介绍

内存泄漏检测工具，square公司出品，github地址https://github.com/square/leakcanary。
gradle引用：

debugCompile 'com.squareup.leakcanary:leakcanary-android:1.5'
releaseCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.5'

使用

在自定义application中onCreat方法中调用下面代码。默认只是检测所有activity中的内存泄漏。如果想检测fragment、service等的内存泄漏，需要在相应的类的onDestory方法中调用refWatcher.watch(this)即可。然后在使用app的过程中，如果出现内存泄漏就会在leaks的app中listview展示出来，并且有相应的路径。

  if (LeakCanary.isInAnalyzerProcess(this)) {// This process is dedicated to LeakCanary for heap analysis.// You should not init your app in this process.return;}LeakCanary.install(this);

问题

使用特别简单，但是想了想，有几个问题值得思考。
如何检测到所有activity的内存泄漏的？
内存泄漏检测机制是什么？
内存泄漏轨迹的生成过程？

源码分析

    public static RefWatcher install(Application application) {return refWatcher(application)//创建引用监听者.listenerServiceClass(DisplayLeakService.class)//显示泄漏信息service.excludedRefs(AndroidExcludedRefs.createAppDefaults().build()).buildAndInstall();}

以上为install源码，不难发现buildAndInstall是一个build模式，一般build都是一些校验或者初始化。

    public RefWatcher buildAndInstall() {RefWatcher refWatcher = build();if (refWatcher != DISABLED) {LeakCanary.enableDisplayLeakActivity(context);ActivityRefWatcher.installOnIcsPlus((Application) context, refWatcher);}return refWatcher;}

然后build之后创建一个RefWatcher对象。

    public final RefWatcher build() {if (isDisabled()) {return RefWatcher.DISABLED;}ExcludedRefs excludedRefs = this.excludedRefs;if (excludedRefs == null) {excludedRefs = defaultExcludedRefs();}HeapDump.Listener heapDumpListener = this.heapDumpListener;if (heapDumpListener == null) {heapDumpListener = defaultHeapDumpListener();}DebuggerControl debuggerControl = this.debuggerControl;if (debuggerControl == null) {debuggerControl = defaultDebuggerControl();}HeapDumper heapDumper = this.heapDumper;if (heapDumper == null) {heapDumper = defaultHeapDumper();}WatchExecutor watchExecutor = this.watchExecutor;if (watchExecutor == null) {watchExecutor = defaultWatchExecutor();}GcTrigger gcTrigger = this.gcTrigger;if (gcTrigger == null) {gcTrigger = defaultGcTrigger();}return new RefWatcher(watchExecutor, debuggerControl, gcTrigger, heapDumper, heapDumpListener,excludedRefs);}

创建完对象之后，enableDisplayLeakActivity方法是否展示泄漏activity，最重要的是ActivityRefWatcher.installOnIcsPlus((Application) context, refWatcher)处理。

    @TargetApi(ICE_CREAM_SANDWICH) public final class ActivityRefWatcher {public static void installOnIcsPlus(Application application, RefWatcher refWatcher) {if (SDK_INT < ICE_CREAM_SANDWICH) {// If you need to support Android < ICS, override onDestroy() in your base activity.return;}ActivityRefWatcher activityRefWatcher = new ActivityRefWatcher(application, refWatcher);activityRefWatcher.watchActivities();}private final Application.ActivityLifecycleCallbacks lifecycleCallbacks =new Application.ActivityLifecycleCallbacks() {@Override public void onActivityCreated(Activity activity, Bundle savedInstanceState) {}@Override public void onActivityStarted(Activity activity) {}@Override public void onActivityResumed(Activity activity) {}@Override public void onActivityPaused(Activity activity) {}@Override public void onActivityStopped(Activity activity) {}@Override public void onActivitySaveInstanceState(Activity activity, Bundle outState) {}@Override public void onActivityDestroyed(Activity activity) {ActivityRefWatcher.this.onActivityDestroyed(activity);}};private final Application application;private final RefWatcher refWatcher;/*** Constructs an {@link ActivityRefWatcher} that will make sure the activities     are not leaking* after they have been destroyed.*/public ActivityRefWatcher(Application application, final RefWatcher refWatcher) {this.application = checkNotNull(application, "application");this.refWatcher = checkNotNull(refWatcher, "refWatcher");}void onActivityDestroyed(Activity activity) {refWatcher.watch(activity);}public void watchActivities() {// Make sure you don't get installed twice.stopWatchingActivities();application.registerActivityLifecycleCallbacks(lifecycleCallbacks);}public void stopWatchingActivities() {application.unregisterActivityLifecycleCallbacks(lifecycleCallbacks);}}

installOnIcsPlus方法先判断版本<14 不能使用，然后调用创建ActivityRefWatcher对象，调用watchActivities方法，watchActivities里面就是将传入的application注册registerActivityLifecycleCallbacks用来获取这个application的所有activity的生命周期。然后在Application.ActivityLifecycleCallbacks回调中onActivityDestroyed生命周期里面调用ActivityRefWatcher.this.onActivityDestroyed(activity)方法，最后调用到refWatcher.watch(activity)，接下来进入watch来看下。

    public void watch(Object watchedReference) {watch(watchedReference, "");}public void watch(Object watchedReference, String referenceName) {if (this == DISABLED) {return;}checkNotNull(watchedReference, "watchedReference");checkNotNull(referenceName, "referenceName");final long watchStartNanoTime = System.nanoTime();String key = UUID.randomUUID().toString();retainedKeys.add(key);final KeyedWeakReference reference =new KeyedWeakReference(watchedReference, key, referenceName, queue);ensureGoneAsync(watchStartNanoTime, reference);}

首先根据uuid创建一个key放入retainedKeys数组里面，添加弱引用的标识，KeyedWeakReference是继承WeakReference的类，一个弱引用的封装。看到
new KeyedWeakReference(watchedReference, key, referenceName, queue)，是在创建一个弱引用，并放到ReferenceQueue引用队列中。KeyedWeakReference里面日常参数校验，以及调用WeakReference的super方法。

    final class KeyedWeakReference extends WeakReference<Object> {public final String key;public final String name;KeyedWeakReference(Object referent, String key, String name,ReferenceQueue<Object> referenceQueue) {super(checkNotNull(referent, "referent"), checkNotNull(referenceQueue, "referenceQueue"));this.key = checkNotNull(key, "key");this.name = checkNotNull(name, "name");}}

接下来查看ensureGoneAsync方法。

     private void ensureGoneAsync(final long watchStartNanoTime, final KeyedWeakReference reference) {watchExecutor.execute(new Retryable() {@Override public Retryable.Result run() {return ensureGone(reference, watchStartNanoTime);}});}Retryable.Result ensureGone(final KeyedWeakReference reference, final long watchStartNanoTime) {long gcStartNanoTime = System.nanoTime();long watchDurationMs = NANOSECONDS.toMillis(gcStartNanoTime - watchStartNanoTime);//清除此时已经到ReferenceQueue中的弱引用removeWeaklyReachableReferences();if (debuggerControl.isDebuggerAttached()) {// The debugger can create false leaks.return RETRY;}//没有内存泄漏if (gone(reference)) {return DONE;}//gc处理gcTrigger.runGc();removeWeaklyReachableReferences();//代表内存泄漏if (!gone(reference)) {long startDumpHeap = System.nanoTime();long gcDurationMs = NANOSECONDS.toMillis(startDumpHeap - gcStartNanoTime);File heapDumpFile = heapDumper.dumpHeap();if (heapDumpFile == RETRY_LATER) {// Could not dump the heap.return RETRY;}long heapDumpDurationMs = NANOSECONDS.toMillis(System.nanoTime() - startDumpHeap);//生成hprof文件并进行分析hprof文件heapdumpListener.analyze(new HeapDump(heapDumpFile, reference.key, reference.name, excludedRefs, watchDurationMs,gcDurationMs, heapDumpDurationMs));}return DONE;}

源码大概就是先清除弱引用的队列，然后查看引用是否存在队列中，
.if (gone(reference)) 用来判断某个 reference 的 key 是否仍在 retainedKeys 里，若不在，表示已回收，否则继续。然后在手动gc，之后再清除弱引用，在查看是否弱引用队列中是否存在，如果存在证明有内存泄露，就生成hprof文件并分析hprof文件。
removeWeaklyReachableReferences方法是清除此时已经到ReferenceQueue中的弱引用，gone方法是检测存放key的数组是否存在key。

    private boolean gone(KeyedWeakReference reference) {return !retainedKeys.contains(reference.key);}private void removeWeaklyReachableReferences() {// WeakReferences are enqueued as soon as the object to which they point to becomes weakly// reachable. This is before finalization or garbage collection has actually happened.KeyedWeakReference ref;while ((ref = (KeyedWeakReference) queue.poll()) != null) {retainedKeys.remove(ref.key);}}File heapDumpFile = heapDumper.dumpHeap()，生成hprof文件的具体实现在AndroidHeapDumper类中。public final class AndroidHeapDumper implements HeapDumper {private final Context context;private final LeakDirectoryProvider leakDirectoryProvider;private final Handler mainHandler;public AndroidHeapDumper(Context context, LeakDirectoryProvider   leakDirectoryProvider) {this.leakDirectoryProvider = leakDirectoryProvider;this.context = context.getApplicationContext();mainHandler = new Handler(Looper.getMainLooper());}@Override public File dumpHeap() {File heapDumpFile = leakDirectoryProvider.newHeapDumpFile();if (heapDumpFile == RETRY_LATER) {return RETRY_LATER;}FutureResult<Toast> waitingForToast = new FutureResult<>();showToast(waitingForToast);if (!waitingForToast.wait(5, SECONDS)) {CanaryLog.d("Did not dump heap, too much time waiting for Toast.");return RETRY_LATER;}Toast toast = waitingForToast.get();try {Debug.dumpHprofData(heapDumpFile.getAbsolutePath());cancelToast(toast);return heapDumpFile;} catch (Exception e) {CanaryLog.d(e, "Could not dump heap");// Abort heap dumpreturn RETRY_LATER;}}private void showToast(final FutureResult<Toast> waitingForToast) {mainHandler.post(new Runnable() {@Override public void run() {final Toast toast = new Toast(context);toast.setGravity(Gravity.CENTER_VERTICAL, 0, 0);toast.setDuration(Toast.LENGTH_LONG);LayoutInflater inflater = LayoutInflater.from(context);toast.setView(inflater.inflate(R.layout.leak_canary_heap_dump_toast, null));toast.show();// Waiting for Idle to make sure Toast gets rendered.Looper.myQueue().addIdleHandler(new MessageQueue.IdleHandler() {@Override public boolean queueIdle() {waitingForToast.set(toast);return false;}});}});}private void cancelToast(final Toast toast) {mainHandler.post(new Runnable() {@Override public void run() {toast.cancel();}});}}分析的具体实现在HeapAnalyzerService中，HeapAnalyzerService是一个IntentService。public final class HeapAnalyzerService extends IntentService {private static final String LISTENER_CLASS_EXTRA = "listener_class_extra";private static final String HEAPDUMP_EXTRA = "heapdump_extra";public static void runAnalysis(Context context, HeapDump heapDump,Class<? extends AbstractAnalysisResultService> listenerServiceClass) {Intent intent = new Intent(context, HeapAnalyzerService.class);intent.putExtra(LISTENER_CLASS_EXTRA, listenerServiceClass.getName());intent.putExtra(HEAPDUMP_EXTRA, heapDump);context.startService(intent);}public HeapAnalyzerService() {super(HeapAnalyzerService.class.getSimpleName());}@Override protected void onHandleIntent(Intent intent) {if (intent == null) {CanaryLog.d("HeapAnalyzerService received a null intent, ignoring.");return;}String listenerClassName = intent.getStringExtra(LISTENER_CLASS_EXTRA);HeapDump heapDump = (HeapDump) intent.getSerializableExtra(HEAPDUMP_EXTRA);HeapAnalyzer heapAnalyzer = new HeapAnalyzer(heapDump.excludedRefs);AnalysisResult result = heapAnalyzer.checkForLeak(heapDump.heapDumpFile, heapDump.referenceKey);AbstractAnalysisResultService.sendResultToListener(this, listenerClassName, heapDump, result);}}

总结

如何检测到所有activity的内存泄漏的？
通过application注册registerActivityLifecycleCallbacks，来监听说有activity的生命周期，并在onDestory中监听。

内存泄漏检测机制是什么？
若 Activity 被正常回收，就把activity使用KeyedWeakReference创建一个弱引用，引用它的 KeyedWeakReference 会被自动放入 ReferenceQueue 中。首先先移除不可达用引用，如果当前引用不存在，就不继续了，然后gc，再次移除不可达引用，如果当前引用不存在，就不继续了。如果两次移除后都没有被回收，就根据队列的弱引用，生成HeapDump信息。

内存泄漏轨迹的生成过程？
利用 heapDumper 把内存情况 dump 成文件，利用 HeapAnalyzer 对 dump 的内存情况进行分析并进一步确认，若确定发生泄漏，调用 DisplayLeakService发送通知。

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leakcanary1.5源码分析

文章目录

介绍

使用

问题

源码分析

总结

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