1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. Oracle designates this 9 * particular file as subject to the "Classpath" exception as provided 10 * by Oracle in the LICENSE file that accompanied this code. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 23 * or visit www.oracle.com if you need additional information or have any 24 * questions. 25 */ 26 27 package java.util; 28 import java.lang.ref.WeakReference; 29 import java.lang.ref.ReferenceQueue; 30 import java.util.function.BiConsumer; 31 import java.util.function.BiFunction; 32 import java.util.function.Consumer; 33 34 35 /** 36 * Hash table based implementation of the <tt>Map</tt> interface, with 37 * <em>weak keys</em>. 38 * An entry in a <tt>WeakHashMap</tt> will automatically be removed when 39 * its key is no longer in ordinary use. More precisely, the presence of a 40 * mapping for a given key will not prevent the key from being discarded by the 41 * garbage collector, that is, made finalizable, finalized, and then reclaimed. 42 * When a key has been discarded its entry is effectively removed from the map, 43 * so this class behaves somewhat differently from other <tt>Map</tt> 44 * implementations. 45 * 46 * <p> Both null values and the null key are supported. This class has 47 * performance characteristics similar to those of the <tt>HashMap</tt> 48 * class, and has the same efficiency parameters of <em>initial capacity</em> 49 * and <em>load factor</em>. 50 * 51 * <p> Like most collection classes, this class is not synchronized. 52 * A synchronized <tt>WeakHashMap</tt> may be constructed using the 53 * {@link Collections#synchronizedMap Collections.synchronizedMap} 54 * method. 55 * 56 * <p> This class is intended primarily for use with key objects whose 57 * <tt>equals</tt> methods test for object identity using the 58 * <tt>==</tt> operator. Once such a key is discarded it can never be 59 * recreated, so it is impossible to do a lookup of that key in a 60 * <tt>WeakHashMap</tt> at some later time and be surprised that its entry 61 * has been removed. This class will work perfectly well with key objects 62 * whose <tt>equals</tt> methods are not based upon object identity, such 63 * as <tt>String</tt> instances. With such recreatable key objects, 64 * however, the automatic removal of <tt>WeakHashMap</tt> entries whose 65 * keys have been discarded may prove to be confusing. 66 * 67 * <p> The behavior of the <tt>WeakHashMap</tt> class depends in part upon 68 * the actions of the garbage collector, so several familiar (though not 69 * required) <tt>Map</tt> invariants do not hold for this class. Because 70 * the garbage collector may discard keys at any time, a 71 * <tt>WeakHashMap</tt> may behave as though an unknown thread is silently 72 * removing entries. In particular, even if you synchronize on a 73 * <tt>WeakHashMap</tt> instance and invoke none of its mutator methods, it 74 * is possible for the <tt>size</tt> method to return smaller values over 75 * time, for the <tt>isEmpty</tt> method to return <tt>false</tt> and 76 * then <tt>true</tt>, for the <tt>containsKey</tt> method to return 77 * <tt>true</tt> and later <tt>false</tt> for a given key, for the 78 * <tt>get</tt> method to return a value for a given key but later return 79 * <tt>null</tt>, for the <tt>put</tt> method to return 80 * <tt>null</tt> and the <tt>remove</tt> method to return 81 * <tt>false</tt> for a key that previously appeared to be in the map, and 82 * for successive examinations of the key set, the value collection, and 83 * the entry set to yield successively smaller numbers of elements. 84 * 85 * <p> Each key object in a <tt>WeakHashMap</tt> is stored indirectly as 86 * the referent of a weak reference. Therefore a key will automatically be 87 * removed only after the weak references to it, both inside and outside of the 88 * map, have been cleared by the garbage collector. 89 * 90 * <p> <strong>Implementation note:</strong> The value objects in a 91 * <tt>WeakHashMap</tt> are held by ordinary strong references. Thus care 92 * should be taken to ensure that value objects do not strongly refer to their 93 * own keys, either directly or indirectly, since that will prevent the keys 94 * from being discarded. Note that a value object may refer indirectly to its 95 * key via the <tt>WeakHashMap</tt> itself; that is, a value object may 96 * strongly refer to some other key object whose associated value object, in 97 * turn, strongly refers to the key of the first value object. If the values 98 * in the map do not rely on the map holding strong references to them, one way 99 * to deal with this is to wrap values themselves within 100 * <tt>WeakReferences</tt> before 101 * inserting, as in: <tt>m.put(key, new WeakReference(value))</tt>, 102 * and then unwrapping upon each <tt>get</tt>. 103 * 104 * <p>The iterators returned by the <tt>iterator</tt> method of the collections 105 * returned by all of this class's "collection view methods" are 106 * <i>fail-fast</i>: if the map is structurally modified at any time after the 107 * iterator is created, in any way except through the iterator's own 108 * <tt>remove</tt> method, the iterator will throw a {@link 109 * ConcurrentModificationException}. Thus, in the face of concurrent 110 * modification, the iterator fails quickly and cleanly, rather than risking 111 * arbitrary, non-deterministic behavior at an undetermined time in the future. 112 * 113 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 114 * as it is, generally speaking, impossible to make any hard guarantees in the 115 * presence of unsynchronized concurrent modification. Fail-fast iterators 116 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 117 * Therefore, it would be wrong to write a program that depended on this 118 * exception for its correctness: <i>the fail-fast behavior of iterators 119 * should be used only to detect bugs.</i> 120 * 121 * <p>This class is a member of the 122 * <a href="{@docRoot}openjdk-redirect.html?v=8&path=/technotes/guides/collections/index.html"> 123 * Java Collections Framework</a>. 124 * 125 * @param <K> the type of keys maintained by this map 126 * @param <V> the type of mapped values 127 * 128 * @author Doug Lea 129 * @author Josh Bloch 130 * @author Mark Reinhold 131 * @since 1.2 132 * @see java.util.HashMap 133 * @see java.lang.ref.WeakReference 134 */ 135 public class WeakHashMap<K,V> 136 extends AbstractMap<K,V> 137 implements Map<K,V> { 138 139 /** 140 * The default initial capacity -- MUST be a power of two. 141 */ 142 private static final int DEFAULT_INITIAL_CAPACITY = 16; 143 144 /** 145 * The maximum capacity, used if a higher value is implicitly specified 146 * by either of the constructors with arguments. 147 * MUST be a power of two <= 1<<30. 148 */ 149 private static final int MAXIMUM_CAPACITY = 1 << 30; 150 151 /** 152 * The load factor used when none specified in constructor. 153 */ 154 private static final float DEFAULT_LOAD_FACTOR = 0.75f; 155 156 /** 157 * The table, resized as necessary. Length MUST Always be a power of two. 158 */ 159 Entry<K,V>[] table; 160 161 /** 162 * The number of key-value mappings contained in this weak hash map. 163 */ 164 private int size; 165 166 /** 167 * The next size value at which to resize (capacity * load factor). 168 */ 169 private int threshold; 170 171 /** 172 * The load factor for the hash table. 173 */ 174 private final float loadFactor; 175 176 /** 177 * Reference queue for cleared WeakEntries 178 */ 179 private final ReferenceQueue<Object> queue = new ReferenceQueue<>(); 180 181 /** 182 * The number of times this WeakHashMap has been structurally modified. 183 * Structural modifications are those that change the number of 184 * mappings in the map or otherwise modify its internal structure 185 * (e.g., rehash). This field is used to make iterators on 186 * Collection-views of the map fail-fast. 187 * 188 * @see ConcurrentModificationException 189 */ 190 int modCount; 191 192 @SuppressWarnings("unchecked") newTable(int n)193 private Entry<K,V>[] newTable(int n) { 194 return (Entry<K,V>[]) new Entry[n]; 195 } 196 197 /** 198 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial 199 * capacity and the given load factor. 200 * 201 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt> 202 * @param loadFactor The load factor of the <tt>WeakHashMap</tt> 203 * @throws IllegalArgumentException if the initial capacity is negative, 204 * or if the load factor is nonpositive. 205 */ WeakHashMap(int initialCapacity, float loadFactor)206 public WeakHashMap(int initialCapacity, float loadFactor) { 207 if (initialCapacity < 0) 208 throw new IllegalArgumentException("Illegal Initial Capacity: "+ 209 initialCapacity); 210 if (initialCapacity > MAXIMUM_CAPACITY) 211 initialCapacity = MAXIMUM_CAPACITY; 212 213 if (loadFactor <= 0 || Float.isNaN(loadFactor)) 214 throw new IllegalArgumentException("Illegal Load factor: "+ 215 loadFactor); 216 int capacity = 1; 217 while (capacity < initialCapacity) 218 capacity <<= 1; 219 table = newTable(capacity); 220 this.loadFactor = loadFactor; 221 threshold = (int)(capacity * loadFactor); 222 } 223 224 /** 225 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial 226 * capacity and the default load factor (0.75). 227 * 228 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt> 229 * @throws IllegalArgumentException if the initial capacity is negative 230 */ WeakHashMap(int initialCapacity)231 public WeakHashMap(int initialCapacity) { 232 this(initialCapacity, DEFAULT_LOAD_FACTOR); 233 } 234 235 /** 236 * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial 237 * capacity (16) and load factor (0.75). 238 */ WeakHashMap()239 public WeakHashMap() { 240 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); 241 } 242 243 /** 244 * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the 245 * specified map. The <tt>WeakHashMap</tt> is created with the default 246 * load factor (0.75) and an initial capacity sufficient to hold the 247 * mappings in the specified map. 248 * 249 * @param m the map whose mappings are to be placed in this map 250 * @throws NullPointerException if the specified map is null 251 * @since 1.3 252 */ WeakHashMap(Map<? extends K, ? extends V> m)253 public WeakHashMap(Map<? extends K, ? extends V> m) { 254 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, 255 DEFAULT_INITIAL_CAPACITY), 256 DEFAULT_LOAD_FACTOR); 257 putAll(m); 258 } 259 260 // internal utilities 261 262 /** 263 * Value representing null keys inside tables. 264 */ 265 private static final Object NULL_KEY = new Object(); 266 267 /** 268 * Use NULL_KEY for key if it is null. 269 */ maskNull(Object key)270 private static Object maskNull(Object key) { 271 return (key == null) ? NULL_KEY : key; 272 } 273 274 /** 275 * Returns internal representation of null key back to caller as null. 276 */ unmaskNull(Object key)277 static Object unmaskNull(Object key) { 278 return (key == NULL_KEY) ? null : key; 279 } 280 281 /** 282 * Checks for equality of non-null reference x and possibly-null y. By 283 * default uses Object.equals. 284 */ eq(Object x, Object y)285 private static boolean eq(Object x, Object y) { 286 return x == y || x.equals(y); 287 } 288 289 /** 290 * Returns index for hash code h. 291 */ indexFor(int h, int length)292 private static int indexFor(int h, int length) { 293 return h & (length-1); 294 } 295 296 /** 297 * Expunges stale entries from the table. 298 */ expungeStaleEntries()299 private void expungeStaleEntries() { 300 for (Object x; (x = queue.poll()) != null; ) { 301 synchronized (queue) { 302 @SuppressWarnings("unchecked") 303 Entry<K,V> e = (Entry<K,V>) x; 304 int i = indexFor(e.hash, table.length); 305 306 Entry<K,V> prev = table[i]; 307 Entry<K,V> p = prev; 308 while (p != null) { 309 Entry<K,V> next = p.next; 310 if (p == e) { 311 if (prev == e) 312 table[i] = next; 313 else 314 prev.next = next; 315 // Must not null out e.next; 316 // stale entries may be in use by a HashIterator 317 e.value = null; // Help GC 318 size--; 319 break; 320 } 321 prev = p; 322 p = next; 323 } 324 } 325 } 326 } 327 328 /** 329 * Returns the table after first expunging stale entries. 330 */ getTable()331 private Entry<K,V>[] getTable() { 332 expungeStaleEntries(); 333 return table; 334 } 335 336 /** 337 * Returns the number of key-value mappings in this map. 338 * This result is a snapshot, and may not reflect unprocessed 339 * entries that will be removed before next attempted access 340 * because they are no longer referenced. 341 */ size()342 public int size() { 343 if (size == 0) 344 return 0; 345 expungeStaleEntries(); 346 return size; 347 } 348 349 /** 350 * Returns <tt>true</tt> if this map contains no key-value mappings. 351 * This result is a snapshot, and may not reflect unprocessed 352 * entries that will be removed before next attempted access 353 * because they are no longer referenced. 354 */ isEmpty()355 public boolean isEmpty() { 356 return size() == 0; 357 } 358 359 /** 360 * Returns the value to which the specified key is mapped, 361 * or {@code null} if this map contains no mapping for the key. 362 * 363 * <p>More formally, if this map contains a mapping from a key 364 * {@code k} to a value {@code v} such that {@code (key==null ? k==null : 365 * key.equals(k))}, then this method returns {@code v}; otherwise 366 * it returns {@code null}. (There can be at most one such mapping.) 367 * 368 * <p>A return value of {@code null} does not <i>necessarily</i> 369 * indicate that the map contains no mapping for the key; it's also 370 * possible that the map explicitly maps the key to {@code null}. 371 * The {@link #containsKey containsKey} operation may be used to 372 * distinguish these two cases. 373 * 374 * @see #put(Object, Object) 375 */ get(Object key)376 public V get(Object key) { 377 Object k = maskNull(key); 378 int h = sun.misc.Hashing.singleWordWangJenkinsHash(k); 379 Entry<K,V>[] tab = getTable(); 380 int index = indexFor(h, tab.length); 381 Entry<K,V> e = tab[index]; 382 while (e != null) { 383 if (e.hash == h && eq(k, e.get())) 384 return e.value; 385 e = e.next; 386 } 387 return null; 388 } 389 390 /** 391 * Returns <tt>true</tt> if this map contains a mapping for the 392 * specified key. 393 * 394 * @param key The key whose presence in this map is to be tested 395 * @return <tt>true</tt> if there is a mapping for <tt>key</tt>; 396 * <tt>false</tt> otherwise 397 */ containsKey(Object key)398 public boolean containsKey(Object key) { 399 return getEntry(key) != null; 400 } 401 402 /** 403 * Returns the entry associated with the specified key in this map. 404 * Returns null if the map contains no mapping for this key. 405 */ getEntry(Object key)406 Entry<K,V> getEntry(Object key) { 407 Object k = maskNull(key); 408 int h = sun.misc.Hashing.singleWordWangJenkinsHash(k); 409 Entry<K,V>[] tab = getTable(); 410 int index = indexFor(h, tab.length); 411 Entry<K,V> e = tab[index]; 412 while (e != null && !(e.hash == h && eq(k, e.get()))) 413 e = e.next; 414 return e; 415 } 416 417 /** 418 * Associates the specified value with the specified key in this map. 419 * If the map previously contained a mapping for this key, the old 420 * value is replaced. 421 * 422 * @param key key with which the specified value is to be associated. 423 * @param value value to be associated with the specified key. 424 * @return the previous value associated with <tt>key</tt>, or 425 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 426 * (A <tt>null</tt> return can also indicate that the map 427 * previously associated <tt>null</tt> with <tt>key</tt>.) 428 */ put(K key, V value)429 public V put(K key, V value) { 430 Object k = maskNull(key); 431 int h = sun.misc.Hashing.singleWordWangJenkinsHash(k); 432 Entry<K,V>[] tab = getTable(); 433 int i = indexFor(h, tab.length); 434 435 for (Entry<K,V> e = tab[i]; e != null; e = e.next) { 436 if (h == e.hash && eq(k, e.get())) { 437 V oldValue = e.value; 438 if (value != oldValue) 439 e.value = value; 440 return oldValue; 441 } 442 } 443 444 modCount++; 445 Entry<K,V> e = tab[i]; 446 tab[i] = new Entry<>(k, value, queue, h, e); 447 if (++size >= threshold) 448 resize(tab.length * 2); 449 return null; 450 } 451 452 /** 453 * Rehashes the contents of this map into a new array with a 454 * larger capacity. This method is called automatically when the 455 * number of keys in this map reaches its threshold. 456 * 457 * If current capacity is MAXIMUM_CAPACITY, this method does not 458 * resize the map, but sets threshold to Integer.MAX_VALUE. 459 * This has the effect of preventing future calls. 460 * 461 * @param newCapacity the new capacity, MUST be a power of two; 462 * must be greater than current capacity unless current 463 * capacity is MAXIMUM_CAPACITY (in which case value 464 * is irrelevant). 465 */ resize(int newCapacity)466 void resize(int newCapacity) { 467 Entry<K,V>[] oldTable = getTable(); 468 int oldCapacity = oldTable.length; 469 if (oldCapacity == MAXIMUM_CAPACITY) { 470 threshold = Integer.MAX_VALUE; 471 return; 472 } 473 474 Entry<K,V>[] newTable = newTable(newCapacity); 475 transfer(oldTable, newTable); 476 table = newTable; 477 478 /* 479 * If ignoring null elements and processing ref queue caused massive 480 * shrinkage, then restore old table. This should be rare, but avoids 481 * unbounded expansion of garbage-filled tables. 482 */ 483 if (size >= threshold / 2) { 484 threshold = (int)(newCapacity * loadFactor); 485 } else { 486 expungeStaleEntries(); 487 transfer(newTable, oldTable); 488 table = oldTable; 489 } 490 } 491 492 /** Transfers all entries from src to dest tables */ transfer(Entry<K,V>[] src, Entry<K,V>[] dest)493 private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) { 494 for (int j = 0; j < src.length; ++j) { 495 Entry<K,V> e = src[j]; 496 src[j] = null; 497 while (e != null) { 498 Entry<K,V> next = e.next; 499 Object key = e.get(); 500 if (key == null) { 501 e.next = null; // Help GC 502 e.value = null; // " " 503 size--; 504 } else { 505 int i = indexFor(e.hash, dest.length); 506 e.next = dest[i]; 507 dest[i] = e; 508 } 509 e = next; 510 } 511 } 512 } 513 514 /** 515 * Copies all of the mappings from the specified map to this map. 516 * These mappings will replace any mappings that this map had for any 517 * of the keys currently in the specified map. 518 * 519 * @param m mappings to be stored in this map. 520 * @throws NullPointerException if the specified map is null. 521 */ putAll(Map<? extends K, ? extends V> m)522 public void putAll(Map<? extends K, ? extends V> m) { 523 int numKeysToBeAdded = m.size(); 524 if (numKeysToBeAdded == 0) 525 return; 526 527 /* 528 * Expand the map if the map if the number of mappings to be added 529 * is greater than or equal to threshold. This is conservative; the 530 * obvious condition is (m.size() + size) >= threshold, but this 531 * condition could result in a map with twice the appropriate capacity, 532 * if the keys to be added overlap with the keys already in this map. 533 * By using the conservative calculation, we subject ourself 534 * to at most one extra resize. 535 */ 536 if (numKeysToBeAdded > threshold) { 537 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1); 538 if (targetCapacity > MAXIMUM_CAPACITY) 539 targetCapacity = MAXIMUM_CAPACITY; 540 int newCapacity = table.length; 541 while (newCapacity < targetCapacity) 542 newCapacity <<= 1; 543 if (newCapacity > table.length) 544 resize(newCapacity); 545 } 546 547 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 548 put(e.getKey(), e.getValue()); 549 } 550 551 /** 552 * Removes the mapping for a key from this weak hash map if it is present. 553 * More formally, if this map contains a mapping from key <tt>k</tt> to 554 * value <tt>v</tt> such that <code>(key==null ? k==null : 555 * key.equals(k))</code>, that mapping is removed. (The map can contain 556 * at most one such mapping.) 557 * 558 * <p>Returns the value to which this map previously associated the key, 559 * or <tt>null</tt> if the map contained no mapping for the key. A 560 * return value of <tt>null</tt> does not <i>necessarily</i> indicate 561 * that the map contained no mapping for the key; it's also possible 562 * that the map explicitly mapped the key to <tt>null</tt>. 563 * 564 * <p>The map will not contain a mapping for the specified key once the 565 * call returns. 566 * 567 * @param key key whose mapping is to be removed from the map 568 * @return the previous value associated with <tt>key</tt>, or 569 * <tt>null</tt> if there was no mapping for <tt>key</tt> 570 */ remove(Object key)571 public V remove(Object key) { 572 Object k = maskNull(key); 573 int h = sun.misc.Hashing.singleWordWangJenkinsHash(k); 574 Entry<K,V>[] tab = getTable(); 575 int i = indexFor(h, tab.length); 576 Entry<K,V> prev = tab[i]; 577 Entry<K,V> e = prev; 578 579 while (e != null) { 580 Entry<K,V> next = e.next; 581 if (h == e.hash && eq(k, e.get())) { 582 modCount++; 583 size--; 584 if (prev == e) 585 tab[i] = next; 586 else 587 prev.next = next; 588 return e.value; 589 } 590 prev = e; 591 e = next; 592 } 593 594 return null; 595 } 596 597 /** Special version of remove needed by Entry set */ removeMapping(Object o)598 boolean removeMapping(Object o) { 599 if (!(o instanceof Map.Entry)) 600 return false; 601 Entry<K,V>[] tab = getTable(); 602 Map.Entry<?,?> entry = (Map.Entry<?,?>)o; 603 Object k = maskNull(entry.getKey()); 604 int h = sun.misc.Hashing.singleWordWangJenkinsHash(k); 605 int i = indexFor(h, tab.length); 606 Entry<K,V> prev = tab[i]; 607 Entry<K,V> e = prev; 608 609 while (e != null) { 610 Entry<K,V> next = e.next; 611 if (h == e.hash && e.equals(entry)) { 612 modCount++; 613 size--; 614 if (prev == e) 615 tab[i] = next; 616 else 617 prev.next = next; 618 return true; 619 } 620 prev = e; 621 e = next; 622 } 623 624 return false; 625 } 626 627 /** 628 * Removes all of the mappings from this map. 629 * The map will be empty after this call returns. 630 */ clear()631 public void clear() { 632 // clear out ref queue. We don't need to expunge entries 633 // since table is getting cleared. 634 while (queue.poll() != null) 635 ; 636 637 modCount++; 638 Arrays.fill(table, null); 639 size = 0; 640 641 // Allocation of array may have caused GC, which may have caused 642 // additional entries to go stale. Removing these entries from the 643 // reference queue will make them eligible for reclamation. 644 while (queue.poll() != null) 645 ; 646 } 647 648 /** 649 * Returns <tt>true</tt> if this map maps one or more keys to the 650 * specified value. 651 * 652 * @param value value whose presence in this map is to be tested 653 * @return <tt>true</tt> if this map maps one or more keys to the 654 * specified value 655 */ containsValue(Object value)656 public boolean containsValue(Object value) { 657 if (value==null) 658 return containsNullValue(); 659 660 Entry<K,V>[] tab = getTable(); 661 for (int i = tab.length; i-- > 0;) 662 for (Entry<K,V> e = tab[i]; e != null; e = e.next) 663 if (value.equals(e.value)) 664 return true; 665 return false; 666 } 667 668 /** 669 * Special-case code for containsValue with null argument 670 */ containsNullValue()671 private boolean containsNullValue() { 672 Entry<K,V>[] tab = getTable(); 673 for (int i = tab.length; i-- > 0;) 674 for (Entry<K,V> e = tab[i]; e != null; e = e.next) 675 if (e.value==null) 676 return true; 677 return false; 678 } 679 680 /** 681 * The entries in this hash table extend WeakReference, using its main ref 682 * field as the key. 683 */ 684 private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> { 685 V value; 686 int hash; 687 Entry<K,V> next; 688 689 /** 690 * Creates new entry. 691 */ Entry(Object key, V value, ReferenceQueue<Object> queue, int hash, Entry<K,V> next)692 Entry(Object key, V value, 693 ReferenceQueue<Object> queue, 694 int hash, Entry<K,V> next) { 695 super(key, queue); 696 this.value = value; 697 this.hash = hash; 698 this.next = next; 699 } 700 701 @SuppressWarnings("unchecked") getKey()702 public K getKey() { 703 return (K) WeakHashMap.unmaskNull(get()); 704 } 705 getValue()706 public V getValue() { 707 return value; 708 } 709 setValue(V newValue)710 public V setValue(V newValue) { 711 V oldValue = value; 712 value = newValue; 713 return oldValue; 714 } 715 equals(Object o)716 public boolean equals(Object o) { 717 if (!(o instanceof Map.Entry)) 718 return false; 719 Map.Entry<?,?> e = (Map.Entry<?,?>)o; 720 K k1 = getKey(); 721 Object k2 = e.getKey(); 722 if (k1 == k2 || (k1 != null && k1.equals(k2))) { 723 V v1 = getValue(); 724 Object v2 = e.getValue(); 725 if (v1 == v2 || (v1 != null && v1.equals(v2))) 726 return true; 727 } 728 return false; 729 } 730 hashCode()731 public int hashCode() { 732 K k = getKey(); 733 V v = getValue(); 734 return ((k==null ? 0 : k.hashCode()) ^ 735 (v==null ? 0 : v.hashCode())); 736 } 737 toString()738 public String toString() { 739 return getKey() + "=" + getValue(); 740 } 741 } 742 743 private abstract class HashIterator<T> implements Iterator<T> { 744 private int index; 745 private Entry<K,V> entry = null; 746 private Entry<K,V> lastReturned = null; 747 private int expectedModCount = modCount; 748 749 /** 750 * Strong reference needed to avoid disappearance of key 751 * between hasNext and next 752 */ 753 private Object nextKey = null; 754 755 /** 756 * Strong reference needed to avoid disappearance of key 757 * between nextEntry() and any use of the entry 758 */ 759 private Object currentKey = null; 760 HashIterator()761 HashIterator() { 762 index = isEmpty() ? 0 : table.length; 763 } 764 hasNext()765 public boolean hasNext() { 766 Entry<K,V>[] t = table; 767 768 while (nextKey == null) { 769 Entry<K,V> e = entry; 770 int i = index; 771 while (e == null && i > 0) 772 e = t[--i]; 773 entry = e; 774 index = i; 775 if (e == null) { 776 currentKey = null; 777 return false; 778 } 779 nextKey = e.get(); // hold on to key in strong ref 780 if (nextKey == null) 781 entry = entry.next; 782 } 783 return true; 784 } 785 786 /** The common parts of next() across different types of iterators */ nextEntry()787 protected Entry<K,V> nextEntry() { 788 if (modCount != expectedModCount) 789 throw new ConcurrentModificationException(); 790 if (nextKey == null && !hasNext()) 791 throw new NoSuchElementException(); 792 793 lastReturned = entry; 794 entry = entry.next; 795 currentKey = nextKey; 796 nextKey = null; 797 return lastReturned; 798 } 799 remove()800 public void remove() { 801 if (lastReturned == null) 802 throw new IllegalStateException(); 803 if (modCount != expectedModCount) 804 throw new ConcurrentModificationException(); 805 806 WeakHashMap.this.remove(currentKey); 807 expectedModCount = modCount; 808 lastReturned = null; 809 currentKey = null; 810 } 811 812 } 813 814 private class ValueIterator extends HashIterator<V> { next()815 public V next() { 816 return nextEntry().value; 817 } 818 } 819 820 private class KeyIterator extends HashIterator<K> { next()821 public K next() { 822 return nextEntry().getKey(); 823 } 824 } 825 826 private class EntryIterator extends HashIterator<Map.Entry<K,V>> { next()827 public Map.Entry<K,V> next() { 828 return nextEntry(); 829 } 830 } 831 832 // Views 833 834 private transient Set<Map.Entry<K,V>> entrySet = null; 835 836 /** 837 * Returns a {@link Set} view of the keys contained in this map. 838 * The set is backed by the map, so changes to the map are 839 * reflected in the set, and vice-versa. If the map is modified 840 * while an iteration over the set is in progress (except through 841 * the iterator's own <tt>remove</tt> operation), the results of 842 * the iteration are undefined. The set supports element removal, 843 * which removes the corresponding mapping from the map, via the 844 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, 845 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> 846 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> 847 * operations. 848 */ keySet()849 public Set<K> keySet() { 850 Set<K> ks = keySet; 851 return (ks != null ? ks : (keySet = new KeySet())); 852 } 853 854 private class KeySet extends AbstractSet<K> { iterator()855 public Iterator<K> iterator() { 856 return new KeyIterator(); 857 } 858 size()859 public int size() { 860 return WeakHashMap.this.size(); 861 } 862 contains(Object o)863 public boolean contains(Object o) { 864 return containsKey(o); 865 } 866 remove(Object o)867 public boolean remove(Object o) { 868 if (containsKey(o)) { 869 WeakHashMap.this.remove(o); 870 return true; 871 } 872 else 873 return false; 874 } 875 clear()876 public void clear() { 877 WeakHashMap.this.clear(); 878 } 879 spliterator()880 public Spliterator<K> spliterator() { 881 return new KeySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 882 } 883 } 884 885 /** 886 * Returns a {@link Collection} view of the values contained in this map. 887 * The collection is backed by the map, so changes to the map are 888 * reflected in the collection, and vice-versa. If the map is 889 * modified while an iteration over the collection is in progress 890 * (except through the iterator's own <tt>remove</tt> operation), 891 * the results of the iteration are undefined. The collection 892 * supports element removal, which removes the corresponding 893 * mapping from the map, via the <tt>Iterator.remove</tt>, 894 * <tt>Collection.remove</tt>, <tt>removeAll</tt>, 895 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not 896 * support the <tt>add</tt> or <tt>addAll</tt> operations. 897 */ values()898 public Collection<V> values() { 899 Collection<V> vs = values; 900 return (vs != null) ? vs : (values = new Values()); 901 } 902 903 private class Values extends AbstractCollection<V> { iterator()904 public Iterator<V> iterator() { 905 return new ValueIterator(); 906 } 907 size()908 public int size() { 909 return WeakHashMap.this.size(); 910 } 911 contains(Object o)912 public boolean contains(Object o) { 913 return containsValue(o); 914 } 915 clear()916 public void clear() { 917 WeakHashMap.this.clear(); 918 } 919 spliterator()920 public Spliterator<V> spliterator() { 921 return new ValueSpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 922 } 923 } 924 925 /** 926 * Returns a {@link Set} view of the mappings contained in this map. 927 * The set is backed by the map, so changes to the map are 928 * reflected in the set, and vice-versa. If the map is modified 929 * while an iteration over the set is in progress (except through 930 * the iterator's own <tt>remove</tt> operation, or through the 931 * <tt>setValue</tt> operation on a map entry returned by the 932 * iterator) the results of the iteration are undefined. The set 933 * supports element removal, which removes the corresponding 934 * mapping from the map, via the <tt>Iterator.remove</tt>, 935 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and 936 * <tt>clear</tt> operations. It does not support the 937 * <tt>add</tt> or <tt>addAll</tt> operations. 938 */ entrySet()939 public Set<Map.Entry<K,V>> entrySet() { 940 Set<Map.Entry<K,V>> es = entrySet; 941 return es != null ? es : (entrySet = new EntrySet()); 942 } 943 944 private class EntrySet extends AbstractSet<Map.Entry<K,V>> { iterator()945 public Iterator<Map.Entry<K,V>> iterator() { 946 return new EntryIterator(); 947 } 948 contains(Object o)949 public boolean contains(Object o) { 950 if (!(o instanceof Map.Entry)) 951 return false; 952 Map.Entry<?,?> e = (Map.Entry<?,?>)o; 953 Entry<K,V> candidate = getEntry(e.getKey()); 954 return candidate != null && candidate.equals(e); 955 } 956 remove(Object o)957 public boolean remove(Object o) { 958 return removeMapping(o); 959 } 960 size()961 public int size() { 962 return WeakHashMap.this.size(); 963 } 964 clear()965 public void clear() { 966 WeakHashMap.this.clear(); 967 } 968 deepCopy()969 private List<Map.Entry<K,V>> deepCopy() { 970 List<Map.Entry<K,V>> list = new ArrayList<>(size()); 971 for (Map.Entry<K,V> e : this) 972 list.add(new AbstractMap.SimpleEntry<>(e)); 973 return list; 974 } 975 toArray()976 public Object[] toArray() { 977 return deepCopy().toArray(); 978 } 979 toArray(T[] a)980 public <T> T[] toArray(T[] a) { 981 return deepCopy().toArray(a); 982 } 983 spliterator()984 public Spliterator<Map.Entry<K,V>> spliterator() { 985 return new EntrySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 986 } 987 } 988 989 @SuppressWarnings("unchecked") 990 @Override forEach(BiConsumer<? super K, ? super V> action)991 public void forEach(BiConsumer<? super K, ? super V> action) { 992 Objects.requireNonNull(action); 993 int expectedModCount = modCount; 994 995 Entry<K, V>[] tab = getTable(); 996 for (Entry<K, V> entry : tab) { 997 while (entry != null) { 998 Object key = entry.get(); 999 if (key != null) { 1000 action.accept((K)WeakHashMap.unmaskNull(key), entry.value); 1001 } 1002 entry = entry.next; 1003 1004 if (expectedModCount != modCount) { 1005 throw new ConcurrentModificationException(); 1006 } 1007 } 1008 } 1009 } 1010 1011 @SuppressWarnings("unchecked") 1012 @Override replaceAll(BiFunction<? super K, ? super V, ? extends V> function)1013 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 1014 Objects.requireNonNull(function); 1015 int expectedModCount = modCount; 1016 1017 Entry<K, V>[] tab = getTable(); 1018 for (Entry<K, V> entry : tab) { 1019 while (entry != null) { 1020 Object key = entry.get(); 1021 if (key != null) { 1022 entry.value = function.apply((K)WeakHashMap.unmaskNull(key), entry.value); 1023 } 1024 entry = entry.next; 1025 1026 if (expectedModCount != modCount) { 1027 throw new ConcurrentModificationException(); 1028 } 1029 } 1030 } 1031 } 1032 1033 1034 /** 1035 * Similar form as other hash Spliterators, but skips dead 1036 * elements. 1037 */ 1038 static class WeakHashMapSpliterator<K,V> { 1039 final WeakHashMap<K,V> map; 1040 WeakHashMap.Entry<K,V> current; // current node 1041 int index; // current index, modified on advance/split 1042 int fence; // -1 until first use; then one past last index 1043 int est; // size estimate 1044 int expectedModCount; // for comodification checks 1045 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1046 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin, 1047 int fence, int est, 1048 int expectedModCount) { 1049 this.map = m; 1050 this.index = origin; 1051 this.fence = fence; 1052 this.est = est; 1053 this.expectedModCount = expectedModCount; 1054 } 1055 getFence()1056 final int getFence() { // initialize fence and size on first use 1057 int hi; 1058 if ((hi = fence) < 0) { 1059 WeakHashMap<K,V> m = map; 1060 est = m.size(); 1061 expectedModCount = m.modCount; 1062 hi = fence = m.table.length; 1063 } 1064 return hi; 1065 } 1066 estimateSize()1067 public final long estimateSize() { 1068 getFence(); // force init 1069 return (long) est; 1070 } 1071 } 1072 1073 static final class KeySpliterator<K,V> 1074 extends WeakHashMapSpliterator<K,V> 1075 implements Spliterator<K> { KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1076 KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1077 int expectedModCount) { 1078 super(m, origin, fence, est, expectedModCount); 1079 } 1080 trySplit()1081 public KeySpliterator<K,V> trySplit() { 1082 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1083 return (lo >= mid) ? null : 1084 new KeySpliterator<K,V>(map, lo, index = mid, est >>>= 1, 1085 expectedModCount); 1086 } 1087 forEachRemaining(Consumer<? super K> action)1088 public void forEachRemaining(Consumer<? super K> action) { 1089 int i, hi, mc; 1090 if (action == null) 1091 throw new NullPointerException(); 1092 WeakHashMap<K,V> m = map; 1093 WeakHashMap.Entry<K,V>[] tab = m.table; 1094 if ((hi = fence) < 0) { 1095 mc = expectedModCount = m.modCount; 1096 hi = fence = tab.length; 1097 } 1098 else 1099 mc = expectedModCount; 1100 if (tab.length >= hi && (i = index) >= 0 && 1101 (i < (index = hi) || current != null)) { 1102 WeakHashMap.Entry<K,V> p = current; 1103 current = null; // exhaust 1104 do { 1105 if (p == null) 1106 p = tab[i++]; 1107 else { 1108 Object x = p.get(); 1109 p = p.next; 1110 if (x != null) { 1111 @SuppressWarnings("unchecked") K k = 1112 (K) WeakHashMap.unmaskNull(x); 1113 action.accept(k); 1114 } 1115 } 1116 } while (p != null || i < hi); 1117 } 1118 if (m.modCount != mc) 1119 throw new ConcurrentModificationException(); 1120 } 1121 tryAdvance(Consumer<? super K> action)1122 public boolean tryAdvance(Consumer<? super K> action) { 1123 int hi; 1124 if (action == null) 1125 throw new NullPointerException(); 1126 WeakHashMap.Entry<K,V>[] tab = map.table; 1127 if (tab.length >= (hi = getFence()) && index >= 0) { 1128 while (current != null || index < hi) { 1129 if (current == null) 1130 current = tab[index++]; 1131 else { 1132 Object x = current.get(); 1133 current = current.next; 1134 if (x != null) { 1135 @SuppressWarnings("unchecked") K k = 1136 (K) WeakHashMap.unmaskNull(x); 1137 action.accept(k); 1138 if (map.modCount != expectedModCount) 1139 throw new ConcurrentModificationException(); 1140 return true; 1141 } 1142 } 1143 } 1144 } 1145 return false; 1146 } 1147 characteristics()1148 public int characteristics() { 1149 return Spliterator.DISTINCT; 1150 } 1151 } 1152 1153 static final class ValueSpliterator<K,V> 1154 extends WeakHashMapSpliterator<K,V> 1155 implements Spliterator<V> { ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1156 ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1157 int expectedModCount) { 1158 super(m, origin, fence, est, expectedModCount); 1159 } 1160 trySplit()1161 public ValueSpliterator<K,V> trySplit() { 1162 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1163 return (lo >= mid) ? null : 1164 new ValueSpliterator<K,V>(map, lo, index = mid, est >>>= 1, 1165 expectedModCount); 1166 } 1167 forEachRemaining(Consumer<? super V> action)1168 public void forEachRemaining(Consumer<? super V> action) { 1169 int i, hi, mc; 1170 if (action == null) 1171 throw new NullPointerException(); 1172 WeakHashMap<K,V> m = map; 1173 WeakHashMap.Entry<K,V>[] tab = m.table; 1174 if ((hi = fence) < 0) { 1175 mc = expectedModCount = m.modCount; 1176 hi = fence = tab.length; 1177 } 1178 else 1179 mc = expectedModCount; 1180 if (tab.length >= hi && (i = index) >= 0 && 1181 (i < (index = hi) || current != null)) { 1182 WeakHashMap.Entry<K,V> p = current; 1183 current = null; // exhaust 1184 do { 1185 if (p == null) 1186 p = tab[i++]; 1187 else { 1188 Object x = p.get(); 1189 V v = p.value; 1190 p = p.next; 1191 if (x != null) 1192 action.accept(v); 1193 } 1194 } while (p != null || i < hi); 1195 } 1196 if (m.modCount != mc) 1197 throw new ConcurrentModificationException(); 1198 } 1199 tryAdvance(Consumer<? super V> action)1200 public boolean tryAdvance(Consumer<? super V> action) { 1201 int hi; 1202 if (action == null) 1203 throw new NullPointerException(); 1204 WeakHashMap.Entry<K,V>[] tab = map.table; 1205 if (tab.length >= (hi = getFence()) && index >= 0) { 1206 while (current != null || index < hi) { 1207 if (current == null) 1208 current = tab[index++]; 1209 else { 1210 Object x = current.get(); 1211 V v = current.value; 1212 current = current.next; 1213 if (x != null) { 1214 action.accept(v); 1215 if (map.modCount != expectedModCount) 1216 throw new ConcurrentModificationException(); 1217 return true; 1218 } 1219 } 1220 } 1221 } 1222 return false; 1223 } 1224 characteristics()1225 public int characteristics() { 1226 return 0; 1227 } 1228 } 1229 1230 static final class EntrySpliterator<K,V> 1231 extends WeakHashMapSpliterator<K,V> 1232 implements Spliterator<Map.Entry<K,V>> { EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1233 EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1234 int expectedModCount) { 1235 super(m, origin, fence, est, expectedModCount); 1236 } 1237 trySplit()1238 public EntrySpliterator<K,V> trySplit() { 1239 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1240 return (lo >= mid) ? null : 1241 new EntrySpliterator<K,V>(map, lo, index = mid, est >>>= 1, 1242 expectedModCount); 1243 } 1244 1245 forEachRemaining(Consumer<? super Map.Entry<K, V>> action)1246 public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { 1247 int i, hi, mc; 1248 if (action == null) 1249 throw new NullPointerException(); 1250 WeakHashMap<K,V> m = map; 1251 WeakHashMap.Entry<K,V>[] tab = m.table; 1252 if ((hi = fence) < 0) { 1253 mc = expectedModCount = m.modCount; 1254 hi = fence = tab.length; 1255 } 1256 else 1257 mc = expectedModCount; 1258 if (tab.length >= hi && (i = index) >= 0 && 1259 (i < (index = hi) || current != null)) { 1260 WeakHashMap.Entry<K,V> p = current; 1261 current = null; // exhaust 1262 do { 1263 if (p == null) 1264 p = tab[i++]; 1265 else { 1266 Object x = p.get(); 1267 V v = p.value; 1268 p = p.next; 1269 if (x != null) { 1270 @SuppressWarnings("unchecked") K k = 1271 (K) WeakHashMap.unmaskNull(x); 1272 action.accept 1273 (new AbstractMap.SimpleImmutableEntry<K,V>(k, v)); 1274 } 1275 } 1276 } while (p != null || i < hi); 1277 } 1278 if (m.modCount != mc) 1279 throw new ConcurrentModificationException(); 1280 } 1281 tryAdvance(Consumer<? super Map.Entry<K,V>> action)1282 public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) { 1283 int hi; 1284 if (action == null) 1285 throw new NullPointerException(); 1286 WeakHashMap.Entry<K,V>[] tab = map.table; 1287 if (tab.length >= (hi = getFence()) && index >= 0) { 1288 while (current != null || index < hi) { 1289 if (current == null) 1290 current = tab[index++]; 1291 else { 1292 Object x = current.get(); 1293 V v = current.value; 1294 current = current.next; 1295 if (x != null) { 1296 @SuppressWarnings("unchecked") K k = 1297 (K) WeakHashMap.unmaskNull(x); 1298 action.accept 1299 (new AbstractMap.SimpleImmutableEntry<K,V>(k, v)); 1300 if (map.modCount != expectedModCount) 1301 throw new ConcurrentModificationException(); 1302 return true; 1303 } 1304 } 1305 } 1306 } 1307 return false; 1308 } 1309 characteristics()1310 public int characteristics() { 1311 return Spliterator.DISTINCT; 1312 } 1313 } 1314 1315 } 1316