result.form; 3415 // int insertFormArg = 1 + pos; 3416 // for (Class<?> ptype : valueTypes) { 3417 // lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype)); 3418 // } 3419 // result = result.copyWith(newType, lform); 3420 // return result; 3421 return new Transformers.DropArguments(newType, target, pos, dropped); 3422 } 3423 dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes)3424 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) { 3425 int dropped = valueTypes.size(); 3426 MethodType.checkSlotCount(dropped); 3427 int outargs = oldType.parameterCount(); 3428 int inargs = outargs + dropped; 3429 if (pos < 0 || pos > outargs) 3430 throw newIllegalArgumentException("no argument type to remove" 3431 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs) 3432 ); 3433 return dropped; 3434 } 3435 3436 // Android-changed: inclusive language preference for 'placeholder'. 3437 /** 3438 * Produces a method handle which will discard some placeholder arguments 3439 * before calling some other specified <i>target</i> method handle. 3440 * The type of the new method handle will be the same as the target's type, 3441 * except it will also include the placeholder argument types, 3442 * at some given position. 3443 * <p> 3444 * The {@code pos} argument may range between zero and <i>N</i>, 3445 * where <i>N</i> is the arity of the target. 3446 * If {@code pos} is zero, the placeholder arguments will precede 3447 * the target's real arguments; if {@code pos} is <i>N</i> 3448 * they will come after. 3449 * @apiNote 3450 * <blockquote><pre>{@code 3451 import static java.lang.invoke.MethodHandles.*; 3452 import static java.lang.invoke.MethodType.*; 3453 ... 3454 MethodHandle cat = lookup().findVirtual(String.class, 3455 "concat", methodType(String.class, String.class)); 3456 assertEquals("xy", (String) cat.invokeExact("x", "y")); 3457 MethodHandle d0 = dropArguments(cat, 0, String.class); 3458 assertEquals("yz", (String) d0.invokeExact("x", "y", "z")); 3459 MethodHandle d1 = dropArguments(cat, 1, String.class); 3460 assertEquals("xz", (String) d1.invokeExact("x", "y", "z")); 3461 MethodHandle d2 = dropArguments(cat, 2, String.class); 3462 assertEquals("xy", (String) d2.invokeExact("x", "y", "z")); 3463 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class); 3464 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z")); 3465 * }</pre></blockquote> 3466 * <p> 3467 * This method is also equivalent to the following code: 3468 * <blockquote><pre> 3469 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))} 3470 * </pre></blockquote> 3471 * @param target the method handle to invoke after the arguments are dropped 3472 * @param valueTypes the type(s) of the argument(s) to drop 3473 * @param pos position of first argument to drop (zero for the leftmost) 3474 * @return a method handle which drops arguments of the given types, 3475 * before calling the original method handle 3476 * @throws NullPointerException if the target is null, 3477 * or if the {@code valueTypes} array or any of its elements is null 3478 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 3479 * or if {@code pos} is negative or greater than the arity of the target, 3480 * or if the new method handle's type would have 3481 * <a href="MethodHandle.html#maxarity">too many parameters</a> 3482 */ 3483 public static dropArguments(MethodHandle target, int pos, Class<?>... valueTypes)3484 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) { 3485 return dropArguments0(target, pos, copyTypes(valueTypes)); 3486 } 3487 3488 // private version which allows caller some freedom with error handling dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos, boolean nullOnFailure)3489 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos, 3490 boolean nullOnFailure) { 3491 newTypes = copyTypes(newTypes.toArray()); 3492 List<Class<?>> oldTypes = target.type().parameterList(); 3493 int match = oldTypes.size(); 3494 if (skip != 0) { 3495 if (skip < 0 || skip > match) { 3496 throw newIllegalArgumentException("illegal skip", skip, target); 3497 } 3498 oldTypes = oldTypes.subList(skip, match); 3499 match -= skip; 3500 } 3501 List<Class<?>> addTypes = newTypes; 3502 int add = addTypes.size(); 3503 if (pos != 0) { 3504 if (pos < 0 || pos > add) { 3505 throw newIllegalArgumentException("illegal pos", pos, newTypes); 3506 } 3507 addTypes = addTypes.subList(pos, add); 3508 add -= pos; 3509 assert(addTypes.size() == add); 3510 } 3511 // Do not add types which already match the existing arguments. 3512 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) { 3513 if (nullOnFailure) { 3514 return null; 3515 } 3516 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes); 3517 } 3518 addTypes = addTypes.subList(match, add); 3519 add -= match; 3520 assert(addTypes.size() == add); 3521 // newTypes: ( P*[pos], M*[match], A*[add] ) 3522 // target: ( S*[skip], M*[match] ) 3523 MethodHandle adapter = target; 3524 if (add > 0) { 3525 adapter = dropArguments0(adapter, skip+ match, addTypes); 3526 } 3527 // adapter: (S*[skip], M*[match], A*[add] ) 3528 if (pos > 0) { 3529 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos)); 3530 } 3531 // adapter: (S*[skip], P*[pos], M*[match], A*[add] ) 3532 return adapter; 3533 } 3534 3535 // Android-changed: inclusive language preference for 'placeholder'. 3536 /** 3537 * Adapts a target method handle to match the given parameter type list. If necessary, adds placeholder arguments. Some 3538 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter 3539 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The 3540 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before 3541 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by 3542 * {@link #dropArguments(MethodHandle, int, Class[])}. 3543 * <p> 3544 * The resulting handle will have the same return type as the target handle. 3545 * <p> 3546 * In more formal terms, assume these two type lists:<ul> 3547 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as 3548 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list, 3549 * {@code newTypes}. 3550 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as 3551 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's 3552 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching 3553 * sub-list. 3554 * </ul> 3555 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type 3556 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by 3557 * {@link #dropArguments(MethodHandle, int, Class[])}. 3558 * 3559 * @apiNote 3560 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be 3561 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows: 3562 * <blockquote><pre>{@code 3563 import static java.lang.invoke.MethodHandles.*; 3564 import static java.lang.invoke.MethodType.*; 3565 ... 3566 ... 3567 MethodHandle h0 = constant(boolean.class, true); 3568 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class)); 3569 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class); 3570 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList()); 3571 if (h1.type().parameterCount() < h2.type().parameterCount()) 3572 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1 3573 else 3574 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2 3575 MethodHandle h3 = guardWithTest(h0, h1, h2); 3576 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c")); 3577 * }</pre></blockquote> 3578 * @param target the method handle to adapt 3579 * @param skip number of targets parameters to disregard (they will be unchanged) 3580 * @param newTypes the list of types to match {@code target}'s parameter type list to 3581 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur 3582 * @return a possibly adapted method handle 3583 * @throws NullPointerException if either argument is null 3584 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class}, 3585 * or if {@code skip} is negative or greater than the arity of the target, 3586 * or if {@code pos} is negative or greater than the newTypes list size, 3587 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position 3588 * {@code pos}. 3589 * @since 9 3590 */ 3591 public static dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos)3592 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) { 3593 Objects.requireNonNull(target); 3594 Objects.requireNonNull(newTypes); 3595 return dropArgumentsToMatch(target, skip, newTypes, pos, false); 3596 } 3597 3598 /** 3599 * Drop the return value of the target handle (if any). 3600 * The returned method handle will have a {@code void} return type. 3601 * 3602 * @param target the method handle to adapt 3603 * @return a possibly adapted method handle 3604 * @throws NullPointerException if {@code target} is null 3605 * @since 16 3606 */ dropReturn(MethodHandle target)3607 public static MethodHandle dropReturn(MethodHandle target) { 3608 Objects.requireNonNull(target); 3609 MethodType oldType = target.type(); 3610 Class<?> oldReturnType = oldType.returnType(); 3611 if (oldReturnType == void.class) 3612 return target; 3613 3614 MethodType newType = oldType.changeReturnType(void.class); 3615 // Android-changed: no support for BoundMethodHandle or LambdaForm. 3616 // BoundMethodHandle result = target.rebind(); 3617 // LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true); 3618 // result = result.copyWith(newType, lform); 3619 // return result; 3620 return target.asType(newType); 3621 } 3622 3623 /** 3624 * Adapts a target method handle by pre-processing 3625 * one or more of its arguments, each with its own unary filter function, 3626 * and then calling the target with each pre-processed argument 3627 * replaced by the result of its corresponding filter function. 3628 * <p> 3629 * The pre-processing is performed by one or more method handles, 3630 * specified in the elements of the {@code filters} array. 3631 * The first element of the filter array corresponds to the {@code pos} 3632 * argument of the target, and so on in sequence. 3633 * The filter functions are invoked in left to right order. 3634 * <p> 3635 * Null arguments in the array are treated as identity functions, 3636 * and the corresponding arguments left unchanged. 3637 * (If there are no non-null elements in the array, the original target is returned.) 3638 * Each filter is applied to the corresponding argument of the adapter. 3639 * <p> 3640 * If a filter {@code F} applies to the {@code N}th argument of 3641 * the target, then {@code F} must be a method handle which 3642 * takes exactly one argument. The type of {@code F}'s sole argument 3643 * replaces the corresponding argument type of the target 3644 * in the resulting adapted method handle. 3645 * The return type of {@code F} must be identical to the corresponding 3646 * parameter type of the target. 3647 * <p> 3648 * It is an error if there are elements of {@code filters} 3649 * (null or not) 3650 * which do not correspond to argument positions in the target. 3651 * <p><b>Example:</b> 3652 * <blockquote><pre>{@code 3653 import static java.lang.invoke.MethodHandles.*; 3654 import static java.lang.invoke.MethodType.*; 3655 ... 3656 MethodHandle cat = lookup().findVirtual(String.class, 3657 "concat", methodType(String.class, String.class)); 3658 MethodHandle upcase = lookup().findVirtual(String.class, 3659 "toUpperCase", methodType(String.class)); 3660 assertEquals("xy", (String) cat.invokeExact("x", "y")); 3661 MethodHandle f0 = filterArguments(cat, 0, upcase); 3662 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy 3663 MethodHandle f1 = filterArguments(cat, 1, upcase); 3664 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY 3665 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase); 3666 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY 3667 * }</pre></blockquote> 3668 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 3669 * denotes the return type of both the {@code target} and resulting adapter. 3670 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values 3671 * of the parameters and arguments that precede and follow the filter position 3672 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and 3673 * values of the filtered parameters and arguments; they also represent the 3674 * return types of the {@code filter[i]} handles. The latter accept arguments 3675 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of 3676 * the resulting adapter. 3677 * <blockquote><pre>{@code 3678 * T target(P... p, A[i]... a[i], B... b); 3679 * A[i] filter[i](V[i]); 3680 * T adapter(P... p, V[i]... v[i], B... b) { 3681 * return target(p..., filter[i](v[i])..., b...); 3682 * } 3683 * }</pre></blockquote> 3684 * <p> 3685 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 3686 * variable-arity method handle}, even if the original target method handle was. 3687 * 3688 * @param target the method handle to invoke after arguments are filtered 3689 * @param pos the position of the first argument to filter 3690 * @param filters method handles to call initially on filtered arguments 3691 * @return method handle which incorporates the specified argument filtering logic 3692 * @throws NullPointerException if the target is null 3693 * or if the {@code filters} array is null 3694 * @throws IllegalArgumentException if a non-null element of {@code filters} 3695 * does not match a corresponding argument type of target as described above, 3696 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}, 3697 * or if the resulting method handle's type would have 3698 * <a href="MethodHandle.html#maxarity">too many parameters</a> 3699 */ 3700 public static filterArguments(MethodHandle target, int pos, MethodHandle... filters)3701 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) { 3702 filterArgumentsCheckArity(target, pos, filters); 3703 MethodHandle adapter = target; 3704 // Android-changed: transformer implementation. 3705 // process filters in reverse order so that the invocation of 3706 // the resulting adapter will invoke the filters in left-to-right order 3707 // for (int i = filters.length - 1; i >= 0; --i) { 3708 // MethodHandle filter = filters[i]; 3709 // if (filter == null) continue; // ignore null elements of filters 3710 // adapter = filterArgument(adapter, pos + i, filter); 3711 // } 3712 // return adapter; 3713 boolean hasNonNullFilter = false; 3714 for (int i = 0; i < filters.length; ++i) { 3715 MethodHandle filter = filters[i]; 3716 if (filter != null) { 3717 hasNonNullFilter = true; 3718 filterArgumentChecks(target, i + pos, filter); 3719 } 3720 } 3721 if (!hasNonNullFilter) { 3722 return target; 3723 } 3724 return new Transformers.FilterArguments(target, pos, filters); 3725 } 3726 3727 /*non-public*/ static filterArgument(MethodHandle target, int pos, MethodHandle filter)3728 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) { 3729 filterArgumentChecks(target, pos, filter); 3730 // Android-changed: use Transformer implementation. 3731 // MethodType targetType = target.type(); 3732 // MethodType filterType = filter.type(); 3733 // BoundMethodHandle result = target.rebind(); 3734 // Class<?> newParamType = filterType.parameterType(0); 3735 // LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType)); 3736 // MethodType newType = targetType.changeParameterType(pos, newParamType); 3737 // result = result.copyWithExtendL(newType, lform, filter); 3738 // return result; 3739 return new Transformers.FilterArguments(target, pos, filter); 3740 } 3741 filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters)3742 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) { 3743 MethodType targetType = target.type(); 3744 int maxPos = targetType.parameterCount(); 3745 if (pos + filters.length > maxPos) 3746 throw newIllegalArgumentException("too many filters"); 3747 } 3748 filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter)3749 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 3750 MethodType targetType = target.type(); 3751 MethodType filterType = filter.type(); 3752 if (filterType.parameterCount() != 1 3753 || filterType.returnType() != targetType.parameterType(pos)) 3754 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 3755 } 3756 3757 /** 3758 * Adapts a target method handle by pre-processing 3759 * a sub-sequence of its arguments with a filter (another method handle). 3760 * The pre-processed arguments are replaced by the result (if any) of the 3761 * filter function. 3762 * The target is then called on the modified (usually shortened) argument list. 3763 * <p> 3764 * If the filter returns a value, the target must accept that value as 3765 * its argument in position {@code pos}, preceded and/or followed by 3766 * any arguments not passed to the filter. 3767 * If the filter returns void, the target must accept all arguments 3768 * not passed to the filter. 3769 * No arguments are reordered, and a result returned from the filter 3770 * replaces (in order) the whole subsequence of arguments originally 3771 * passed to the adapter. 3772 * <p> 3773 * The argument types (if any) of the filter 3774 * replace zero or one argument types of the target, at position {@code pos}, 3775 * in the resulting adapted method handle. 3776 * The return type of the filter (if any) must be identical to the 3777 * argument type of the target at position {@code pos}, and that target argument 3778 * is supplied by the return value of the filter. 3779 * <p> 3780 * In all cases, {@code pos} must be greater than or equal to zero, and 3781 * {@code pos} must also be less than or equal to the target's arity. 3782 * <p><b>Example:</b> 3783 * <blockquote><pre>{@code 3784 import static java.lang.invoke.MethodHandles.*; 3785 import static java.lang.invoke.MethodType.*; 3786 ... 3787 MethodHandle deepToString = publicLookup() 3788 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); 3789 3790 MethodHandle ts1 = deepToString.asCollector(String[].class, 1); 3791 assertEquals("[strange]", (String) ts1.invokeExact("strange")); 3792 3793 MethodHandle ts2 = deepToString.asCollector(String[].class, 2); 3794 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down")); 3795 3796 MethodHandle ts3 = deepToString.asCollector(String[].class, 3); 3797 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2); 3798 assertEquals("[top, [up, down], strange]", 3799 (String) ts3_ts2.invokeExact("top", "up", "down", "strange")); 3800 3801 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1); 3802 assertEquals("[top, [up, down], [strange]]", 3803 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange")); 3804 3805 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3); 3806 assertEquals("[top, [[up, down, strange], charm], bottom]", 3807 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom")); 3808 * }</pre></blockquote> 3809 * <p> Here is pseudocode for the resulting adapter: 3810 * <blockquote><pre>{@code 3811 * T target(A...,V,C...); 3812 * V filter(B...); 3813 * T adapter(A... a,B... b,C... c) { 3814 * V v = filter(b...); 3815 * return target(a...,v,c...); 3816 * } 3817 * // and if the filter has no arguments: 3818 * T target2(A...,V,C...); 3819 * V filter2(); 3820 * T adapter2(A... a,C... c) { 3821 * V v = filter2(); 3822 * return target2(a...,v,c...); 3823 * } 3824 * // and if the filter has a void return: 3825 * T target3(A...,C...); 3826 * void filter3(B...); 3827 * void adapter3(A... a,B... b,C... c) { 3828 * filter3(b...); 3829 * return target3(a...,c...); 3830 * } 3831 * }</pre></blockquote> 3832 * <p> 3833 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to 3834 * one which first "folds" the affected arguments, and then drops them, in separate 3835 * steps as follows: 3836 * <blockquote><pre>{@code 3837 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2 3838 * mh = MethodHandles.foldArguments(mh, coll); //step 1 3839 * }</pre></blockquote> 3840 * If the target method handle consumes no arguments besides than the result 3841 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)} 3842 * is equivalent to {@code filterReturnValue(coll, mh)}. 3843 * If the filter method handle {@code coll} consumes one argument and produces 3844 * a non-void result, then {@code collectArguments(mh, N, coll)} 3845 * is equivalent to {@code filterArguments(mh, N, coll)}. 3846 * Other equivalences are possible but would require argument permutation. 3847 * 3848 * @param target the method handle to invoke after filtering the subsequence of arguments 3849 * @param pos the position of the first adapter argument to pass to the filter, 3850 * and/or the target argument which receives the result of the filter 3851 * @param filter method handle to call on the subsequence of arguments 3852 * @return method handle which incorporates the specified argument subsequence filtering logic 3853 * @throws NullPointerException if either argument is null 3854 * @throws IllegalArgumentException if the return type of {@code filter} 3855 * is non-void and is not the same as the {@code pos} argument of the target, 3856 * or if {@code pos} is not between 0 and the target's arity, inclusive, 3857 * or if the resulting method handle's type would have 3858 * <a href="MethodHandle.html#maxarity">too many parameters</a> 3859 * @see MethodHandles#foldArguments 3860 * @see MethodHandles#filterArguments 3861 * @see MethodHandles#filterReturnValue 3862 */ 3863 public static collectArguments(MethodHandle target, int pos, MethodHandle filter)3864 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) { 3865 MethodType newType = collectArgumentsChecks(target, pos, filter); 3866 return new Transformers.CollectArguments(target, filter, pos, newType); 3867 } 3868 collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter)3869 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 3870 MethodType targetType = target.type(); 3871 MethodType filterType = filter.type(); 3872 Class<?> rtype = filterType.returnType(); 3873 Class<?>[] filterArgs = filterType.ptypes(); 3874 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) || 3875 (rtype != void.class && pos >= targetType.parameterCount())) { 3876 throw newIllegalArgumentException("position is out of range for target", target, pos); 3877 } 3878 if (rtype == void.class) { 3879 return targetType.insertParameterTypes(pos, filterArgs); 3880 } 3881 if (rtype != targetType.parameterType(pos)) { 3882 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 3883 } 3884 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs); 3885 } 3886 3887 /** 3888 * Adapts a target method handle by post-processing 3889 * its return value (if any) with a filter (another method handle). 3890 * The result of the filter is returned from the adapter. 3891 * <p> 3892 * If the target returns a value, the filter must accept that value as 3893 * its only argument. 3894 * If the target returns void, the filter must accept no arguments. 3895 * <p> 3896 * The return type of the filter 3897 * replaces the return type of the target 3898 * in the resulting adapted method handle. 3899 * The argument type of the filter (if any) must be identical to the 3900 * return type of the target. 3901 * <p><b>Example:</b> 3902 * <blockquote><pre>{@code 3903 import static java.lang.invoke.MethodHandles.*; 3904 import static java.lang.invoke.MethodType.*; 3905 ... 3906 MethodHandle cat = lookup().findVirtual(String.class, 3907 "concat", methodType(String.class, String.class)); 3908 MethodHandle length = lookup().findVirtual(String.class, 3909 "length", methodType(int.class)); 3910 System.out.println((String) cat.invokeExact("x", "y")); // xy 3911 MethodHandle f0 = filterReturnValue(cat, length); 3912 System.out.println((int) f0.invokeExact("x", "y")); // 2 3913 * }</pre></blockquote> 3914 * <p>Here is pseudocode for the resulting adapter. In the code, 3915 * {@code T}/{@code t} represent the result type and value of the 3916 * {@code target}; {@code V}, the result type of the {@code filter}; and 3917 * {@code A}/{@code a}, the types and values of the parameters and arguments 3918 * of the {@code target} as well as the resulting adapter. 3919 * <blockquote><pre>{@code 3920 * T target(A...); 3921 * V filter(T); 3922 * V adapter(A... a) { 3923 * T t = target(a...); 3924 * return filter(t); 3925 * } 3926 * // and if the target has a void return: 3927 * void target2(A...); 3928 * V filter2(); 3929 * V adapter2(A... a) { 3930 * target2(a...); 3931 * return filter2(); 3932 * } 3933 * // and if the filter has a void return: 3934 * T target3(A...); 3935 * void filter3(V); 3936 * void adapter3(A... a) { 3937 * T t = target3(a...); 3938 * filter3(t); 3939 * } 3940 * }</pre></blockquote> 3941 * <p> 3942 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 3943 * variable-arity method handle}, even if the original target method handle was. 3944 * @param target the method handle to invoke before filtering the return value 3945 * @param filter method handle to call on the return value 3946 * @return method handle which incorporates the specified return value filtering logic 3947 * @throws NullPointerException if either argument is null 3948 * @throws IllegalArgumentException if the argument list of {@code filter} 3949 * does not match the return type of target as described above 3950 */ 3951 public static filterReturnValue(MethodHandle target, MethodHandle filter)3952 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) { 3953 MethodType targetType = target.type(); 3954 MethodType filterType = filter.type(); 3955 filterReturnValueChecks(targetType, filterType); 3956 // Android-changed: use a transformer. 3957 // BoundMethodHandle result = target.rebind(); 3958 // BasicType rtype = BasicType.basicType(filterType.returnType()); 3959 // LambdaForm lform = result.editor().filterReturnForm(rtype, false); 3960 // MethodType newType = targetType.changeReturnType(filterType.returnType()); 3961 // result = result.copyWithExtendL(newType, lform, filter); 3962 // return result; 3963 return new Transformers.FilterReturnValue(target, filter); 3964 } 3965 filterReturnValueChecks(MethodType targetType, MethodType filterType)3966 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException { 3967 Class<?> rtype = targetType.returnType(); 3968 int filterValues = filterType.parameterCount(); 3969 if (filterValues == 0 3970 ? (rtype != void.class) 3971 : (rtype != filterType.parameterType(0) || filterValues != 1)) 3972 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 3973 } 3974 3975 /** 3976 * Adapts a target method handle by pre-processing 3977 * some of its arguments, and then calling the target with 3978 * the result of the pre-processing, inserted into the original 3979 * sequence of arguments. 3980 * <p> 3981 * The pre-processing is performed by {@code combiner}, a second method handle. 3982 * Of the arguments passed to the adapter, the first {@code N} arguments 3983 * are copied to the combiner, which is then called. 3984 * (Here, {@code N} is defined as the parameter count of the combiner.) 3985 * After this, control passes to the target, with any result 3986 * from the combiner inserted before the original {@code N} incoming 3987 * arguments. 3988 * <p> 3989 * If the combiner returns a value, the first parameter type of the target 3990 * must be identical with the return type of the combiner, and the next 3991 * {@code N} parameter types of the target must exactly match the parameters 3992 * of the combiner. 3993 * <p> 3994 * If the combiner has a void return, no result will be inserted, 3995 * and the first {@code N} parameter types of the target 3996 * must exactly match the parameters of the combiner. 3997 * <p> 3998 * The resulting adapter is the same type as the target, except that the 3999 * first parameter type is dropped, 4000 * if it corresponds to the result of the combiner. 4001 * <p> 4002 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments 4003 * that either the combiner or the target does not wish to receive. 4004 * If some of the incoming arguments are destined only for the combiner, 4005 * consider using {@link MethodHandle#asCollector asCollector} instead, since those 4006 * arguments will not need to be live on the stack on entry to the 4007 * target.) 4008 * <p><b>Example:</b> 4009 * <blockquote><pre>{@code 4010 import static java.lang.invoke.MethodHandles.*; 4011 import static java.lang.invoke.MethodType.*; 4012 ... 4013 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 4014 "println", methodType(void.class, String.class)) 4015 .bindTo(System.out); 4016 MethodHandle cat = lookup().findVirtual(String.class, 4017 "concat", methodType(String.class, String.class)); 4018 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 4019 MethodHandle catTrace = foldArguments(cat, trace); 4020 // also prints "boo": 4021 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 4022 * }</pre></blockquote> 4023 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 4024 * represents the result type of the {@code target} and resulting adapter. 4025 * {@code V}/{@code v} represent the type and value of the parameter and argument 4026 * of {@code target} that precedes the folding position; {@code V} also is 4027 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 4028 * types and values of the {@code N} parameters and arguments at the folding 4029 * position. {@code B}/{@code b} represent the types and values of the 4030 * {@code target} parameters and arguments that follow the folded parameters 4031 * and arguments. 4032 * <blockquote><pre>{@code 4033 * // there are N arguments in A... 4034 * T target(V, A[N]..., B...); 4035 * V combiner(A...); 4036 * T adapter(A... a, B... b) { 4037 * V v = combiner(a...); 4038 * return target(v, a..., b...); 4039 * } 4040 * // and if the combiner has a void return: 4041 * T target2(A[N]..., B...); 4042 * void combiner2(A...); 4043 * T adapter2(A... a, B... b) { 4044 * combiner2(a...); 4045 * return target2(a..., b...); 4046 * } 4047 * }</pre></blockquote> 4048 * <p> 4049 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4050 * variable-arity method handle}, even if the original target method handle was. 4051 * @param target the method handle to invoke after arguments are combined 4052 * @param combiner method handle to call initially on the incoming arguments 4053 * @return method handle which incorporates the specified argument folding logic 4054 * @throws NullPointerException if either argument is null 4055 * @throws IllegalArgumentException if {@code combiner}'s return type 4056 * is non-void and not the same as the first argument type of 4057 * the target, or if the initial {@code N} argument types 4058 * of the target 4059 * (skipping one matching the {@code combiner}'s return type) 4060 * are not identical with the argument types of {@code combiner} 4061 */ 4062 public static foldArguments(MethodHandle target, MethodHandle combiner)4063 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) { 4064 return foldArguments(target, 0, combiner); 4065 } 4066 4067 /** 4068 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then 4069 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just 4070 * before the folded arguments. 4071 * <p> 4072 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the 4073 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a 4074 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position 4075 * 0. 4076 * 4077 * @apiNote Example: 4078 * <blockquote><pre>{@code 4079 import static java.lang.invoke.MethodHandles.*; 4080 import static java.lang.invoke.MethodType.*; 4081 ... 4082 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 4083 "println", methodType(void.class, String.class)) 4084 .bindTo(System.out); 4085 MethodHandle cat = lookup().findVirtual(String.class, 4086 "concat", methodType(String.class, String.class)); 4087 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 4088 MethodHandle catTrace = foldArguments(cat, 1, trace); 4089 // also prints "jum": 4090 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 4091 * }</pre></blockquote> 4092 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 4093 * represents the result type of the {@code target} and resulting adapter. 4094 * {@code V}/{@code v} represent the type and value of the parameter and argument 4095 * of {@code target} that precedes the folding position; {@code V} also is 4096 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 4097 * types and values of the {@code N} parameters and arguments at the folding 4098 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types 4099 * and values of the {@code target} parameters and arguments that precede and 4100 * follow the folded parameters and arguments starting at {@code pos}, 4101 * respectively. 4102 * <blockquote><pre>{@code 4103 * // there are N arguments in A... 4104 * T target(Z..., V, A[N]..., B...); 4105 * V combiner(A...); 4106 * T adapter(Z... z, A... a, B... b) { 4107 * V v = combiner(a...); 4108 * return target(z..., v, a..., b...); 4109 * } 4110 * // and if the combiner has a void return: 4111 * T target2(Z..., A[N]..., B...); 4112 * void combiner2(A...); 4113 * T adapter2(Z... z, A... a, B... b) { 4114 * combiner2(a...); 4115 * return target2(z..., a..., b...); 4116 * } 4117 * }</pre></blockquote> 4118 * <p> 4119 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4120 * variable-arity method handle}, even if the original target method handle was. 4121 * 4122 * @param target the method handle to invoke after arguments are combined 4123 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code 4124 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 4125 * @param combiner method handle to call initially on the incoming arguments 4126 * @return method handle which incorporates the specified argument folding logic 4127 * @throws NullPointerException if either argument is null 4128 * @throws IllegalArgumentException if either of the following two conditions holds: 4129 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 4130 * {@code pos} of the target signature; 4131 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching 4132 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}. 4133 * 4134 * @see #foldArguments(MethodHandle, MethodHandle) 4135 * @since 9 4136 */ 4137 public static foldArguments(MethodHandle target, int pos, MethodHandle combiner)4138 MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) { 4139 MethodType targetType = target.type(); 4140 MethodType combinerType = combiner.type(); 4141 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType); 4142 // Android-changed: // Android-changed: transformer implementation. 4143 // BoundMethodHandle result = target.rebind(); 4144 // boolean dropResult = rtype == void.class; 4145 // LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType()); 4146 // MethodType newType = targetType; 4147 // if (!dropResult) { 4148 // newType = newType.dropParameterTypes(pos, pos + 1); 4149 // } 4150 // result = result.copyWithExtendL(newType, lform, combiner); 4151 // return result; 4152 4153 return new Transformers.FoldArguments(target, pos, combiner); 4154 } 4155 foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType)4156 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) { 4157 int foldArgs = combinerType.parameterCount(); 4158 Class<?> rtype = combinerType.returnType(); 4159 int foldVals = rtype == void.class ? 0 : 1; 4160 int afterInsertPos = foldPos + foldVals; 4161 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs); 4162 if (ok) { 4163 for (int i = 0; i < foldArgs; i++) { 4164 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) { 4165 ok = false; 4166 break; 4167 } 4168 } 4169 } 4170 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) 4171 ok = false; 4172 if (!ok) 4173 throw misMatchedTypes("target and combiner types", targetType, combinerType); 4174 return rtype; 4175 } 4176 4177 /** 4178 * Makes a method handle which adapts a target method handle, 4179 * by guarding it with a test, a boolean-valued method handle. 4180 * If the guard fails, a fallback handle is called instead. 4181 * All three method handles must have the same corresponding 4182 * argument and return types, except that the return type 4183 * of the test must be boolean, and the test is allowed 4184 * to have fewer arguments than the other two method handles. 4185 * <p> Here is pseudocode for the resulting adapter: 4186 * <blockquote><pre>{@code 4187 * boolean test(A...); 4188 * T target(A...,B...); 4189 * T fallback(A...,B...); 4190 * T adapter(A... a,B... b) { 4191 * if (test(a...)) 4192 * return target(a..., b...); 4193 * else 4194 * return fallback(a..., b...); 4195 * } 4196 * }</pre></blockquote> 4197 * Note that the test arguments ({@code a...} in the pseudocode) cannot 4198 * be modified by execution of the test, and so are passed unchanged 4199 * from the caller to the target or fallback as appropriate. 4200 * @param test method handle used for test, must return boolean 4201 * @param target method handle to call if test passes 4202 * @param fallback method handle to call if test fails 4203 * @return method handle which incorporates the specified if/then/else logic 4204 * @throws NullPointerException if any argument is null 4205 * @throws IllegalArgumentException if {@code test} does not return boolean, 4206 * or if all three method types do not match (with the return 4207 * type of {@code test} changed to match that of the target). 4208 */ 4209 public static guardWithTest(MethodHandle test, MethodHandle target, MethodHandle fallback)4210 MethodHandle guardWithTest(MethodHandle test, 4211 MethodHandle target, 4212 MethodHandle fallback) { 4213 MethodType gtype = test.type(); 4214 MethodType ttype = target.type(); 4215 MethodType ftype = fallback.type(); 4216 if (!ttype.equals(ftype)) 4217 throw misMatchedTypes("target and fallback types", ttype, ftype); 4218 if (gtype.returnType() != boolean.class) 4219 throw newIllegalArgumentException("guard type is not a predicate "+gtype); 4220 List<Class<?>> targs = ttype.parameterList(); 4221 List<Class<?>> gargs = gtype.parameterList(); 4222 if (!targs.equals(gargs)) { 4223 int gpc = gargs.size(), tpc = targs.size(); 4224 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs)) 4225 throw misMatchedTypes("target and test types", ttype, gtype); 4226 test = dropArguments(test, gpc, targs.subList(gpc, tpc)); 4227 gtype = test.type(); 4228 } 4229 4230 return new Transformers.GuardWithTest(test, target, fallback); 4231 } 4232 misMatchedTypes(String what, T t1, T t2)4233 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) { 4234 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2); 4235 } 4236 4237 /** 4238 * Makes a method handle which adapts a target method handle, 4239 * by running it inside an exception handler. 4240 * If the target returns normally, the adapter returns that value. 4241 * If an exception matching the specified type is thrown, the fallback 4242 * handle is called instead on the exception, plus the original arguments. 4243 * <p> 4244 * The target and handler must have the same corresponding 4245 * argument and return types, except that handler may omit trailing arguments 4246 * (similarly to the predicate in {@link #guardWithTest guardWithTest}). 4247 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype. 4248 * <p> 4249 * Here is pseudocode for the resulting adapter. In the code, {@code T} 4250 * represents the return type of the {@code target} and {@code handler}, 4251 * and correspondingly that of the resulting adapter; {@code A}/{@code a}, 4252 * the types and values of arguments to the resulting handle consumed by 4253 * {@code handler}; and {@code B}/{@code b}, those of arguments to the 4254 * resulting handle discarded by {@code handler}. 4255 * <blockquote><pre>{@code 4256 * T target(A..., B...); 4257 * T handler(ExType, A...); 4258 * T adapter(A... a, B... b) { 4259 * try { 4260 * return target(a..., b...); 4261 * } catch (ExType ex) { 4262 * return handler(ex, a...); 4263 * } 4264 * } 4265 * }</pre></blockquote> 4266 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 4267 * be modified by execution of the target, and so are passed unchanged 4268 * from the caller to the handler, if the handler is invoked. 4269 * <p> 4270 * The target and handler must return the same type, even if the handler 4271 * always throws. (This might happen, for instance, because the handler 4272 * is simulating a {@code finally} clause). 4273 * To create such a throwing handler, compose the handler creation logic 4274 * with {@link #throwException throwException}, 4275 * in order to create a method handle of the correct return type. 4276 * @param target method handle to call 4277 * @param exType the type of exception which the handler will catch 4278 * @param handler method handle to call if a matching exception is thrown 4279 * @return method handle which incorporates the specified try/catch logic 4280 * @throws NullPointerException if any argument is null 4281 * @throws IllegalArgumentException if {@code handler} does not accept 4282 * the given exception type, or if the method handle types do 4283 * not match in their return types and their 4284 * corresponding parameters 4285 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle) 4286 */ 4287 public static catchException(MethodHandle target, Class<? extends Throwable> exType, MethodHandle handler)4288 MethodHandle catchException(MethodHandle target, 4289 Class<? extends Throwable> exType, 4290 MethodHandle handler) { 4291 MethodType ttype = target.type(); 4292 MethodType htype = handler.type(); 4293 if (!Throwable.class.isAssignableFrom(exType)) 4294 throw new ClassCastException(exType.getName()); 4295 if (htype.parameterCount() < 1 || 4296 !htype.parameterType(0).isAssignableFrom(exType)) 4297 throw newIllegalArgumentException("handler does not accept exception type "+exType); 4298 if (htype.returnType() != ttype.returnType()) 4299 throw misMatchedTypes("target and handler return types", ttype, htype); 4300 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true); 4301 if (handler == null) { 4302 throw misMatchedTypes("target and handler types", ttype, htype); 4303 } 4304 // Android-changed: use Transformer implementation. 4305 // return MethodHandleImpl.makeGuardWithCatch(target, exType, handler); 4306 return new Transformers.CatchException(target, handler, exType); 4307 } 4308 4309 /** 4310 * Produces a method handle which will throw exceptions of the given {@code exType}. 4311 * The method handle will accept a single argument of {@code exType}, 4312 * and immediately throw it as an exception. 4313 * The method type will nominally specify a return of {@code returnType}. 4314 * The return type may be anything convenient: It doesn't matter to the 4315 * method handle's behavior, since it will never return normally. 4316 * @param returnType the return type of the desired method handle 4317 * @param exType the parameter type of the desired method handle 4318 * @return method handle which can throw the given exceptions 4319 * @throws NullPointerException if either argument is null 4320 */ 4321 public static throwException(Class<?> returnType, Class<? extends Throwable> exType)4322 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) { 4323 if (!Throwable.class.isAssignableFrom(exType)) 4324 throw new ClassCastException(exType.getName()); 4325 // Android-changed: use Transformer implementation. 4326 // return MethodHandleImpl.throwException(methodType(returnType, exType)); 4327 return new Transformers.AlwaysThrow(returnType, exType); 4328 } 4329 4330 /** 4331 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each 4332 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and 4333 * delivers the loop's result, which is the return value of the resulting handle. 4334 * <p> 4335 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop 4336 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration 4337 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in 4338 * terms of method handles, each clause will specify up to four independent actions:<ul> 4339 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}. 4340 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}. 4341 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit. 4342 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value. 4343 * </ul> 4344 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}. 4345 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually 4346 * be referring to types, but in some contexts (describing execution) the lists will be of actual values. 4347 * <p> 4348 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in 4349 * this case. See below for a detailed description. 4350 * <p> 4351 * <em>Parameters optional everywhere:</em> 4352 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}. 4353 * As an exception, the init functions cannot take any {@code v} parameters, 4354 * because those values are not yet computed when the init functions are executed. 4355 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take. 4356 * In fact, any clause function may take no arguments at all. 4357 * <p> 4358 * <em>Loop parameters:</em> 4359 * A clause function may take all the iteration variable values it is entitled to, in which case 4360 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>, 4361 * with their types and values notated as {@code (A...)} and {@code (a...)}. 4362 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed. 4363 * (Since init functions do not accept iteration variables {@code v}, any parameter to an 4364 * init function is automatically a loop parameter {@code a}.) 4365 * As with iteration variables, clause functions are allowed but not required to accept loop parameters. 4366 * These loop parameters act as loop-invariant values visible across the whole loop. 4367 * <p> 4368 * <em>Parameters visible everywhere:</em> 4369 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full 4370 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters. 4371 * The init functions can observe initial pre-loop state, in the form {@code (a...)}. 4372 * Most clause functions will not need all of this information, but they will be formally connected to it 4373 * as if by {@link #dropArguments}. 4374 * <a id="astar"></a> 4375 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full 4376 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}). 4377 * In that notation, the general form of an init function parameter list 4378 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}. 4379 * <p> 4380 * <em>Checking clause structure:</em> 4381 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the 4382 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must" 4383 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not 4384 * met by the inputs to the loop combinator. 4385 * <p> 4386 * <em>Effectively identical sequences:</em> 4387 * <a id="effid"></a> 4388 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B} 4389 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}. 4390 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical" 4391 * as a whole if the set contains a longest list, and all members of the set are effectively identical to 4392 * that longest list. 4393 * For example, any set of type sequences of the form {@code (V*)} is effectively identical, 4394 * and the same is true if more sequences of the form {@code (V... A*)} are added. 4395 * <p> 4396 * <em>Step 0: Determine clause structure.</em><ol type="a"> 4397 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element. 4398 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements. 4399 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length 4400 * four. Padding takes place by appending elements to the array. 4401 * <li>Clauses with all {@code null}s are disregarded. 4402 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini". 4403 * </ol> 4404 * <p> 4405 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a"> 4406 * <li>The iteration variable type for each clause is determined using the clause's init and step return types. 4407 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is 4408 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's 4409 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's 4410 * iteration variable type. 4411 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}. 4412 * <li>This list of types is called the "iteration variable types" ({@code (V...)}). 4413 * </ol> 4414 * <p> 4415 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul> 4416 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}). 4417 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types. 4418 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.) 4419 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types. 4420 * (These types will be checked in step 2, along with all the clause function types.) 4421 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.) 4422 * <li>All of the collected parameter lists must be effectively identical. 4423 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}). 4424 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence. 4425 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called 4426 * the "internal parameter list". 4427 * </ul> 4428 * <p> 4429 * <em>Step 1C: Determine loop return type.</em><ol type="a"> 4430 * <li>Examine fini function return types, disregarding omitted fini functions. 4431 * <li>If there are no fini functions, the loop return type is {@code void}. 4432 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return 4433 * type. 4434 * </ol> 4435 * <p> 4436 * <em>Step 1D: Check other types.</em><ol type="a"> 4437 * <li>There must be at least one non-omitted pred function. 4438 * <li>Every non-omitted pred function must have a {@code boolean} return type. 4439 * </ol> 4440 * <p> 4441 * <em>Step 2: Determine parameter lists.</em><ol type="a"> 4442 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}. 4443 * <li>The parameter list for init functions will be adjusted to the external parameter list. 4444 * (Note that their parameter lists are already effectively identical to this list.) 4445 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be 4446 * effectively identical to the internal parameter list {@code (V... A...)}. 4447 * </ol> 4448 * <p> 4449 * <em>Step 3: Fill in omitted functions.</em><ol type="a"> 4450 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable 4451 * type. 4452 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration 4453 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void} 4454 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.) 4455 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far 4456 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.) 4457 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the 4458 * loop return type. 4459 * </ol> 4460 * <p> 4461 * <em>Step 4: Fill in missing parameter types.</em><ol type="a"> 4462 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)}, 4463 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list. 4464 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter 4465 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list, 4466 * pad out the end of the list. 4467 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}. 4468 * </ol> 4469 * <p> 4470 * <em>Final observations.</em><ol type="a"> 4471 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments. 4472 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have. 4473 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have. 4474 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of 4475 * (non-{@code void}) iteration variables {@code V} followed by loop parameters. 4476 * <li>Each pair of init and step functions agrees in their return type {@code V}. 4477 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables. 4478 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters. 4479 * </ol> 4480 * <p> 4481 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property: 4482 * <ul> 4483 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}. 4484 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters. 4485 * (Only one {@code Pn} has to be non-{@code null}.) 4486 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}. 4487 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types. 4488 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}. 4489 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}. 4490 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine 4491 * the resulting loop handle's parameter types {@code (A...)}. 4492 * </ul> 4493 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions, 4494 * which is natural if most of the loop computation happens in the steps. For some loops, 4495 * the burden of computation might be heaviest in the pred functions, and so the pred functions 4496 * might need to accept the loop parameter values. For loops with complex exit logic, the fini 4497 * functions might need to accept loop parameters, and likewise for loops with complex entry logic, 4498 * where the init functions will need the extra parameters. For such reasons, the rules for 4499 * determining these parameters are as symmetric as possible, across all clause parts. 4500 * In general, the loop parameters function as common invariant values across the whole 4501 * loop, while the iteration variables function as common variant values, or (if there is 4502 * no step function) as internal loop invariant temporaries. 4503 * <p> 4504 * <em>Loop execution.</em><ol type="a"> 4505 * <li>When the loop is called, the loop input values are saved in locals, to be passed to 4506 * every clause function. These locals are loop invariant. 4507 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)}) 4508 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals. 4509 * These locals will be loop varying (unless their steps behave as identity functions, as noted above). 4510 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of 4511 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)} 4512 * (in argument order). 4513 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function 4514 * returns {@code false}. 4515 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the 4516 * sequence {@code (v...)} of loop variables. 4517 * The updated value is immediately visible to all subsequent function calls. 4518 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value 4519 * (of type {@code R}) is returned from the loop as a whole. 4520 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit 4521 * except by throwing an exception. 4522 * </ol> 4523 * <p> 4524 * <em>Usage tips.</em> 4525 * <ul> 4526 * <li>Although each step function will receive the current values of <em>all</em> the loop variables, 4527 * sometimes a step function only needs to observe the current value of its own variable. 4528 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}. 4529 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}. 4530 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create 4531 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be 4532 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable. 4533 * <li>If some of the clause functions are virtual methods on an instance, the instance 4534 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause 4535 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference 4536 * will be the first iteration variable value, and it will be easy to use virtual 4537 * methods as clause parts, since all of them will take a leading instance reference matching that value. 4538 * </ul> 4539 * <p> 4540 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types 4541 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop; 4542 * and {@code R} is the common result type of all finalizers as well as of the resulting loop. 4543 * <blockquote><pre>{@code 4544 * V... init...(A...); 4545 * boolean pred...(V..., A...); 4546 * V... step...(V..., A...); 4547 * R fini...(V..., A...); 4548 * R loop(A... a) { 4549 * V... v... = init...(a...); 4550 * for (;;) { 4551 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) { 4552 * v = s(v..., a...); 4553 * if (!p(v..., a...)) { 4554 * return f(v..., a...); 4555 * } 4556 * } 4557 * } 4558 * } 4559 * }</pre></blockquote> 4560 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded 4561 * to their full length, even though individual clause functions may neglect to take them all. 4562 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}. 4563 * 4564 * @apiNote Example: 4565 * <blockquote><pre>{@code 4566 * // iterative implementation of the factorial function as a loop handle 4567 * static int one(int k) { return 1; } 4568 * static int inc(int i, int acc, int k) { return i + 1; } 4569 * static int mult(int i, int acc, int k) { return i * acc; } 4570 * static boolean pred(int i, int acc, int k) { return i < k; } 4571 * static int fin(int i, int acc, int k) { return acc; } 4572 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 4573 * // null initializer for counter, should initialize to 0 4574 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 4575 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 4576 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 4577 * assertEquals(120, loop.invoke(5)); 4578 * }</pre></blockquote> 4579 * The same example, dropping arguments and using combinators: 4580 * <blockquote><pre>{@code 4581 * // simplified implementation of the factorial function as a loop handle 4582 * static int inc(int i) { return i + 1; } // drop acc, k 4583 * static int mult(int i, int acc) { return i * acc; } //drop k 4584 * static boolean cmp(int i, int k) { return i < k; } 4585 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods 4586 * // null initializer for counter, should initialize to 0 4587 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 4588 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc 4589 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i 4590 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 4591 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 4592 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 4593 * assertEquals(720, loop.invoke(6)); 4594 * }</pre></blockquote> 4595 * A similar example, using a helper object to hold a loop parameter: 4596 * <blockquote><pre>{@code 4597 * // instance-based implementation of the factorial function as a loop handle 4598 * static class FacLoop { 4599 * final int k; 4600 * FacLoop(int k) { this.k = k; } 4601 * int inc(int i) { return i + 1; } 4602 * int mult(int i, int acc) { return i * acc; } 4603 * boolean pred(int i) { return i < k; } 4604 * int fin(int i, int acc) { return acc; } 4605 * } 4606 * // assume MH_FacLoop is a handle to the constructor 4607 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 4608 * // null initializer for counter, should initialize to 0 4609 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 4610 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop}; 4611 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 4612 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 4613 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause); 4614 * assertEquals(5040, loop.invoke(7)); 4615 * }</pre></blockquote> 4616 * 4617 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above. 4618 * 4619 * @return a method handle embodying the looping behavior as defined by the arguments. 4620 * 4621 * @throws IllegalArgumentException in case any of the constraints described above is violated. 4622 * 4623 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle) 4624 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 4625 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle) 4626 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle) 4627 * @since 9 4628 */ loop(MethodHandle[].... clauses)4629 public static MethodHandle loop(MethodHandle[]... clauses) { 4630 // Step 0: determine clause structure. 4631 loopChecks0(clauses); 4632 4633 List<MethodHandle> init = new ArrayList<>(); 4634 List<MethodHandle> step = new ArrayList<>(); 4635 List<MethodHandle> pred = new ArrayList<>(); 4636 List<MethodHandle> fini = new ArrayList<>(); 4637 4638 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> { 4639 init.add(clause[0]); // all clauses have at least length 1 4640 step.add(clause.length <= 1 ? null : clause[1]); 4641 pred.add(clause.length <= 2 ? null : clause[2]); 4642 fini.add(clause.length <= 3 ? null : clause[3]); 4643 }); 4644 4645 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1; 4646 final int nclauses = init.size(); 4647 4648 // Step 1A: determine iteration variables (V...). 4649 final List<Class<?>> iterationVariableTypes = new ArrayList<>(); 4650 for (int i = 0; i < nclauses; ++i) { 4651 MethodHandle in = init.get(i); 4652 MethodHandle st = step.get(i); 4653 if (in == null && st == null) { 4654 iterationVariableTypes.add(void.class); 4655 } else if (in != null && st != null) { 4656 loopChecks1a(i, in, st); 4657 iterationVariableTypes.add(in.type().returnType()); 4658 } else { 4659 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType()); 4660 } 4661 } 4662 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class). 4663 collect(Collectors.toList()); 4664 4665 // Step 1B: determine loop parameters (A...). 4666 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size()); 4667 loopChecks1b(init, commonSuffix); 4668 4669 // Step 1C: determine loop return type. 4670 // Step 1D: check other types. 4671 // local variable required here; see JDK-8223553 4672 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type) 4673 .map(MethodType::returnType); 4674 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class); 4675 loopChecks1cd(pred, fini, loopReturnType); 4676 4677 // Step 2: determine parameter lists. 4678 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix); 4679 commonParameterSequence.addAll(commonSuffix); 4680 loopChecks2(step, pred, fini, commonParameterSequence); 4681 4682 // Step 3: fill in omitted functions. 4683 for (int i = 0; i < nclauses; ++i) { 4684 Class<?> t = iterationVariableTypes.get(i); 4685 if (init.get(i) == null) { 4686 init.set(i, empty(methodType(t, commonSuffix))); 4687 } 4688 if (step.get(i) == null) { 4689 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i)); 4690 } 4691 if (pred.get(i) == null) { 4692 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence)); 4693 } 4694 if (fini.get(i) == null) { 4695 fini.set(i, empty(methodType(t, commonParameterSequence))); 4696 } 4697 } 4698 4699 // Step 4: fill in missing parameter types. 4700 // Also convert all handles to fixed-arity handles. 4701 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix)); 4702 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence)); 4703 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence)); 4704 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence)); 4705 4706 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList). 4707 allMatch(pl -> pl.equals(commonSuffix)); 4708 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList). 4709 allMatch(pl -> pl.equals(commonParameterSequence)); 4710 4711 // Android-changed: transformer implementation. 4712 // return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini); 4713 return new Transformers.Loop(loopReturnType, 4714 commonSuffix, 4715 finit.toArray(MethodHandle[]::new), 4716 fstep.toArray(MethodHandle[]::new), 4717 fpred.toArray(MethodHandle[]::new), 4718 ffini.toArray(MethodHandle[]::new)); 4719 } 4720 loopChecks0(MethodHandle[][] clauses)4721 private static void loopChecks0(MethodHandle[][] clauses) { 4722 if (clauses == null || clauses.length == 0) { 4723 throw newIllegalArgumentException("null or no clauses passed"); 4724 } 4725 if (Stream.of(clauses).anyMatch(Objects::isNull)) { 4726 throw newIllegalArgumentException("null clauses are not allowed"); 4727 } 4728 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) { 4729 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements."); 4730 } 4731 } 4732 loopChecks1a(int i, MethodHandle in, MethodHandle st)4733 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) { 4734 if (in.type().returnType() != st.type().returnType()) { 4735 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(), 4736 st.type().returnType()); 4737 } 4738 } 4739 longestParameterList(Stream<MethodHandle> mhs, int skipSize)4740 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) { 4741 final List<Class<?>> empty = List.of(); 4742 final List<Class<?>> longest = mhs.filter(Objects::nonNull). 4743 // take only those that can contribute to a common suffix because they are longer than the prefix 4744 map(MethodHandle::type). 4745 filter(t -> t.parameterCount() > skipSize). 4746 map(MethodType::parameterList). 4747 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty); 4748 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size()); 4749 } 4750 longestParameterList(List<List<Class<?>>> lists)4751 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) { 4752 final List<Class<?>> empty = List.of(); 4753 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty); 4754 } 4755 buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize)4756 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) { 4757 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize); 4758 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0); 4759 return longestParameterList(Arrays.asList(longest1, longest2)); 4760 } 4761 loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix)4762 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) { 4763 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type). 4764 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) { 4765 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init + 4766 " (common suffix: " + commonSuffix + ")"); 4767 } 4768 } 4769 loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType)4770 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) { 4771 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 4772 anyMatch(t -> t != loopReturnType)) { 4773 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " + 4774 loopReturnType + ")"); 4775 } 4776 4777 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) { 4778 throw newIllegalArgumentException("no predicate found", pred); 4779 } 4780 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 4781 anyMatch(t -> t != boolean.class)) { 4782 throw newIllegalArgumentException("predicates must have boolean return type", pred); 4783 } 4784 } 4785 loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence)4786 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) { 4787 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type). 4788 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) { 4789 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step + 4790 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")"); 4791 } 4792 } 4793 fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams)4794 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) { 4795 return hs.stream().map(h -> { 4796 int pc = h.type().parameterCount(); 4797 int tpsize = targetParams.size(); 4798 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h; 4799 }).collect(Collectors.toList()); 4800 } 4801 fixArities(List<MethodHandle> hs)4802 private static List<MethodHandle> fixArities(List<MethodHandle> hs) { 4803 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList()); 4804 } 4805 4806 /** 4807 * Constructs a {@code while} loop from an initializer, a body, and a predicate. 4808 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 4809 * <p> 4810 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 4811 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate 4812 * evaluates to {@code true}). 4813 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case). 4814 * <p> 4815 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 4816 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 4817 * and updated with the value returned from its invocation. The result of loop execution will be 4818 * the final value of the additional loop-local variable (if present). 4819 * <p> 4820 * The following rules hold for these argument handles:<ul> 4821 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 4822 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 4823 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 4824 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 4825 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 4826 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 4827 * It will constrain the parameter lists of the other loop parts. 4828 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 4829 * list {@code (A...)} is called the <em>external parameter list</em>. 4830 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 4831 * additional state variable of the loop. 4832 * The body must both accept and return a value of this type {@code V}. 4833 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 4834 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 4835 * <a href="MethodHandles.html#effid">effectively identical</a> 4836 * to the external parameter list {@code (A...)}. 4837 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 4838 * {@linkplain #empty default value}. 4839 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 4840 * Its parameter list (either empty or of the form {@code (V A*)}) must be 4841 * effectively identical to the internal parameter list. 4842 * </ul> 4843 * <p> 4844 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 4845 * <li>The loop handle's result type is the result type {@code V} of the body. 4846 * <li>The loop handle's parameter types are the types {@code (A...)}, 4847 * from the external parameter list. 4848 * </ul> 4849 * <p> 4850 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 4851 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 4852 * passed to the loop. 4853 * <blockquote><pre>{@code 4854 * V init(A...); 4855 * boolean pred(V, A...); 4856 * V body(V, A...); 4857 * V whileLoop(A... a...) { 4858 * V v = init(a...); 4859 * while (pred(v, a...)) { 4860 * v = body(v, a...); 4861 * } 4862 * return v; 4863 * } 4864 * }</pre></blockquote> 4865 * 4866 * @apiNote Example: 4867 * <blockquote><pre>{@code 4868 * // implement the zip function for lists as a loop handle 4869 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); } 4870 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); } 4871 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) { 4872 * zip.add(a.next()); 4873 * zip.add(b.next()); 4874 * return zip; 4875 * } 4876 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods 4877 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep); 4878 * List<String> a = Arrays.asList("a", "b", "c", "d"); 4879 * List<String> b = Arrays.asList("e", "f", "g", "h"); 4880 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h"); 4881 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator())); 4882 * }</pre></blockquote> 4883 * 4884 * 4885 * @apiNote The implementation of this method can be expressed as follows: 4886 * <blockquote><pre>{@code 4887 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 4888 * MethodHandle fini = (body.type().returnType() == void.class 4889 * ? null : identity(body.type().returnType())); 4890 * MethodHandle[] 4891 * checkExit = { null, null, pred, fini }, 4892 * varBody = { init, body }; 4893 * return loop(checkExit, varBody); 4894 * } 4895 * }</pre></blockquote> 4896 * 4897 * @param init optional initializer, providing the initial value of the loop variable. 4898 * May be {@code null}, implying a default initial value. See above for other constraints. 4899 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 4900 * above for other constraints. 4901 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 4902 * See above for other constraints. 4903 * 4904 * @return a method handle implementing the {@code while} loop as described by the arguments. 4905 * @throws IllegalArgumentException if the rules for the arguments are violated. 4906 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 4907 * 4908 * @see #loop(MethodHandle[][]) 4909 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 4910 * @since 9 4911 */ whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body)4912 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 4913 whileLoopChecks(init, pred, body); 4914 MethodHandle fini = identityOrVoid(body.type().returnType()); 4915 MethodHandle[] checkExit = { null, null, pred, fini }; 4916 MethodHandle[] varBody = { init, body }; 4917 return loop(checkExit, varBody); 4918 } 4919 4920 /** 4921 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. 4922 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 4923 * <p> 4924 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 4925 * method will, in each iteration, first execute its body and then evaluate the predicate. 4926 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body. 4927 * <p> 4928 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 4929 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 4930 * and updated with the value returned from its invocation. The result of loop execution will be 4931 * the final value of the additional loop-local variable (if present). 4932 * <p> 4933 * The following rules hold for these argument handles:<ul> 4934 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 4935 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 4936 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 4937 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 4938 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 4939 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 4940 * It will constrain the parameter lists of the other loop parts. 4941 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 4942 * list {@code (A...)} is called the <em>external parameter list</em>. 4943 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 4944 * additional state variable of the loop. 4945 * The body must both accept and return a value of this type {@code V}. 4946 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 4947 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 4948 * <a href="MethodHandles.html#effid">effectively identical</a> 4949 * to the external parameter list {@code (A...)}. 4950 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 4951 * {@linkplain #empty default value}. 4952 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 4953 * Its parameter list (either empty or of the form {@code (V A*)}) must be 4954 * effectively identical to the internal parameter list. 4955 * </ul> 4956 * <p> 4957 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 4958 * <li>The loop handle's result type is the result type {@code V} of the body. 4959 * <li>The loop handle's parameter types are the types {@code (A...)}, 4960 * from the external parameter list. 4961 * </ul> 4962 * <p> 4963 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 4964 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 4965 * passed to the loop. 4966 * <blockquote><pre>{@code 4967 * V init(A...); 4968 * boolean pred(V, A...); 4969 * V body(V, A...); 4970 * V doWhileLoop(A... a...) { 4971 * V v = init(a...); 4972 * do { 4973 * v = body(v, a...); 4974 * } while (pred(v, a...)); 4975 * return v; 4976 * } 4977 * }</pre></blockquote> 4978 * 4979 * @apiNote Example: 4980 * <blockquote><pre>{@code 4981 * // int i = 0; while (i < limit) { ++i; } return i; => limit 4982 * static int zero(int limit) { return 0; } 4983 * static int step(int i, int limit) { return i + 1; } 4984 * static boolean pred(int i, int limit) { return i < limit; } 4985 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods 4986 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred); 4987 * assertEquals(23, loop.invoke(23)); 4988 * }</pre></blockquote> 4989 * 4990 * 4991 * @apiNote The implementation of this method can be expressed as follows: 4992 * <blockquote><pre>{@code 4993 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 4994 * MethodHandle fini = (body.type().returnType() == void.class 4995 * ? null : identity(body.type().returnType())); 4996 * MethodHandle[] clause = { init, body, pred, fini }; 4997 * return loop(clause); 4998 * } 4999 * }</pre></blockquote> 5000 * 5001 * @param init optional initializer, providing the initial value of the loop variable. 5002 * May be {@code null}, implying a default initial value. See above for other constraints. 5003 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 5004 * See above for other constraints. 5005 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 5006 * above for other constraints. 5007 * 5008 * @return a method handle implementing the {@code while} loop as described by the arguments. 5009 * @throws IllegalArgumentException if the rules for the arguments are violated. 5010 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 5011 * 5012 * @see #loop(MethodHandle[][]) 5013 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle) 5014 * @since 9 5015 */ doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred)5016 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 5017 whileLoopChecks(init, pred, body); 5018 MethodHandle fini = identityOrVoid(body.type().returnType()); 5019 MethodHandle[] clause = {init, body, pred, fini }; 5020 return loop(clause); 5021 } 5022 whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body)5023 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) { 5024 Objects.requireNonNull(pred); 5025 Objects.requireNonNull(body); 5026 MethodType bodyType = body.type(); 5027 Class<?> returnType = bodyType.returnType(); 5028 List<Class<?>> innerList = bodyType.parameterList(); 5029 List<Class<?>> outerList = innerList; 5030 if (returnType == void.class) { 5031 // OK 5032 } else if (innerList.size() == 0 || innerList.get(0) != returnType) { 5033 // leading V argument missing => error 5034 MethodType expected = bodyType.insertParameterTypes(0, returnType); 5035 throw misMatchedTypes("body function", bodyType, expected); 5036 } else { 5037 outerList = innerList.subList(1, innerList.size()); 5038 } 5039 MethodType predType = pred.type(); 5040 if (predType.returnType() != boolean.class || 5041 !predType.effectivelyIdenticalParameters(0, innerList)) { 5042 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList)); 5043 } 5044 if (init != null) { 5045 MethodType initType = init.type(); 5046 if (initType.returnType() != returnType || 5047 !initType.effectivelyIdenticalParameters(0, outerList)) { 5048 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 5049 } 5050 } 5051 } 5052 5053 /** 5054 * Constructs a loop that runs a given number of iterations. 5055 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5056 * <p> 5057 * The number of iterations is determined by the {@code iterations} handle evaluation result. 5058 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}. 5059 * It will be initialized to 0 and incremented by 1 in each iteration. 5060 * <p> 5061 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 5062 * of that type is also present. This variable is initialized using the optional {@code init} handle, 5063 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 5064 * <p> 5065 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 5066 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 5067 * iteration variable. 5068 * The result of the loop handle execution will be the final {@code V} value of that variable 5069 * (or {@code void} if there is no {@code V} variable). 5070 * <p> 5071 * The following rules hold for the argument handles:<ul> 5072 * <li>The {@code iterations} handle must not be {@code null}, and must return 5073 * the type {@code int}, referred to here as {@code I} in parameter type lists. 5074 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5075 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 5076 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5077 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 5078 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 5079 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 5080 * of types called the <em>internal parameter list</em>. 5081 * It will constrain the parameter lists of the other loop parts. 5082 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 5083 * with no additional {@code A} types, then the internal parameter list is extended by 5084 * the argument types {@code A...} of the {@code iterations} handle. 5085 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 5086 * list {@code (A...)} is called the <em>external parameter list</em>. 5087 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5088 * additional state variable of the loop. 5089 * The body must both accept a leading parameter and return a value of this type {@code V}. 5090 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5091 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5092 * <a href="MethodHandles.html#effid">effectively identical</a> 5093 * to the external parameter list {@code (A...)}. 5094 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5095 * {@linkplain #empty default value}. 5096 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be 5097 * effectively identical to the external parameter list {@code (A...)}. 5098 * </ul> 5099 * <p> 5100 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5101 * <li>The loop handle's result type is the result type {@code V} of the body. 5102 * <li>The loop handle's parameter types are the types {@code (A...)}, 5103 * from the external parameter list. 5104 * </ul> 5105 * <p> 5106 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5107 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 5108 * arguments passed to the loop. 5109 * <blockquote><pre>{@code 5110 * int iterations(A...); 5111 * V init(A...); 5112 * V body(V, int, A...); 5113 * V countedLoop(A... a...) { 5114 * int end = iterations(a...); 5115 * V v = init(a...); 5116 * for (int i = 0; i < end; ++i) { 5117 * v = body(v, i, a...); 5118 * } 5119 * return v; 5120 * } 5121 * }</pre></blockquote> 5122 * 5123 * @apiNote Example with a fully conformant body method: 5124 * <blockquote><pre>{@code 5125 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 5126 * // => a variation on a well known theme 5127 * static String step(String v, int counter, String init) { return "na " + v; } 5128 * // assume MH_step is a handle to the method above 5129 * MethodHandle fit13 = MethodHandles.constant(int.class, 13); 5130 * MethodHandle start = MethodHandles.identity(String.class); 5131 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step); 5132 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!")); 5133 * }</pre></blockquote> 5134 * 5135 * @apiNote Example with the simplest possible body method type, 5136 * and passing the number of iterations to the loop invocation: 5137 * <blockquote><pre>{@code 5138 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 5139 * // => a variation on a well known theme 5140 * static String step(String v, int counter ) { return "na " + v; } 5141 * // assume MH_step is a handle to the method above 5142 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class); 5143 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class); 5144 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v 5145 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!")); 5146 * }</pre></blockquote> 5147 * 5148 * @apiNote Example that treats the number of iterations, string to append to, and string to append 5149 * as loop parameters: 5150 * <blockquote><pre>{@code 5151 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 5152 * // => a variation on a well known theme 5153 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; } 5154 * // assume MH_step is a handle to the method above 5155 * MethodHandle count = MethodHandles.identity(int.class); 5156 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class); 5157 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v 5158 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!")); 5159 * }</pre></blockquote> 5160 * 5161 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)} 5162 * to enforce a loop type: 5163 * <blockquote><pre>{@code 5164 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 5165 * // => a variation on a well known theme 5166 * static String step(String v, int counter, String pre) { return pre + " " + v; } 5167 * // assume MH_step is a handle to the method above 5168 * MethodType loopType = methodType(String.class, String.class, int.class, String.class); 5169 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1); 5170 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2); 5171 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0); 5172 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v 5173 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!")); 5174 * }</pre></blockquote> 5175 * 5176 * @apiNote The implementation of this method can be expressed as follows: 5177 * <blockquote><pre>{@code 5178 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 5179 * return countedLoop(empty(iterations.type()), iterations, init, body); 5180 * } 5181 * }</pre></blockquote> 5182 * 5183 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's 5184 * result type must be {@code int}. See above for other constraints. 5185 * @param init optional initializer, providing the initial value of the loop variable. 5186 * May be {@code null}, implying a default initial value. See above for other constraints. 5187 * @param body body of the loop, which may not be {@code null}. 5188 * It controls the loop parameters and result type in the standard case (see above for details). 5189 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 5190 * and may accept any number of additional types. 5191 * See above for other constraints. 5192 * 5193 * @return a method handle representing the loop. 5194 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}. 5195 * @throws IllegalArgumentException if any argument violates the rules formulated above. 5196 * 5197 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle) 5198 * @since 9 5199 */ countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body)5200 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 5201 return countedLoop(empty(iterations.type()), iterations, init, body); 5202 } 5203 5204 /** 5205 * Constructs a loop that counts over a range of numbers. 5206 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5207 * <p> 5208 * The loop counter {@code i} is a loop iteration variable of type {@code int}. 5209 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive) 5210 * values of the loop counter. 5211 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the 5212 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1. 5213 * <p> 5214 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 5215 * of that type is also present. This variable is initialized using the optional {@code init} handle, 5216 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 5217 * <p> 5218 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 5219 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 5220 * iteration variable. 5221 * The result of the loop handle execution will be the final {@code V} value of that variable 5222 * (or {@code void} if there is no {@code V} variable). 5223 * <p> 5224 * The following rules hold for the argument handles:<ul> 5225 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return 5226 * the common type {@code int}, referred to here as {@code I} in parameter type lists. 5227 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5228 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 5229 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5230 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 5231 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 5232 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 5233 * of types called the <em>internal parameter list</em>. 5234 * It will constrain the parameter lists of the other loop parts. 5235 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 5236 * with no additional {@code A} types, then the internal parameter list is extended by 5237 * the argument types {@code A...} of the {@code end} handle. 5238 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 5239 * list {@code (A...)} is called the <em>external parameter list</em>. 5240 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5241 * additional state variable of the loop. 5242 * The body must both accept a leading parameter and return a value of this type {@code V}. 5243 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5244 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5245 * <a href="MethodHandles.html#effid">effectively identical</a> 5246 * to the external parameter list {@code (A...)}. 5247 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5248 * {@linkplain #empty default value}. 5249 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be 5250 * effectively identical to the external parameter list {@code (A...)}. 5251 * <li>Likewise, the parameter list of {@code end} must be effectively identical 5252 * to the external parameter list. 5253 * </ul> 5254 * <p> 5255 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5256 * <li>The loop handle's result type is the result type {@code V} of the body. 5257 * <li>The loop handle's parameter types are the types {@code (A...)}, 5258 * from the external parameter list. 5259 * </ul> 5260 * <p> 5261 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5262 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 5263 * arguments passed to the loop. 5264 * <blockquote><pre>{@code 5265 * int start(A...); 5266 * int end(A...); 5267 * V init(A...); 5268 * V body(V, int, A...); 5269 * V countedLoop(A... a...) { 5270 * int e = end(a...); 5271 * int s = start(a...); 5272 * V v = init(a...); 5273 * for (int i = s; i < e; ++i) { 5274 * v = body(v, i, a...); 5275 * } 5276 * return v; 5277 * } 5278 * }</pre></blockquote> 5279 * 5280 * @apiNote The implementation of this method can be expressed as follows: 5281 * <blockquote><pre>{@code 5282 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 5283 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class); 5284 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with 5285 * // the following semantics: 5286 * // MH_increment: (int limit, int counter) -> counter + 1 5287 * // MH_predicate: (int limit, int counter) -> counter < limit 5288 * Class<?> counterType = start.type().returnType(); // int 5289 * Class<?> returnType = body.type().returnType(); 5290 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null; 5291 * if (returnType != void.class) { // ignore the V variable 5292 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 5293 * pred = dropArguments(pred, 1, returnType); // ditto 5294 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit 5295 * } 5296 * body = dropArguments(body, 0, counterType); // ignore the limit variable 5297 * MethodHandle[] 5298 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 5299 * bodyClause = { init, body }, // v = init(); v = body(v, i) 5300 * indexVar = { start, incr }; // i = start(); i = i + 1 5301 * return loop(loopLimit, bodyClause, indexVar); 5302 * } 5303 * }</pre></blockquote> 5304 * 5305 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}. 5306 * See above for other constraints. 5307 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to 5308 * {@code end-1}). The result type must be {@code int}. See above for other constraints. 5309 * @param init optional initializer, providing the initial value of the loop variable. 5310 * May be {@code null}, implying a default initial value. See above for other constraints. 5311 * @param body body of the loop, which may not be {@code null}. 5312 * It controls the loop parameters and result type in the standard case (see above for details). 5313 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 5314 * and may accept any number of additional types. 5315 * See above for other constraints. 5316 * 5317 * @return a method handle representing the loop. 5318 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}. 5319 * @throws IllegalArgumentException if any argument violates the rules formulated above. 5320 * 5321 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle) 5322 * @since 9 5323 */ countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body)5324 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 5325 countedLoopChecks(start, end, init, body); 5326 Class<?> counterType = start.type().returnType(); // int, but who's counting? 5327 Class<?> limitType = end.type().returnType(); // yes, int again 5328 Class<?> returnType = body.type().returnType(); 5329 // Android-changed: getConstantHandle is in MethodHandles. 5330 // MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep); 5331 // MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred); 5332 MethodHandle incr = getConstantHandle(MH_countedLoopStep); 5333 MethodHandle pred = getConstantHandle(MH_countedLoopPred); 5334 MethodHandle retv = null; 5335 if (returnType != void.class) { 5336 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 5337 pred = dropArguments(pred, 1, returnType); // ditto 5338 retv = dropArguments(identity(returnType), 0, counterType); 5339 } 5340 body = dropArguments(body, 0, counterType); // ignore the limit variable 5341 MethodHandle[] 5342 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 5343 bodyClause = { init, body }, // v = init(); v = body(v, i) 5344 indexVar = { start, incr }; // i = start(); i = i + 1 5345 return loop(loopLimit, bodyClause, indexVar); 5346 } 5347 countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body)5348 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 5349 Objects.requireNonNull(start); 5350 Objects.requireNonNull(end); 5351 Objects.requireNonNull(body); 5352 Class<?> counterType = start.type().returnType(); 5353 if (counterType != int.class) { 5354 MethodType expected = start.type().changeReturnType(int.class); 5355 throw misMatchedTypes("start function", start.type(), expected); 5356 } else if (end.type().returnType() != counterType) { 5357 MethodType expected = end.type().changeReturnType(counterType); 5358 throw misMatchedTypes("end function", end.type(), expected); 5359 } 5360 MethodType bodyType = body.type(); 5361 Class<?> returnType = bodyType.returnType(); 5362 List<Class<?>> innerList = bodyType.parameterList(); 5363 // strip leading V value if present 5364 int vsize = (returnType == void.class ? 0 : 1); 5365 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) { 5366 // argument list has no "V" => error 5367 MethodType expected = bodyType.insertParameterTypes(0, returnType); 5368 throw misMatchedTypes("body function", bodyType, expected); 5369 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) { 5370 // missing I type => error 5371 MethodType expected = bodyType.insertParameterTypes(vsize, counterType); 5372 throw misMatchedTypes("body function", bodyType, expected); 5373 } 5374 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size()); 5375 if (outerList.isEmpty()) { 5376 // special case; take lists from end handle 5377 outerList = end.type().parameterList(); 5378 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList(); 5379 } 5380 MethodType expected = methodType(counterType, outerList); 5381 if (!start.type().effectivelyIdenticalParameters(0, outerList)) { 5382 throw misMatchedTypes("start parameter types", start.type(), expected); 5383 } 5384 if (end.type() != start.type() && 5385 !end.type().effectivelyIdenticalParameters(0, outerList)) { 5386 throw misMatchedTypes("end parameter types", end.type(), expected); 5387 } 5388 if (init != null) { 5389 MethodType initType = init.type(); 5390 if (initType.returnType() != returnType || 5391 !initType.effectivelyIdenticalParameters(0, outerList)) { 5392 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 5393 } 5394 } 5395 } 5396 5397 /** 5398 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}. 5399 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5400 * <p> 5401 * The iterator itself will be determined by the evaluation of the {@code iterator} handle. 5402 * Each value it produces will be stored in a loop iteration variable of type {@code T}. 5403 * <p> 5404 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 5405 * of that type is also present. This variable is initialized using the optional {@code init} handle, 5406 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 5407 * <p> 5408 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 5409 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 5410 * iteration variable. 5411 * The result of the loop handle execution will be the final {@code V} value of that variable 5412 * (or {@code void} if there is no {@code V} variable). 5413 * <p> 5414 * The following rules hold for the argument handles:<ul> 5415 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5416 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}. 5417 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5418 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V} 5419 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.) 5420 * <li>The parameter list {@code (V T A...)} of the body contributes to a list 5421 * of types called the <em>internal parameter list</em>. 5422 * It will constrain the parameter lists of the other loop parts. 5423 * <li>As a special case, if the body contributes only {@code V} and {@code T} types, 5424 * with no additional {@code A} types, then the internal parameter list is extended by 5425 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the 5426 * single type {@code Iterable} is added and constitutes the {@code A...} list. 5427 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter 5428 * list {@code (A...)} is called the <em>external parameter list</em>. 5429 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5430 * additional state variable of the loop. 5431 * The body must both accept a leading parameter and return a value of this type {@code V}. 5432 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5433 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5434 * <a href="MethodHandles.html#effid">effectively identical</a> 5435 * to the external parameter list {@code (A...)}. 5436 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5437 * {@linkplain #empty default value}. 5438 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return 5439 * type {@code java.util.Iterator} or a subtype thereof. 5440 * The iterator it produces when the loop is executed will be assumed 5441 * to yield values which can be converted to type {@code T}. 5442 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be 5443 * effectively identical to the external parameter list {@code (A...)}. 5444 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves 5445 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list 5446 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator 5447 * handle parameter is adjusted to accept the leading {@code A} type, as if by 5448 * the {@link MethodHandle#asType asType} conversion method. 5449 * The leading {@code A} type must be {@code Iterable} or a subtype thereof. 5450 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}. 5451 * </ul> 5452 * <p> 5453 * The type {@code T} may be either a primitive or reference. 5454 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator}, 5455 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object} 5456 * as if by the {@link MethodHandle#asType asType} conversion method. 5457 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur 5458 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}. 5459 * <p> 5460 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5461 * <li>The loop handle's result type is the result type {@code V} of the body. 5462 * <li>The loop handle's parameter types are the types {@code (A...)}, 5463 * from the external parameter list. 5464 * </ul> 5465 * <p> 5466 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5467 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the 5468 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop. 5469 * <blockquote><pre>{@code 5470 * Iterator<T> iterator(A...); // defaults to Iterable::iterator 5471 * V init(A...); 5472 * V body(V,T,A...); 5473 * V iteratedLoop(A... a...) { 5474 * Iterator<T> it = iterator(a...); 5475 * V v = init(a...); 5476 * while (it.hasNext()) { 5477 * T t = it.next(); 5478 * v = body(v, t, a...); 5479 * } 5480 * return v; 5481 * } 5482 * }</pre></blockquote> 5483 * 5484 * @apiNote Example: 5485 * <blockquote><pre>{@code 5486 * // get an iterator from a list 5487 * static List<String> reverseStep(List<String> r, String e) { 5488 * r.add(0, e); 5489 * return r; 5490 * } 5491 * static List<String> newArrayList() { return new ArrayList<>(); } 5492 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods 5493 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep); 5494 * List<String> list = Arrays.asList("a", "b", "c", "d", "e"); 5495 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a"); 5496 * assertEquals(reversedList, (List<String>) loop.invoke(list)); 5497 * }</pre></blockquote> 5498 * 5499 * @apiNote The implementation of this method can be expressed approximately as follows: 5500 * <blockquote><pre>{@code 5501 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 5502 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable 5503 * Class<?> returnType = body.type().returnType(); 5504 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 5505 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype)); 5506 * MethodHandle retv = null, step = body, startIter = iterator; 5507 * if (returnType != void.class) { 5508 * // the simple thing first: in (I V A...), drop the I to get V 5509 * retv = dropArguments(identity(returnType), 0, Iterator.class); 5510 * // body type signature (V T A...), internal loop types (I V A...) 5511 * step = swapArguments(body, 0, 1); // swap V <-> T 5512 * } 5513 * if (startIter == null) startIter = MH_getIter; 5514 * MethodHandle[] 5515 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext()) 5516 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a) 5517 * return loop(iterVar, bodyClause); 5518 * } 5519 * }</pre></blockquote> 5520 * 5521 * @param iterator an optional handle to return the iterator to start the loop. 5522 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype. 5523 * See above for other constraints. 5524 * @param init optional initializer, providing the initial value of the loop variable. 5525 * May be {@code null}, implying a default initial value. See above for other constraints. 5526 * @param body body of the loop, which may not be {@code null}. 5527 * It controls the loop parameters and result type in the standard case (see above for details). 5528 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values), 5529 * and may accept any number of additional types. 5530 * See above for other constraints. 5531 * 5532 * @return a method handle embodying the iteration loop functionality. 5533 * @throws NullPointerException if the {@code body} handle is {@code null}. 5534 * @throws IllegalArgumentException if any argument violates the above requirements. 5535 * 5536 * @since 9 5537 */ iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body)5538 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 5539 Class<?> iterableType = iteratedLoopChecks(iterator, init, body); 5540 Class<?> returnType = body.type().returnType(); 5541 // Android-changed: getConstantHandle is in MethodHandles. 5542 // MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred); 5543 // MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext); 5544 MethodHandle hasNext = getConstantHandle(MH_iteratePred); 5545 MethodHandle nextRaw = getConstantHandle(MH_iterateNext); 5546 MethodHandle startIter; 5547 MethodHandle nextVal; 5548 { 5549 MethodType iteratorType; 5550 if (iterator == null) { 5551 // derive argument type from body, if available, else use Iterable 5552 // Android-changed: getConstantHandle is in MethodHandles. 5553 // startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator); 5554 startIter = getConstantHandle(MH_initIterator); 5555 iteratorType = startIter.type().changeParameterType(0, iterableType); 5556 } else { 5557 // force return type to the internal iterator class 5558 iteratorType = iterator.type().changeReturnType(Iterator.class); 5559 startIter = iterator; 5560 } 5561 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 5562 MethodType nextValType = nextRaw.type().changeReturnType(ttype); 5563 5564 // perform the asType transforms under an exception transformer, as per spec.: 5565 try { 5566 startIter = startIter.asType(iteratorType); 5567 nextVal = nextRaw.asType(nextValType); 5568 } catch (WrongMethodTypeException ex) { 5569 throw new IllegalArgumentException(ex); 5570 } 5571 } 5572 5573 MethodHandle retv = null, step = body; 5574 if (returnType != void.class) { 5575 // the simple thing first: in (I V A...), drop the I to get V 5576 retv = dropArguments(identity(returnType), 0, Iterator.class); 5577 // body type signature (V T A...), internal loop types (I V A...) 5578 step = swapArguments(body, 0, 1); // swap V <-> T 5579 } 5580 5581 MethodHandle[] 5582 iterVar = { startIter, null, hasNext, retv }, 5583 bodyClause = { init, filterArgument(step, 0, nextVal) }; 5584 return loop(iterVar, bodyClause); 5585 } 5586 iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body)5587 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) { 5588 Objects.requireNonNull(body); 5589 MethodType bodyType = body.type(); 5590 Class<?> returnType = bodyType.returnType(); 5591 List<Class<?>> internalParamList = bodyType.parameterList(); 5592 // strip leading V value if present 5593 int vsize = (returnType == void.class ? 0 : 1); 5594 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) { 5595 // argument list has no "V" => error 5596 MethodType expected = bodyType.insertParameterTypes(0, returnType); 5597 throw misMatchedTypes("body function", bodyType, expected); 5598 } else if (internalParamList.size() <= vsize) { 5599 // missing T type => error 5600 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class); 5601 throw misMatchedTypes("body function", bodyType, expected); 5602 } 5603 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size()); 5604 Class<?> iterableType = null; 5605 if (iterator != null) { 5606 // special case; if the body handle only declares V and T then 5607 // the external parameter list is obtained from iterator handle 5608 if (externalParamList.isEmpty()) { 5609 externalParamList = iterator.type().parameterList(); 5610 } 5611 MethodType itype = iterator.type(); 5612 if (!Iterator.class.isAssignableFrom(itype.returnType())) { 5613 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type"); 5614 } 5615 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) { 5616 MethodType expected = methodType(itype.returnType(), externalParamList); 5617 throw misMatchedTypes("iterator parameters", itype, expected); 5618 } 5619 } else { 5620 if (externalParamList.isEmpty()) { 5621 // special case; if the iterator handle is null and the body handle 5622 // only declares V and T then the external parameter list consists 5623 // of Iterable 5624 externalParamList = Arrays.asList(Iterable.class); 5625 iterableType = Iterable.class; 5626 } else { 5627 // special case; if the iterator handle is null and the external 5628 // parameter list is not empty then the first parameter must be 5629 // assignable to Iterable 5630 iterableType = externalParamList.get(0); 5631 if (!Iterable.class.isAssignableFrom(iterableType)) { 5632 throw newIllegalArgumentException( 5633 "inferred first loop argument must inherit from Iterable: " + iterableType); 5634 } 5635 } 5636 } 5637 if (init != null) { 5638 MethodType initType = init.type(); 5639 if (initType.returnType() != returnType || 5640 !initType.effectivelyIdenticalParameters(0, externalParamList)) { 5641 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList)); 5642 } 5643 } 5644 return iterableType; // help the caller a bit 5645 } 5646 swapArguments(MethodHandle mh, int i, int j)5647 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) { 5648 // there should be a better way to uncross my wires 5649 int arity = mh.type().parameterCount(); 5650 int[] order = new int[arity]; 5651 for (int k = 0; k < arity; k++) order[k] = k; 5652 order[i] = j; order[j] = i; 5653 Class<?>[] types = mh.type().parameterArray(); 5654 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti; 5655 MethodType swapType = methodType(mh.type().returnType(), types); 5656 return permuteArguments(mh, swapType, order); 5657 } 5658 5659 /** 5660 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block. 5661 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception 5662 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The 5663 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The 5664 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the 5665 * {@code try-finally} handle. 5666 * <p> 5667 * The {@code cleanup} handle will be passed one or two additional leading arguments. 5668 * The first is the exception thrown during the 5669 * execution of the {@code target} handle, or {@code null} if no exception was thrown. 5670 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception, 5671 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder. 5672 * The second argument is not present if the {@code target} handle has a {@code void} return type. 5673 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists 5674 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.) 5675 * <p> 5676 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except 5677 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or 5678 * two extra leading parameters:<ul> 5679 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and 5680 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry 5681 * the result from the execution of the {@code target} handle. 5682 * This parameter is not present if the {@code target} returns {@code void}. 5683 * </ul> 5684 * <p> 5685 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of 5686 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting 5687 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by 5688 * the cleanup. 5689 * <blockquote><pre>{@code 5690 * V target(A..., B...); 5691 * V cleanup(Throwable, V, A...); 5692 * V adapter(A... a, B... b) { 5693 * V result = (zero value for V); 5694 * Throwable throwable = null; 5695 * try { 5696 * result = target(a..., b...); 5697 * } catch (Throwable t) { 5698 * throwable = t; 5699 * throw t; 5700 * } finally { 5701 * result = cleanup(throwable, result, a...); 5702 * } 5703 * return result; 5704 * } 5705 * }</pre></blockquote> 5706 * <p> 5707 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 5708 * be modified by execution of the target, and so are passed unchanged 5709 * from the caller to the cleanup, if it is invoked. 5710 * <p> 5711 * The target and cleanup must return the same type, even if the cleanup 5712 * always throws. 5713 * To create such a throwing cleanup, compose the cleanup logic 5714 * with {@link #throwException throwException}, 5715 * in order to create a method handle of the correct return type. 5716 * <p> 5717 * Note that {@code tryFinally} never converts exceptions into normal returns. 5718 * In rare cases where exceptions must be converted in that way, first wrap 5719 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)} 5720 * to capture an outgoing exception, and then wrap with {@code tryFinally}. 5721 * <p> 5722 * It is recommended that the first parameter type of {@code cleanup} be 5723 * declared {@code Throwable} rather than a narrower subtype. This ensures 5724 * {@code cleanup} will always be invoked with whatever exception that 5725 * {@code target} throws. Declaring a narrower type may result in a 5726 * {@code ClassCastException} being thrown by the {@code try-finally} 5727 * handle if the type of the exception thrown by {@code target} is not 5728 * assignable to the first parameter type of {@code cleanup}. Note that 5729 * various exception types of {@code VirtualMachineError}, 5730 * {@code LinkageError}, and {@code RuntimeException} can in principle be 5731 * thrown by almost any kind of Java code, and a finally clause that 5732 * catches (say) only {@code IOException} would mask any of the others 5733 * behind a {@code ClassCastException}. 5734 * 5735 * @param target the handle whose execution is to be wrapped in a {@code try} block. 5736 * @param cleanup the handle that is invoked in the finally block. 5737 * 5738 * @return a method handle embodying the {@code try-finally} block composed of the two arguments. 5739 * @throws NullPointerException if any argument is null 5740 * @throws IllegalArgumentException if {@code cleanup} does not accept 5741 * the required leading arguments, or if the method handle types do 5742 * not match in their return types and their 5743 * corresponding trailing parameters 5744 * 5745 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle) 5746 * @since 9 5747 */ tryFinally(MethodHandle target, MethodHandle cleanup)5748 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) { 5749 List<Class<?>> targetParamTypes = target.type().parameterList(); 5750 Class<?> rtype = target.type().returnType(); 5751 5752 tryFinallyChecks(target, cleanup); 5753 5754 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments. 5755 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 5756 // target parameter list. 5757 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0); 5758 5759 // Ensure that the intrinsic type checks the instance thrown by the 5760 // target against the first parameter of cleanup 5761 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class)); 5762 5763 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case. 5764 // Android-changed: use Transformer implementation. 5765 // return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes); 5766 return new Transformers.TryFinally(target.asFixedArity(), cleanup.asFixedArity()); 5767 } 5768 tryFinallyChecks(MethodHandle target, MethodHandle cleanup)5769 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) { 5770 Class<?> rtype = target.type().returnType(); 5771 if (rtype != cleanup.type().returnType()) { 5772 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype); 5773 } 5774 MethodType cleanupType = cleanup.type(); 5775 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) { 5776 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class); 5777 } 5778 if (rtype != void.class && cleanupType.parameterType(1) != rtype) { 5779 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype); 5780 } 5781 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 5782 // target parameter list. 5783 int cleanupArgIndex = rtype == void.class ? 1 : 2; 5784 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) { 5785 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix", 5786 cleanup.type(), target.type()); 5787 } 5788 } 5789 5790 /** 5791 * Creates a table switch method handle, which can be used to switch over a set of target 5792 * method handles, based on a given target index, called selector. 5793 * <p> 5794 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)}, 5795 * and where {@code N} is the number of target method handles, the table switch method 5796 * handle will invoke the n-th target method handle from the list of target method handles. 5797 * <p> 5798 * For a selector value that does not fall in the range {@code [0, N)}, the table switch 5799 * method handle will invoke the given fallback method handle. 5800 * <p> 5801 * All method handles passed to this method must have the same type, with the additional 5802 * requirement that the leading parameter be of type {@code int}. The leading parameter 5803 * represents the selector. 5804 * <p> 5805 * Any trailing parameters present in the type will appear on the returned table switch 5806 * method handle as well. Any arguments assigned to these parameters will be forwarded, 5807 * together with the selector value, to the selected method handle when invoking it. 5808 * 5809 * @apiNote Example: 5810 * The cases each drop the {@code selector} value they are given, and take an additional 5811 * {@code String} argument, which is concatenated (using {@link String#concat(String)}) 5812 * to a specific constant label string for each case: 5813 * <blockquote><pre>{@code 5814 * MethodHandles.Lookup lookup = MethodHandles.lookup(); 5815 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat", 5816 * MethodType.methodType(String.class, String.class)); 5817 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class); 5818 * 5819 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: "); 5820 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: "); 5821 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: "); 5822 * 5823 * MethodHandle mhSwitch = MethodHandles.tableSwitch( 5824 * caseDefault, 5825 * case0, 5826 * case1 5827 * ); 5828 * 5829 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data")); 5830 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data")); 5831 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data")); 5832 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data")); 5833 * }</pre></blockquote> 5834 * 5835 * @param fallback the fallback method handle that is called when the selector is not 5836 * within the range {@code [0, N)}. 5837 * @param targets array of target method handles. 5838 * @return the table switch method handle. 5839 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any 5840 * any of the elements of the {@code targets} array are 5841 * {@code null}. 5842 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading 5843 * parameter of the fallback handle or any of the target 5844 * handles is not {@code int}, or if the types of 5845 * the fallback handle and all of target handles are 5846 * not the same. 5847 */ tableSwitch(MethodHandle fallback, MethodHandle... targets)5848 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) { 5849 Objects.requireNonNull(fallback); 5850 Objects.requireNonNull(targets); 5851 targets = targets.clone(); 5852 MethodType type = tableSwitchChecks(fallback, targets); 5853 // Android-changed: use a Transformer for the implementation. 5854 // return MethodHandleImpl.makeTableSwitch(type, fallback, targets); 5855 return new Transformers.TableSwitch(type, fallback, targets); 5856 } 5857 tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions)5858 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) { 5859 if (caseActions.length == 0) 5860 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions)); 5861 5862 MethodType expectedType = defaultCase.type(); 5863 5864 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class) 5865 throw new IllegalArgumentException( 5866 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions)); 5867 5868 for (MethodHandle mh : caseActions) { 5869 Objects.requireNonNull(mh); 5870 // Android-changed: MethodType's not interned. 5871 // if (mh.type() != expectedType) 5872 if (!mh.type().equals(expectedType)) 5873 throw new IllegalArgumentException( 5874 "Case actions must have the same type: " + Arrays.toString(caseActions)); 5875 } 5876 5877 return expectedType; 5878 } 5879 5880 // BEGIN Android-added: Code from OpenJDK's MethodHandleImpl. 5881 5882 /** 5883 * This method is bound as the predicate in {@linkplain MethodHandles#countedLoop(MethodHandle, MethodHandle, 5884 * MethodHandle) counting loops}. 5885 * 5886 * @param limit the upper bound of the parameter, statically bound at loop creation time. 5887 * @param counter the counter parameter, passed in during loop execution. 5888 * 5889 * @return whether the counter has reached the limit. 5890 * @hide 5891 */ countedLoopPredicate(int limit, int counter)5892 public static boolean countedLoopPredicate(int limit, int counter) { 5893 return counter < limit; 5894 } 5895 5896 /** 5897 * This method is bound as the step function in {@linkplain MethodHandles#countedLoop(MethodHandle, MethodHandle, 5898 * MethodHandle) counting loops} to increment the counter. 5899 * 5900 * @param limit the upper bound of the loop counter (ignored). 5901 * @param counter the loop counter. 5902 * 5903 * @return the loop counter incremented by 1. 5904 * @hide 5905 */ countedLoopStep(int limit, int counter)5906 public static int countedLoopStep(int limit, int counter) { 5907 return counter + 1; 5908 } 5909 5910 /** 5911 * This is bound to initialize the loop-local iterator in {@linkplain MethodHandles#iteratedLoop iterating loops}. 5912 * 5913 * @param it the {@link Iterable} over which the loop iterates. 5914 * 5915 * @return an {@link Iterator} over the argument's elements. 5916 * @hide 5917 */ initIterator(Iterable<?> it)5918 public static Iterator<?> initIterator(Iterable<?> it) { 5919 return it.iterator(); 5920 } 5921 5922 /** 5923 * This method is bound as the predicate in {@linkplain MethodHandles#iteratedLoop iterating loops}. 5924 * 5925 * @param it the iterator to be checked. 5926 * 5927 * @return {@code true} iff there are more elements to iterate over. 5928 * @hide 5929 */ iteratePredicate(Iterator<?> it)5930 public static boolean iteratePredicate(Iterator<?> it) { 5931 return it.hasNext(); 5932 } 5933 5934 /** 5935 * This method is bound as the step for retrieving the current value from the iterator in {@linkplain 5936 * MethodHandles#iteratedLoop iterating loops}. 5937 * 5938 * @param it the iterator. 5939 * 5940 * @return the next element from the iterator. 5941 * @hide 5942 */ iterateNext(Iterator<?> it)5943 public static Object iterateNext(Iterator<?> it) { 5944 return it.next(); 5945 } 5946 5947 // Indexes into constant method handles: 5948 static final int 5949 MH_cast = 0, 5950 MH_selectAlternative = 1, 5951 MH_copyAsPrimitiveArray = 2, 5952 MH_fillNewTypedArray = 3, 5953 MH_fillNewArray = 4, 5954 MH_arrayIdentity = 5, 5955 MH_countedLoopPred = 6, 5956 MH_countedLoopStep = 7, 5957 MH_initIterator = 8, 5958 MH_iteratePred = 9, 5959 MH_iterateNext = 10, 5960 MH_Array_newInstance = 11, 5961 MH_LIMIT = 12; 5962 getConstantHandle(int idx)5963 static MethodHandle getConstantHandle(int idx) { 5964 MethodHandle handle = HANDLES[idx]; 5965 if (handle != null) { 5966 return handle; 5967 } 5968 return setCachedHandle(idx, makeConstantHandle(idx)); 5969 } 5970 setCachedHandle(int idx, final MethodHandle method)5971 private static synchronized MethodHandle setCachedHandle(int idx, final MethodHandle method) { 5972 // Simulate a CAS, to avoid racy duplication of results. 5973 MethodHandle prev = HANDLES[idx]; 5974 if (prev != null) { 5975 return prev; 5976 } 5977 HANDLES[idx] = method; 5978 return method; 5979 } 5980 5981 // Local constant method handles: 5982 private static final @Stable MethodHandle[] HANDLES = new MethodHandle[MH_LIMIT]; 5983 makeConstantHandle(int idx)5984 private static MethodHandle makeConstantHandle(int idx) { 5985 try { 5986 // Android-added: local IMPL_LOOKUP. 5987 final Lookup IMPL_LOOKUP = MethodHandles.Lookup.IMPL_LOOKUP; 5988 switch (idx) { 5989 // Android-removed: not-used. 5990 /* 5991 case MH_cast: 5992 return IMPL_LOOKUP.findVirtual(Class.class, "cast", 5993 MethodType.methodType(Object.class, Object.class)); 5994 case MH_copyAsPrimitiveArray: 5995 return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "copyAsPrimitiveArray", 5996 MethodType.methodType(Object.class, Wrapper.class, Object[].class)); 5997 case MH_arrayIdentity: 5998 return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "identity", 5999 MethodType.methodType(Object[].class, Object[].class)); 6000 case MH_fillNewArray: 6001 return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "fillNewArray", 6002 MethodType.methodType(Object[].class, Integer.class, Object[].class)); 6003 case MH_fillNewTypedArray: 6004 return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "fillNewTypedArray", 6005 MethodType.methodType(Object[].class, Object[].class, Integer.class, Object[].class)); 6006 case MH_selectAlternative: 6007 return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "selectAlternative", 6008 MethodType.methodType(MethodHandle.class, boolean.class, MethodHandle.class, MethodHandle.class)); 6009 */ 6010 case MH_countedLoopPred: 6011 // Android-changed: methods moved to this file. 6012 // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "countedLoopPredicate", 6013 // MethodType.methodType(boolean.class, int.class, int.class)); 6014 return IMPL_LOOKUP.findStatic(MethodHandles.class, "countedLoopPredicate", 6015 MethodType.methodType(boolean.class, int.class, int.class)); 6016 case MH_countedLoopStep: 6017 // Android-changed: methods moved to this file. 6018 // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "countedLoopStep", 6019 // MethodType.methodType(int.class, int.class, int.class)); 6020 return IMPL_LOOKUP.findStatic(MethodHandles.class, "countedLoopStep", 6021 MethodType.methodType(int.class, int.class, int.class)); 6022 case MH_initIterator: 6023 // Android-changed: methods moved to this file. 6024 // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "initIterator", 6025 // MethodType.methodType(Iterator.class, Iterable.class)); 6026 return IMPL_LOOKUP.findStatic(MethodHandles.class, "initIterator", 6027 MethodType.methodType(Iterator.class, Iterable.class)); 6028 case MH_iteratePred: 6029 // Android-changed: methods moved to this file. 6030 // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "iteratePredicate", 6031 // MethodType.methodType(boolean.class, Iterator.class)); 6032 return IMPL_LOOKUP.findStatic(MethodHandles.class, "iteratePredicate", 6033 MethodType.methodType(boolean.class, Iterator.class)); 6034 case MH_iterateNext: 6035 // Android-changed: methods moved to this file. 6036 // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "iterateNext", 6037 // MethodType.methodType(Object.class, Iterator.class)); 6038 return IMPL_LOOKUP.findStatic(MethodHandles.class, "iterateNext", 6039 MethodType.methodType(Object.class, Iterator.class)); 6040 // Android-removed: not-used. 6041 /* 6042 case MH_Array_newInstance: 6043 return IMPL_LOOKUP.findStatic(Array.class, "newInstance", 6044 MethodType.methodType(Object.class, Class.class, int.class)); 6045 */ 6046 } 6047 } catch (ReflectiveOperationException ex) { 6048 throw newInternalError(ex); 6049 } 6050 6051 throw newInternalError("Unknown function index: " + idx); 6052 } 6053 // END Android-added: Code from OpenJDK's MethodHandleImpl. 6054 } 6055