1 /* 2 * Copyright (c) Facebook, Inc. and its affiliates. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.facebook.jni; 18 19 import com.facebook.jni.annotations.DoNotStripAny; 20 21 /** 22 * This object holds a native C++ member for hybrid Java/C++ objects. 23 * 24 * <p>NB: THREAD SAFETY 25 * 26 * <p>{@link #resetNative} deletes the corresponding native object synchronously on whatever thread 27 * the method is called on. Otherwise, deletion will occur on the {@link DestructorThread} thread. 28 */ 29 @DoNotStripAny 30 public class HybridData { 31 32 static { 33 System.loadLibrary("fbjni"); 34 } 35 36 private final Destructor mDestructor = new Destructor(this); 37 38 /** 39 * To explicitly delete the instance, call resetNative(). If the C++ instance is referenced after 40 * this is called, a NullPointerException will be thrown. resetNative() may be called multiple 41 * times safely. Because the {@link DestructorThread} also calls resetNative, the instance will 42 * not leak if this is not called, but timing of deletion and the thread the C++ dtor is called on 43 * will be at the whim of the Java GC. If you want to control the thread and timing of the 44 * destructor, you should call resetNative() explicitly. 45 */ resetNative()46 public synchronized void resetNative() { 47 mDestructor.destruct(); 48 } 49 50 /** 51 * N.B. Thread safety. If you call isValid from a different thread than {@link #resetNative()} 52 * then be sure to do so while synchronizing on the hybrid. For example: 53 * 54 * <pre><code> 55 * synchronized(hybrid) { 56 * if (hybrid.isValid) { 57 * // Do stuff. 58 * } 59 * } 60 * </code></pre> 61 */ isValid()62 public boolean isValid() { 63 return mDestructor.mNativePointer != 0; 64 } 65 66 @DoNotStripAny 67 public static class Destructor extends DestructorThread.Destructor { 68 69 // Private C++ instance 70 private volatile long mNativePointer; 71 Destructor(Object referent)72 Destructor(Object referent) { 73 super(referent); 74 } 75 76 @Override destruct()77 protected final void destruct() { 78 // When invoked from the DestructorThread instead of resetNative, 79 // the DestructorThread has exclusive ownership of the HybridData 80 // so synchronization is not necessary. 81 deleteNative(mNativePointer); 82 mNativePointer = 0; 83 } 84 deleteNative(long pointer)85 static native void deleteNative(long pointer); 86 } 87 } 88