Leakcanary流程分析

Leakcanary 是我们Android开发中检查内存泄漏的利器。之前有看过源码不太记得了再回顾一遍并记录下来。

用法很简单，在我们自定义的Application中的onCreate函数中调用LeakCanary.install(this);

public static RefWatcher install(Application application) {
    return refWatcher(application).listenerServiceClass(DisplayLeakService.class)
        .excludedRefs(AndroidExcludedRefs.createAppDefaults().build())
        .buildAndInstall();
  }

refWatcher返回了一个RefWatcher对象，之后就是通过建造者模式配置一些参数。

第一个配置项：DisplayLeakService.class，首先根据名字就能够知道这是个服务。这个服务里面主要处理hrof文件的解析，就是对内存泄漏引用链的分析。

第二个配置项：配置的是我们想要忽略掉的，排除掉的内存泄漏。默认的里面主要是Android系统内部的一些内存泄漏的地方。当然我们也可以配置自己想要忽略的地方。

通过创建符合您的需求的EnumSet并调用createBuilder(EnumSet)来选择要忽略的泄漏。

public RefWatcher buildAndInstall() {
    if (LeakCanaryInternals.installedRefWatcher != null) {
      throw new UnsupportedOperationException("buildAndInstall() should only be called once.");
    }
    RefWatcher refWatcher = build();
    if (refWatcher != DISABLED) {
      if (watchActivities) {
        ActivityRefWatcher.install(context, refWatcher);
      }
      if (watchFragments) {
        FragmentRefWatcher.Helper.install(context, refWatcher);
      }
    }
    LeakCanaryInternals.installedRefWatcher = refWatcher;
    return refWatcher;
  }

private boolean watchActivities = true;
  private boolean watchFragments = true;

这两个参数默认就是true，就是分别进入ActivityRefWatcher.install(context, refWatcher);和FragmentRefWatcher.Helper.install(context, refWatcher);。当然也可以通过方法配置是否要监控activity或者fragment的内存泄漏情况。

首先看对activity的处理，

public static void install(Context context, RefWatcher refWatcher) {
    Application application = (Application) context.getApplicationContext();
    ActivityRefWatcher activityRefWatcher = new ActivityRefWatcher(application, refWatcher);

    application.registerActivityLifecycleCallbacks(activityRefWatcher.lifecycleCallbacks);
  }

private final Application.ActivityLifecycleCallbacks lifecycleCallbacks =
      new ActivityLifecycleCallbacksAdapter() {
        @Override public void onActivityDestroyed(Activity activity) {
          refWatcher.watch(activity);
        }
      };

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);
  }

可以看出，通过注册activity的生命周期回调，在onDestory方法中处理的。首先使用activity对象创建一个弱引用对象（弱引用：只有弱引用引用到该对象的时候，gc扫描到该对象就会将该对象回收掉），并且根据当前时间创建了一个key并将该key添加到set集合中，因为之后对象释放后要将key移除掉。

private void ensureGoneAsync(final long watchStartNanoTime, final KeyedWeakReference reference) {
    watchExecutor.execute(new Retryable() {
      @Override public Retryable.Result run() {
        return ensureGone(reference, watchStartNanoTime);
      }
    });
  }

watExecutor一眼看到还以为是线程池，其实不然，实际的对象是AndroidWatchExecutor，下面是它核心的函数：

@Override public void execute(Retryable retryable) {
    if (Looper.getMainLooper().getThread() == Thread.currentThread()) {
      waitForIdle(retryable, 0);
    } else {
      postWaitForIdle(retryable, 0);
    }
  }

  private void postWaitForIdle(final Retryable retryable, final int failedAttempts) {
    mainHandler.post(new Runnable() {
      @Override public void run() {
        waitForIdle(retryable, failedAttempts);
      }
    });
  }

  private void waitForIdle(final Retryable retryable, final int failedAttempts) {
    // This needs to be called from the main thread.
    Looper.myQueue().addIdleHandler(new MessageQueue.IdleHandler() {
      @Override public boolean queueIdle() {
        postToBackgroundWithDelay(retryable, failedAttempts);
        return false;
      }
    });
  }

  private void postToBackgroundWithDelay(final Retryable retryable, final int failedAttempts) {
    long exponentialBackoffFactor = (long) Math.min(Math.pow(2, failedAttempts), maxBackoffFactor);
    long delayMillis = initialDelayMillis * exponentialBackoffFactor;
    backgroundHandler.postDelayed(new Runnable() {
      @Override public void run() {
        Retryable.Result result = retryable.run();
        if (result == RETRY) {
          postWaitForIdle(retryable, failedAttempts + 1);
        }
      }
    }, delayMillis);
  }

简单来说就是会在主线程空闲的时候执行Retryable对象中的run方法，看下实际的run方法：

Retryable.Result ensureGone(final KeyedWeakReference reference, final long watchStartNanoTime) {
    long gcStartNanoTime = System.nanoTime();
    long watchDurationMs = NANOSECONDS.toMillis(gcStartNanoTime - watchStartNanoTime);

    removeWeaklyReachableReferences();

    if (debuggerControl.isDebuggerAttached()) {
      // The debugger can create false leaks.
      return RETRY;
    }
    if (gone(reference)) {
      return DONE;
    }
    gcTrigger.runGc();
    removeWeaklyReachableReferences();
    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);

      HeapDump heapDump = heapDumpBuilder.heapDumpFile(heapDumpFile).referenceKey(reference.key)
          .referenceName(reference.name)
          .watchDurationMs(watchDurationMs)
          .gcDurationMs(gcDurationMs)
          .heapDumpDurationMs(heapDumpDurationMs)
          .build();

      heapdumpListener.analyze(heapDump);
    }
    return DONE;
  }

这个方法就是核心了，首先是removeWeaklyReachableReferences函数：

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);
    }
  }

首先会将弱引用队列中的引用对象移除掉，并将key从上面的set集合中去除。

第二步：

private boolean gone(KeyedWeakReference reference) {
    return !retainedKeys.contains(reference.key);
  }

判断set集合中有没有该对象的key，如果没有的话说明该对象已经释放掉了。

第三部，重点，gcTrigger.runGc();

GcTrigger DEFAULT = new GcTrigger() {
    @Override public void runGc() {
      // Code taken from AOSP FinalizationTest:
      // https://android.googlesource.com/platform/libcore/+/master/support/src/test/java/libcore/
      // java/lang/ref/FinalizationTester.java
      // System.gc() does not garbage collect every time. Runtime.gc() is
      // more likely to perfom a gc.
      Runtime.getRuntime().gc();
      enqueueReferences();
      System.runFinalization();
    }

    private void enqueueReferences() {
      // Hack. We don't have a programmatic way to wait for the reference queue daemon to move
      // references to the appropriate queues.
      try {
        Thread.sleep(100);
      } catch (InterruptedException e) {
        throw new AssertionError();
      }
    }
  };

在runGc函数中，手动执行下gc，然后sleep100毫秒，等待gc执行。

System.runFinalization();这一步我的理解是执行如果对象重写了Finalization函数的话就会执行，对象就有可能会复活。

gc执行完毕之后，再次将引用队列中的已经被回收的对象的弱引用移除掉，并将key从set集合中移除掉。

到这一步的时候，没有内存泄漏问题的对象就已经被释放掉了，有问题的对象就还在内存中。

接下来：

@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;
    }

    Notification.Builder builder = new Notification.Builder(context)
        .setContentTitle(context.getString(R.string.leak_canary_notification_dumping));
    Notification notification = LeakCanaryInternals.buildNotification(context, builder);
    NotificationManager notificationManager =
        (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
    int notificationId = (int) SystemClock.uptimeMillis();
    notificationManager.notify(notificationId, notification);

    Toast toast = waitingForToast.get();
    try {
      Debug.dumpHprofData(heapDumpFile.getAbsolutePath());
      cancelToast(toast);
      notificationManager.cancel(notificationId);
      return heapDumpFile;
    } catch (Exception e) {
      CanaryLog.d(e, "Could not dump heap");
      // Abort heap dump
      return RETRY_LATER;
    }
  }

这个函数只用看Debug.dumpHprofData(heapDumpFile.getAbsolutePath());这绝代吗就行了，上面的代码处理了之前的文件的清理和新文件的创建以及通知的创建。

public static void dumpHprofData(String fileName) throws IOException {
        VMDebug.dumpHprofData(fileName);
    }

该函数就会将当前的内存情况进行堆转储了，内存情况写在输入的文件名中是hrof格式的，就和我们在Android studio中的profile中点击按钮生成的一样。

回过头来看ensureGone的接下来的内容：

HeapDump heapDump = heapDumpBuilder.heapDumpFile(heapDumpFile).referenceKey(reference.key)
          .referenceName(reference.name)
          .watchDurationMs(watchDurationMs)
          .gcDurationMs(gcDurationMs)
          .heapDumpDurationMs(heapDumpDurationMs)
          .build();

      heapdumpListener.analyze(heapDump);

创建HelpDump对象

@Override public void analyze(HeapDump heapDump) {
    checkNotNull(heapDump, "heapDump");
    HeapAnalyzerService.runAnalysis(context, heapDump, listenerServiceClass);
  }

public static void runAnalysis(Context context, HeapDump heapDump,
      Class<? extends AbstractAnalysisResultService> listenerServiceClass) {
    setEnabledBlocking(context, HeapAnalyzerService.class, true);
    setEnabledBlocking(context, listenerServiceClass, true);
    Intent intent = new Intent(context, HeapAnalyzerService.class);
    intent.putExtra(LISTENER_CLASS_EXTRA, listenerServiceClass.getName());
    intent.putExtra(HEAPDUMP_EXTRA, heapDump);
    ContextCompat.startForegroundService(context, intent);
  }

@Override protected void onHandleIntentInForeground(@Nullable 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, this, heapDump.reachabilityInspectorClasses);

    AnalysisResult result = heapAnalyzer.checkForLeak(heapDump.heapDumpFile, heapDump.referenceKey,
        heapDump.computeRetainedHeapSize);
    AbstractAnalysisResultService.sendResultToListener(this, listenerClassName, heapDump, result);
  }

在listener中会开启一个IntentService，最终会执行到onHandleIntentInForeground函数中。

在这个函数中，从intent中取到文件名，创建分析工具类HeapAnalyzer，这个类里面的内容很多也比较复杂。感兴趣的可以翻一翻。

@Override protected final void onHandleIntentInForeground(Intent intent) {
    HeapDump heapDump = (HeapDump) intent.getSerializableExtra(HEAP_DUMP_EXTRA);
    AnalysisResult result = (AnalysisResult) intent.getSerializableExtra(RESULT_EXTRA);
    try {
      onHeapAnalyzed(heapDump, result);
    } finally {
      //noinspection ResultOfMethodCallIgnored
      heapDump.heapDumpFile.delete();
    }
  }

分析完hprof文件后，就将分析的结果传入到DisplayLeakService中。

@Override protected final void onHeapAnalyzed(HeapDump heapDump, AnalysisResult result) {
    String leakInfo = leakInfo(this, heapDump, result, true);
    CanaryLog.d("%s", leakInfo);

    boolean resultSaved = false;
    boolean shouldSaveResult = result.leakFound || result.failure != null;
    if (shouldSaveResult) {
      heapDump = renameHeapdump(heapDump);
      resultSaved = saveResult(heapDump, result);
    }

    PendingIntent pendingIntent;
    String contentTitle;
    String contentText;

    if (!shouldSaveResult) {
      contentTitle = getString(R.string.leak_canary_no_leak_title);
      contentText = getString(R.string.leak_canary_no_leak_text);
      pendingIntent = null;
    } else if (resultSaved) {
      pendingIntent = DisplayLeakActivity.createPendingIntent(this, heapDump.referenceKey);

      if (result.failure == null) {
        if (result.retainedHeapSize == AnalysisResult.RETAINED_HEAP_SKIPPED) {
          String className = classSimpleName(result.className);
          if (result.excludedLeak) {
            contentTitle = getString(R.string.leak_canary_leak_excluded, className);
          } else {
            contentTitle = getString(R.string.leak_canary_class_has_leaked, className);
          }
        } else {
          String size = formatShortFileSize(this, result.retainedHeapSize);
          String className = classSimpleName(result.className);
          if (result.excludedLeak) {
            contentTitle = getString(R.string.leak_canary_leak_excluded_retaining, className, size);
          } else {
            contentTitle =
                getString(R.string.leak_canary_class_has_leaked_retaining, className, size);
          }
        }
      } else {
        contentTitle = getString(R.string.leak_canary_analysis_failed);
      }
      contentText = getString(R.string.leak_canary_notification_message);
    } else {
      contentTitle = getString(R.string.leak_canary_could_not_save_title);
      contentText = getString(R.string.leak_canary_could_not_save_text);
      pendingIntent = null;
    }
    // New notification id every second.
    int notificationId = (int) (SystemClock.uptimeMillis() / 1000);
    showNotification(this, contentTitle, contentText, pendingIntent, notificationId);
    afterDefaultHandling(heapDump, result, leakInfo);
  }

主要是创建了通知Notification，DisplayLeakActivity.createPendingIntent(this, heapDump.referenceKey);，从这行代码可得知，点击notification的话就会跳转到DisplayLeakActivity类中了。就是我们查看内存泄漏引用链的页面。

在DisplayLeakActivity中就通过Listview展示分析的结果了。

本文地址：https://blog.csdn.net/qq_28302795/article/details/114325647