详解LeakCanary分析内存泄露如何实现

dependencies {
    // debugImplementation because LeakCanary should only run in debug builds. 
    debugImplementation 'com.squareup.leakcanary:leakcanary-Android:2.10'
}

<manifest xmlns:android="Http://schemas.android.com/apk/res/android"
    package="com.squareup.leakcanary.objectwatcher" >
    <uses-sdk android:minSdkVersion="14" />
    <application>
        <provider
            android:name="leakcanary.internal.MainProcessAppWatcherInstaller"
            android:authorities="${applicationId}.leakcanary-installer"
            android:enabled="@bool/leak_canary_watcher_auto_install"
            android:exported="false" />
    </application>
</manifest>

fun appDefaultWatchers(
  application: Application,
  reachabilityWatcher: ReachabilityWatcher = objectWatcher
): List<InstallableWatcher> {
  return listOf(
    ActivityWatcher(application, reachabilityWatcher),
    FragmentAndViewModelWatcher(application, reachabilityWatcher),
    RootViewWatcher(reachabilityWatcher),
    ServiceWatcher(reachabilityWatcher)
  )
}

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

private final FragmentManager.FragmentLifecycleCallbacks fragmentLifecycleCallbacks =
    new FragmentManager.FragmentLifecycleCallbacks() {
      @Override public void onFragmentViewDestroyed(FragmentManager fm, Fragment fragment) {
        View view = fragment.getView();
        if (view != null) {
          refWatcher.watch(view);
        }
      }
      @Override
      public void onFragmentDestroyed(FragmentManager fm, Fragment fragment) {
        refWatcher.watch(fragment);
      }
    };

private val listener = OnRootViewAddedListener { rootView ->
  val trackDetached = when(rootView.windowType) {
    PHONE_WINDOW -> {
      when (rootView.phoneWindow?.callback?.wrappedCallback) {
        is Activity -> false
        is Dialog -> {
          ......
        }
        else -> true
      }
    }
    POPUP_WINDOW -> false
    TOOLTIP, TOAST, UNKNOWN -> true
  }
  if (trackDetached) {
    rootView.addOnAttachStateChangeListener(object : OnAttachStateChangeListener {
      val watchDetachedView = Runnable {
        reachabilityWatcher.expectWeaklyReachable(
          rootView, "${rootView::class.java.name} received View#onDetachedFromWindow() callback"
        )
      }
        ......
    })
  }
}

@Synchronized override fun expectWeaklyReachable(
  watchedObject: Any,
  description: String
) {
  // 先从queue中移除一次已回收对象
  removeWeaklyReachableObjects()
  // 生成随机数当成key
  val key = UUID.randomUUID().toString()
  val watchUptimeMillis = clock.uptimeMillis()
  // 创建弱引用关联ReferenceQueue
  val reference =
    KeyedWeakReference(watchedObject, key, description, watchUptimeMillis, queue)
  ......
  // 把reference和key 添加到一个Map中
  watchedObjects[key] = reference
  // 下一步
  checkRetainedExecutor.execute {
    moveToRetained(key)
  }
}

public void watch(Object watchedReference, String referenceName) {
        ......
        // 生成随机数当成key
        String key = UUID.randomUUID().toString();
        // 把key 添加到一个Set中
        this.retainedKeys.add(key);
        // 创建弱引用关联ReferenceQueue
        KeyedWeakReference reference = new KeyedWeakReference(watchedReference, key, referenceName, this.queue);
        // 下一步
        this.ensureGoneAsync(watchStartNanoTime, reference);
}

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

private void waitForIdle(final Retryable retryable, final int failedAttempts) {
  // 使用IdleHandler来实现在闲时才去执行后面的流程
  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;
  // 根据上下文去计算，这里是5秒
  backgroundHandler.postDelayed(new Runnable() {
    @Override public void run() {
      Retryable.Result result = retryable.run();
      if (result == RETRY) {
        postWaitForIdle(retryable, failedAttempts + 1);
      }
    }
  }, delayMillis);
}

@Synchronized private fun moveToRetained(key: String) {
  // 从ReferenceQueue中拿出对象移除
  removeWeaklyReachableObjects()
  // 经过上一步之后判断Map中还有没有这个key，有的话进入下一步操作
  val retainedRef = watchedObjects[key]
  if (retainedRef != null) {
    retainedRef.retainedUptimeMillis = clock.uptimeMillis()
    onObjectRetainedListeners.forEach { it.onObjectRetained() }
  }
}
private fun removeWeaklyReachableObjects() {
  // 从ReferenceQueue中拿出对象，然后从Map中移除
  var ref: KeyedWeakReference?
  do {
    ref = queue.poll() as KeyedWeakReference?
    if (ref != null) {
      watchedObjects.remove(ref.key)
    }
  } while (ref != null)
}