源码阅读 LeakCanary

LeakCanary源码分析

LeakCanary作为常用的内存泄漏分析工具，那是如何检测内存泄漏的呢？从注册入口分析，最新的LeakCanary 2.14，通过ContentProvider自动获取Context完成注册。

<providerandroid:name="leakcanary.internal.MainProcessAppWatcherInstaller"android:authorities="${applicationId}.leakcanary-installer"android:enabled="@bool/leak_canary_watcher_auto_install"android:exported="false" />

一、MainProcessAppWatcherInstaller

leakcanary.internal.MainProcessAppWatcherInstaller 的 onCreate：

internal class MainProcessAppWatcherInstaller : ContentProvider() {override fun onCreate(): Boolean {val application = context!!.applicationContext as ApplicationAppWatcher.manualInstall(application)return true}...
}

二、AppWatcher.manualInstall

manualInstall 中 完成 安装：

// leakcanary.internal.InternalLeakCanary 内部实现
LeakCanaryDelegate.loadLeakCanary(application)// 相关 Activity/Fragment 组件的 检测类，都初始化
watchersToInstall.forEach {it.install()
}

2.1 appDefaultWatchers

watchersToInstall 默认由 AppWatcher.appDefaultWatchers 创建 组件的内存检查对象。
他们都实现 InstallableWatcher 接口，实现 install() 和 uninstall() 方法。

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

2.2 ActivityWatcher - Activity的泄漏分析

Activity 利用生命周期函数 检测。

1. 利用 Application.registerActivityLifecycleCallbacks() 监听
2. onActivityDestroyed()时，调用 objectWatcher.expectWeaklyReachable() 进行 弱可达性分析。

三、ObjectWatcher

ObjectWatcher 完成 内存检查对象的 弱引用创建 和 GC处理。
所有 Activity Fragment View 检测的 InstallableWatcher 都有 objectWatcher 成员，
需要检查泄漏时，来调用 expectWeaklyReachable 方法。

3.1 AppWatcher.objectWatcher 创建默认值

  val objectWatcher = ObjectWatcher(clock = { SystemClock.uptimeMillis() },checkRetainedExecutor = {check(isInstalled) {"AppWatcher not installed"}mainHandler.postDelayed(it, retainedDelayMillis)},isEnabled = { true })

解释： checkRetainedExecutor 作为 Executor 实现，延迟 5s 在 mainHandler 主线程完成。

3.2 expectWeaklyReachable 检查方法

• KeyedWeakReference
• watchedObjects[key]

  @Synchronized override fun expectWeaklyReachable(watchedObject: Any,description: String) {if (!isEnabled()) {return}removeWeaklyReachableObjects()val key = UUID.randomUUID().toString()val watchUptimeMillis = clock.uptimeMillis()val reference =KeyedWeakReference(watchedObject, key, description, watchUptimeMillis, queue)SharkLog.d {"Watching " +(if (watchedObject is Class<*>) watchedObject.toString() else "instance of ${watchedObject.javaClass.name}") +(if (description.isNotEmpty()) " ($description)" else "") +" with key $key"}watchedObjects[key] = referencecheckRetainedExecutor.execute {moveToRetained(key)}}

相关字段说明：

1. KeyedWeakReference 继承自 WeakReference，增加了 key 用于判断。
2. watchedObjects 保存 UUID 为key的弱引用对象
3. queue 为 ReferenceQueue, 用于GC回收时，弱引用会自动进入队列，也就是 未泄漏。
4. checkRetainedExecutor 是 Executor，默认实现 延迟5s 执行。

3.3 removeWeaklyReachableObjects

queue中是 准备被回收的 Reference。
循环 queue.poll() 获取，并移除 要回收 的引用对象。

  private fun removeWeaklyReachableObjects() {var ref: KeyedWeakReference?do {ref = queue.poll() as KeyedWeakReference?if (ref != null) {watchedObjects.remove(ref.key)}} while (ref != null)}

3.4 moveToRetained

这里会 触发 InternalLeakCanary 的 onObjectRetainer()，进一步 处理。

  @Synchronized private fun moveToRetained(key: String) {removeWeaklyReachableObjects()val retainedRef = watchedObjects[key]if (retainedRef != null) {retainedRef.retainedUptimeMillis = clock.uptimeMillis()onObjectRetainedListeners.forEach { it.onObjectRetained() }}}

四、InternalLeakCanary

回到 AppWatcher.manualInstall() 方法，对应：

LeakCanaryDelegate.loadLeakCanary(application)

会通过反射 创建 InternalLeakCanary对象， 并执行 InternalLeakCanary.invoke 方法，注册了上面的OnObjectRetainedListener监听器：

AppWatcher.objectWatcher.addOnObjectRetainedListener(this)

4.1 onObjectRetained

–> scheduleRetainedObjectCheck()
–> heapDumpTrigger.scheduleRetainedObjectCheck()
–> heapDumpTrigger.checkRetainedObjects()

checkRetainedObjects() 源码：

    ...var retainedReferenceCount = objectWatcher.retainedObjectCountif (retainedReferenceCount > 0) {gcTrigger.runGc()retainedReferenceCount = objectWatcher.retainedObjectCount}...dumpHeap(retainedReferenceCount = retainedReferenceCount,retry = true,reason = "$retainedReferenceCount retained objects, app is $visibility")

这里关键地方：

1. gcTrigger.runGc() 运行GC，检测泄漏对象数量。
2. heapDump() 方法，保存栈信息，本质是 Android的 Debug.dumpHprofData()

看源码：HeapDumpTrigger.kt

4.2 GcTrigger

通过 Runtime.getRuntime().gc() 进行 GC 操作。

  object Default : GcTrigger {override fun runGc() {Runtime.getRuntime().gc()enqueueReferences()System.runFinalization()}...}

源码：GcTrigger.kt

4.3 AndroidDebugHeapDumper

利用 Android Api Debug.dumpHprofData(path) 获取栈信息：

object AndroidDebugHeapDumper : HeapDumper {override fun dumpHeap(heapDumpFile: File) {Debug.dumpHprofData(heapDumpFile.absolutePath)}
}

文档

• LeakCanary v2.14 | Github
• LeakCanary Getting Started
• 探索Android开源框架 - 7. LeakCanary使用及源码解析
• LeakCanary2.6抽丝剥茧-源码分析
• LeakCanary2源码解析