Android 進階實現性能優化之OOM與Leakcanary詳解原理

//  leakcanary 添加支持庫即可，隻在debug下使用
debugImplementation 'com.squareup.leakcanary:leakcanary-android:2.3'

//	package="com.squareup.leakcanary.leaksentry"
  <application>
    <provider
        android:name="leakcanary.internal.LeakSentryInstaller"
        android:authorities="${applicationId}.leak-sentry-installer"
        android:exported="false"/>
  </application>

internal class LeakSentryInstaller : ContentProvider() {

  override fun onCreate(): Boolean {
    CanaryLog.logger = DefaultCanaryLog()
    val application = context!!.applicationContext as Application
     // 進行初始化工作，核心
    InternalLeakSentry.install(application)
    return true
  }

  fun install(application: Application) {
    CanaryLog.d("Installing LeakSentry")
    // 隻能在主線程調用，否則會拋出異常
    checkMainThread()
    if (this::application.isInitialized) {
      return
    }
    InternalLeakSentry.application = application

    val configProvider = { LeakSentry.config }
    // 監聽 Activity.onDestroy()
    ActivityDestroyWatcher.install(
        application, refWatcher, configProvider
    )
    // 監聽 Fragment.onDestroy()
    FragmentDestroyWatcher.install(
        application, refWatcher, configProvider
    )
    // Sentry 哨兵
    listener.onLeakSentryInstalled(application)
  }

// ActivityLifecycleCallbacks 接口
public interface ActivityLifecycleCallbacks {
    void onActivityCreated(Activity var1, Bundle var2);

    void onActivityStarted(Activity var1);

    void onActivityResumed(Activity var1);

    void onActivityPaused(Activity var1);

    void onActivityStopped(Activity var1);

    void onActivitySaveInstanceState(Activity var1, Bundle var2);

    void onActivityDestroyed(Activity var1);
}
// FragmentLifecycleCallbacks 接口
public abstract static class FragmentLifecycleCallbacks {

    public void onFragmentCreated(FragmentManager fm, Fragment f, Bundle savedInstanceState) {}

    public void onFragmentViewDestroyed(FragmentManager fm, Fragment f) {}

    public void onFragmentDestroyed(FragmentManager fm, Fragment f) {}

    // 省略其他的生命周期 ...
  }

internal class ActivityDestroyWatcher private constructor(
  private val refWatcher: RefWatcher,
  private val configProvider: () -> Config
) {

  private val lifecycleCallbacks = object : ActivityLifecycleCallbacksAdapter() {
    override fun onActivityDestroyed(activity: Activity) {
      if (configProvider().watchActivities) {
        // 監聽到 onDestroy() 之後，通過 refWatcher 監測 Activity
        refWatcher.watch(activity)
      }
    }
  }

  companion object {
    fun install(
      application: Application,
      refWatcher: RefWatcher,
      configProvider: () -> Config
    ) {
      val activityDestroyWatcher =
        ActivityDestroyWatcher(refWatcher, configProvider)
      // 註冊 Activity 生命周期監聽
      application.registerActivityLifecycleCallbacks(activityDestroyWatcher.lifecycleCallbacks)
    }
  }
}

  @Synchronized fun watch(
    watchedReference: Any,
    referenceName: String
  ) {
    if (!isEnabled()) {
      return
    }
    // 移除隊列中將要被 GC 的引用
    removeWeaklyReachableReferences() 
    val key = UUID.randomUUID().toString()
    val watchUptimeMillis = clock.uptimeMillis()
    // 構建當前引用的弱引用對象，並關聯引用隊列 queue
    val reference = KeyedWeakReference(watchedReference, key, referenceName, watchUptimeMillis, queue)
    if (referenceName != "") {
      CanaryLog.d(
          "Watching instance of %s named %s with key %s", reference.className,
          referenceName, key
      )
    } else {
      CanaryLog.d(
          "Watching instance of %s with key %s", reference.className, key
      )
    }
    // 將引用存入 watchedReferences
    watchedReferences[key] = reference 
    checkRetainedExecutor.execute {
      // 如果當前引用未被移除，仍在 watchedReferences  隊列中，
      // 說明仍未被 GC，移入 retainedReferences 隊列中,暫時標記為泄露
      moveToRetained(key) 
    }
  }

  private fun 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.
    // 弱引用一旦變得弱可達，就會立即入隊。這將在 finalization 或者 GC 之前發生。
    var ref: KeyedWeakReference?
    do {
      // 隊列 queue 中的對象都是會被 GC 的
      ref = queue.poll() as KeyedWeakReference? 
      //說明被釋放瞭
      if (ref != null) {
        val removedRef = watchedReferences.remove(ref.key)//獲取被釋放的引用的key
        if (removedRef == null) {
          retainedReferences.remove(ref.key)
        }
        // 移除 watchedReferences 隊列中的會被 GC 的 ref 對象，剩下的就是可能泄露的對象
      }
    } while (ref != null)
  }

  @Synchronized private fun moveToRetained(key: String) {
    // 再次調用，防止遺漏
    removeWeaklyReachableReferences() 
    val retainedRef = watchedReferences.remove(key)
    //說明可能存在內存泄漏
    if (retainedRef != null) {
      retainedReferences[key] = retainedRef
      onReferenceRetained()
    }
  }

  private fun checkRetainedInstances(reason: String) {
    CanaryLog.d("Checking retained instances because %s", reason)
    val config = configProvider()
    // A tick will be rescheduled when this is turned back on.
    if (!config.dumpHeap) {
      return
    }

    var retainedKeys = refWatcher.retainedKeys

    // 當前泄露實例個數小於 5 個，不進行 heap dump
    if (checkRetainedCount(retainedKeys, config.retainedVisibleThreshold)) return

    if (!config.dumpHeapWhenDebugging && DebuggerControl.isDebuggerAttached) {
      showRetainedCountWithDebuggerAttached(retainedKeys.size)
      scheduleRetainedInstanceCheck("debugger was attached", WAIT_FOR_DEBUG_MILLIS)
      CanaryLog.d(
          "Not checking for leaks while the debugger is attached, will retry in %d ms",
          WAIT_FOR_DEBUG_MILLIS
      )
      return
    }

    // 可能存在被觀察的引用將要變得弱可達，但是還未入隊引用隊列。
    // 這時候應該主動調用一次 GC，可能可以避免一次 heap dump
    gcTrigger.runGc()

    retainedKeys = refWatcher.retainedKeys

    if (checkRetainedCount(retainedKeys, config.retainedVisibleThreshold)) return

    HeapDumpMemoryStore.setRetainedKeysForHeapDump(retainedKeys)

    CanaryLog.d("Found %d retained references, dumping the heap", retainedKeys.size)
    HeapDumpMemoryStore.heapDumpUptimeMillis = SystemClock.uptimeMillis()
    dismissNotification()
    val heapDumpFile = heapDumper.dumpHeap() // AndroidHeapDumper
    if (heapDumpFile == null) {
      CanaryLog.d("Failed to dump heap, will retry in %d ms", WAIT_AFTER_DUMP_FAILED_MILLIS)
      scheduleRetainedInstanceCheck("failed to dump heap", WAIT_AFTER_DUMP_FAILED_MILLIS)
      showRetainedCountWithHeapDumpFailed(retainedKeys.size)
      return
    }

    refWatcher.removeRetainedKeys(retainedKeys) // 移除已經 heap dump 的 retainedKeys

    HeapAnalyzerService.runAnalysis(application, heapDumpFile) // 分析 heap dump 文件
  }