2020漫画系统源码(漫画安卓：LeakCanary源码解析)

LeakCanary.install(this)源码如下所示：public static RefWatcher install(Application application) { return ((AndroidRefWatcherBuilder)refWatcher(application).listenerServiceClass(DisplayLeakService.class).excludedRefs(AndroidExcludedRefs.createAppDefaults().build())).buildAndInstall(); }

listenerServiceClass(DisplayLeakService.class)：用于分析内存泄漏结果信息，然后发送通知给用户 excludedRefs(AndroidExcludedRefs.createAppDefaults().build())：设置需要忽略的对象，比如某些系统漏洞不需要统计。

buildAndInstall()：真正检测内存泄漏的方法，下面将展开分析该方法public RefWatcher buildAndInstall() { RefWatcher refWatcher = this.build(); if(refWatcher != RefWatcher.DISABLED) { LeakCanary.enableDisplayLeakActivity(this.context); ActivityRefWatcher.installOnIcsPlus((Application)this.context, refWatcher); } return refWatcher; }

可以看到，上面方法主要做了三件事情： 1.实例化RefWatcher对象，该对象主要作用是检测是否有对象未被回收导致内存泄漏； 2.设置APP图标可见； 3.检测内存

RefWatcher的使用后面讲，这边主要看第二件事情的处理过程，及enableDisplayLeakActivity方法的源码public static void enableDisplayLeakActivity(Context context) { LeakCanaryInternals.setEnabled(context, DisplayLeakActivity.class, true); } public static void setEnabled(Context context, final Class componentClass, final boolean enabled) { final Context appContext = context.getApplicationContext(); executeOnFileIoThread(new Runnable() { public void run() { LeakCanaryInternals.setEnabledBlocking(appContext, componentClass, enabled); } }); } public static void setEnabledBlocking(Context appContext, Class componentClass, boolean enabled) { ComponentName component = new ComponentName(appContext, componentClass); PackageManager packageManager = appContext.getPackageManager(); int newState = enabled?1:2; packageManager.setComponentEnabledSetting(component, newState, 1); }

可见，最后调用packageManager.setComponentEnabledSetting（）方法，实现应用图标的隐藏和显示。

接下来，进入真正的内存检查的方法installOnIcsPlus（）public static void installOnIcsPlus(Application application, RefWatcher refWatcher) { if(VERSION.SDK_INT >= 14) { ActivityRefWatcher activityRefWatcher = new ActivityRefWatcher(application, refWatcher); activityRefWatcher.watchActivities(); } }

该方法实例化出ActivityRefWatcher 对象，该对象用来监听activity的生命周期，具体实现如下所示：public void watchActivities() { this.stopWatchingActivities(); this.application.registerActivityLifecycleCallbacks(this.lifecycleCallbacks); } private final ActivityLifecycleCallbacks lifecycleCallbacks = new ActivityLifecycleCallbacks() { public void onActivityCreated(Activity activity, Bundle savedInstanceState) { } public void onActivityStarted(Activity activity) { } public void onActivityResumed(Activity activity) { } public void onActivityPaused(Activity activity) { } public void onActivityStopped(Activity activity) { } public void onActivitySaveInstanceState(Activity activity, Bundle outState) { } public void onActivityDestroyed(Activity activity) { ActivityRefWatcher.this.onActivityDestroyed(activity); } };

调用了registerActivityLifecycleCallbacks方法后，当Activity执行onDestroy方法后，会触发ActivityLifecycleCallbacks 的onActivityDestroyed方法，在当前方法中，调用refWatcher的watch方法，前面已经讲过RefWatcher对象主要作用是检测是否有对象未被回收导致内存泄漏。

下面继续看refWatcher的watch方法源码：public void watch(Object watchedReference) { this.watch(watchedReference, ""); } public void watch(Object watchedReference, String referenceName) { if(this != DISABLED) { Preconditions.checkNotNull(watchedReference, "watchedReference"); Preconditions.checkNotNull(referenceName, "referenceName"); long watchStartNanoTime = System.nanoTime(); String key = UUID.randomUUID().toString(); this.retainedKeys.add(key); KeyedWeakReference reference = new KeyedWeakReference(watchedReference, key, referenceName, this.queue); this.ensureGoneAsync(watchStartNanoTime, reference); } }

可以看到，上面方法主要做了三件事情： 1.生成一个随机数key存放在retainedKeys集合中，用来判断对象是否被回收； 2.把当前Activity放到KeyedWeakReference（WeakReference的子类）中； 3.通过查找ReferenceQueue，看该Acitivity是否存在，存在则证明可以被正常回收，不存在则证明可能存在内存泄漏。

前两件事很简单，这边主要看第三件事情的处理过程，及ensureGoneAsync方法的源码：private void ensureGoneAsync(final long watchStartNanoTime, final KeyedWeakReference reference) { this.watchExecutor.execute(new Retryable() { public Result run() { return RefWatcher.this.ensureGone(reference, watchStartNanoTime); } }); } Result ensureGone(KeyedWeakReference reference, long watchStartNanoTime) { long gcStartNanoTime = System.nanoTime(); long watchDurationMs = TimeUnit.NANOSECONDS.toMillis(gcStartNanoTime - watchStartNanoTime); this.removeWeaklyReachableReferences(); if(this.debuggerControl.isDebuggerAttached()) { return Result.RETRY; } else if(this.gone(reference)) { return Result.DONE; } else { this.gcTrigger.runGc(); this.removeWeaklyReachableReferences(); if(!this.gone(reference)) { long startDumpHeap = System.nanoTime(); long gcDurationMs = TimeUnit.NANOSECONDS.toMillis(startDumpHeap - gcStartNanoTime); File heapDumpFile = this.heapDumper.dumpHeap(); if(heapDumpFile == HeapDumper.RETRY_LATER) { return Result.RETRY; } long heapDumpDurationMs = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startDumpHeap); this.heapdumpListener.analyze(new HeapDump(heapDumpFile, reference.key, reference.name, this.excludedRefs, watchDurationMs, gcDurationMs, heapDumpDurationMs)); } return Result.DONE; } }

该方法中首先执行removeWeaklyReachableReferences()，从ReferenceQueue队列中查询是否存在该弱引用对象，如果不为空，则说明已经被系统回收了，则将对应的随机数key从retainedKeys集合中删除。

private void removeWeaklyReachableReferences() { KeyedWeakReference ref; while((ref = (KeyedWeakReference)this.queue.poll()) != null) { this.retainedKeys.remove(ref.key); } }

然后通过判断retainedKeys集合中是否存在对应的key判断该对象是否被回收private boolean gone(KeyedWeakReference reference) { return !this.retainedKeys.contains(reference.key); }。

如果没有被系统回收，则手动调用gcTrigger.runGc();后再调用removeWeaklyReachableReferences方法判断该对象是否被回收GcTrigger DEFAULT = new GcTrigger() { public void runGc() { Runtime.getRuntime().gc(); this.enqueueReferences(); System.runFinalization(); } private void enqueueReferences() { try { Thread.sleep(100L); } catch (InterruptedException var2) { throw new AssertionError(); } } };。

第三行代码为手动触发GC，紧接着线程睡100毫秒，给系统回收的时间，随后通过System.runFinalization()手动调用已经失去引用对象的finalize方法 通过手动GC该对象还不能被回收的话，则存在内存泄漏，调用heapDumper.dumpHeap()生成.hprof文件目录，并通过heapdumpListener回调到analyze()方法，后面关于dump文件的分析这边就不介绍了，感兴趣的可以自行去看。

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