LeakCanary简单分析

在使用LeakCanary的时候要引入：

debugImplementation 'com.squareup.leakcanary:leakcanary-android:2.4'

debugImplementation ： debugImplementation 只在debug模式的编译和最终的debug apk打包时有效

LeakCanary的初始化是利用ContentProvider进行初始化的，

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

ContentProvider是在Application的onCreate的前面执行的，也就是在App启动的时候已经初始化好了。具体的ContentProvider是在什么时候执行的可以参考博客。

下面是AppWatcherInstaller的ContentProvider的onCreate代码：

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

AppWatcher是一个单例类只要作用：

The entry point API for using [ObjectWatcher] in an Android app. [AppWatcher.objectWatcher] is
* in charge of detecting retained objects, and [AppWatcher] is auto configured on app start to
* pass it activity and fragment instances. Call [ObjectWatcher.watch] on [objectWatcher] to
* watch any other object that you expect to be unreachable.

在Android应用中使用[ObjectWatcher]的入口点API。 *[AppWatcher.objectWatcher]负责检测保留的对象，[AppWatcher]在应用程序启动时自动配置为通过它的Activity和Fragment实例。

调用[objectWatcher]上的[ObjectWatcher.watch]以监视您期望无法访问的任何其他对象。

  /*** [AppWatcher] is automatically installed in the main process on startup. You can* disable this behavior by overriding the `leak_canary_watcher_auto_install` boolean resource:** ```* <?xml version="1.0" encoding="utf-8"?>* <resources>*   <bool name="leak_canary_watcher_auto_install">false</bool>* </resources>* ```** If you disabled automatic install then you can call this method to install [AppWatcher].*/fun manualInstall(application: Application) {InternalAppWatcher.install(application)}这是在values.xml中的一个字段
<?xml version="1.0" encoding="utf-8"?>
<resources><bool name="leak_canary_watcher_auto_install">true</bool>
</resources>

下面就是install的代码：

 fun install(application: Application) {checkMainThread()//检查是否在主线程，如果不是抛出异常if (this::application.isInitialized) {//判断这个lateinit的属性是否被复制return}SharkLog.logger = DefaultCanaryLog()//设置日志打印InternalAppWatcher.application = applicationval configProvider = { AppWatcher.config }//设置config//下面这两个就是观察Activity和Fragment是否泄漏的ActivityDestroyWatcher.install(application, objectWatcher, configProvider)FragmentDestroyWatcher.install(application, objectWatcher, configProvider)onAppWatcherInstalled(application)}

data class Config(/*** Whether AppWatcher should automatically watch destroyed activity instances.** Defaults to true.*/val watchActivities: Boolean = true,/*** Whether AppWatcher should automatically watch destroyed fragment instances.** Defaults to true.*/val watchFragments: Boolean = true,/*** Whether AppWatcher should automatically watch destroyed fragment view instances.** Defaults to true.*/val watchFragmentViews: Boolean = true,/*** Whether AppWatcher should automatically watch cleared [androidx.lifecycle.ViewModel]* instances.** Defaults to true.*/val watchViewModels: Boolean = true,/*** How long to wait before reporting a watched object as retained.** Default to 5 seconds.*/val watchDurationMillis: Long = TimeUnit.SECONDS.toMillis(5),/*** Deprecated, this didn't need to be a part of the API.* Used to indicate whether AppWatcher should watch objects (by keeping weak references to* them). Currently a no-op.** If you do need to stop watching objects, simply don't pass them to [objectWatcher].*/@Deprecated("This didn't need to be a part of LeakCanary's API. No-Op.")val enabled: Boolean = true)

下面我们先分析这个Activity的写泄漏：主要是给application的registerActivityLifecycleCallbacks添加一个监听，

internal class ActivityDestroyWatcher private constructor(private val objectWatcher: ObjectWatcher,private val configProvider: () -> Config
) {private val lifecycleCallbacks =object : Application.ActivityLifecycleCallbacks by noOpDelegate() {override fun onActivityDestroyed(activity: Activity) {if (configProvider().watchActivities) {objectWatcher.watch(activity, "${activity::class.java.name} received Activity#onDestroy() callback")}}}companion object {fun install(application: Application,objectWatcher: ObjectWatcher,configProvider: () -> Config) {val activityDestroyWatcher =ActivityDestroyWatcher(objectWatcher, configProvider)application.registerActivityLifecycleCallbacks(activityDestroyWatcher.lifecycleCallbacks)}}
}

下面就是在回调了Activity的onDestroy的方法后执行的内容：这个地方就是创建一个弱引用对象，进行观察，当执行完GC之后是否还存在，判断是否泄漏

/*** Watches the provided [watchedObject].** @param description Describes why the object is watched.*/@Synchronized fun watch(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)}}

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

这个地方的onObjectRetained()方法是InternalLeakCanary中的onObjectRetained()方法可以看到调用的时候HeapDumpTrigger对象的onObjectRetained()方法下面看下这个方法

fun onObjectRetained() {scheduleRetainedObjectCheck(reason = "found new object retained",rescheduling = false)}private fun checkRetainedObjects(reason: String) {val config = configProvider()// A tick will be rescheduled when this is turned back on.if (!config.dumpHeap) {SharkLog.d { "Ignoring check for retained objects scheduled because $reason: LeakCanary.Config.dumpHeap is false" }return}//弱引用对象中保存的没有回收的Activity的数量var retainedReferenceCount = objectWatcher.retainedObjectCountif (retainedReferenceCount > 0) {//数量大于0执行GC，执行GC后再获取一次个数gcTrigger.runGc()retainedReferenceCount = objectWatcher.retainedObjectCount}//这个地方是检查回收对象的数量是否超过定义的阀值(5)如果没有就直接返回if (checkRetainedCount(retainedReferenceCount, config.retainedVisibleThreshold)) return//判断是否连接了调试解调器，如果是就直接返回if (!config.dumpHeapWhenDebugging && DebuggerControl.isDebuggerAttached) {onRetainInstanceListener.onEvent(DebuggerIsAttached)showRetainedCountNotification(objectCount = retainedReferenceCount,contentText = application.getString(R.string.leak_canary_notification_retained_debugger_attached))scheduleRetainedObjectCheck(reason = "debugger is attached",rescheduling = true,delayMillis = WAIT_FOR_DEBUG_MILLIS)return}val now = SystemClock.uptimeMillis()val elapsedSinceLastDumpMillis = now - lastHeapDumpUptimeMillis//如果时间小于预定义的5秒就Notification并且返回if (elapsedSinceLastDumpMillis < WAIT_BETWEEN_HEAP_DUMPS_MILLIS) {onRetainInstanceListener.onEvent(DumpHappenedRecently)showRetainedCountNotification(objectCount = retainedReferenceCount,contentText = application.getString(R.string.leak_canary_notification_retained_dump_wait))scheduleRetainedObjectCheck(reason = "previous heap dump was ${elapsedSinceLastDumpMillis}ms ago (< ${WAIT_BETWEEN_HEAP_DUMPS_MILLIS}ms)",rescheduling = true,delayMillis = WAIT_BETWEEN_HEAP_DUMPS_MILLIS - elapsedSinceLastDumpMillis)return}SharkLog.d { "Check for retained objects found $retainedReferenceCount objects, dumping the heap" }dismissRetainedCountNotification()//把堆中的信息保存到文件dumpHeap(retainedReferenceCount, retry = true)}

private fun dumpHeap(retainedReferenceCount: Int,retry: Boolean) {saveResourceIdNamesToMemory()val heapDumpUptimeMillis = SystemClock.uptimeMillis()KeyedWeakReference.heapDumpUptimeMillis = heapDumpUptimeMillisval heapDumpFile = heapDumper.dumpHeap()if (heapDumpFile == null) {if (retry) {SharkLog.d { "Failed to dump heap, will retry in $WAIT_AFTER_DUMP_FAILED_MILLIS ms" }scheduleRetainedObjectCheck(reason = "failed to dump heap",rescheduling = true,delayMillis = WAIT_AFTER_DUMP_FAILED_MILLIS)} else {SharkLog.d { "Failed to dump heap, will not automatically retry" }}showRetainedCountNotification(objectCount = retainedReferenceCount,contentText = application.getString(R.string.leak_canary_notification_retained_dump_failed))return}lastDisplayedRetainedObjectCount = 0lastHeapDumpUptimeMillis = SystemClock.uptimeMillis()objectWatcher.clearObjectsWatchedBefore(heapDumpUptimeMillis)//保存到文件后分析这个hprof文件HeapAnalyzerService.runAnalysis(application, heapDumpFile)}

fun runAnalysis(context: Context,heapDumpFile: File) {//启动一个前台服务分析堆文件val intent = Intent(context, HeapAnalyzerService::class.java)intent.putExtra(HEAPDUMP_FILE_EXTRA, heapDumpFile)startForegroundService(context, intent)}

下面就是hprof文件的分析了，LeakCanary用的Shark进行分析的。shark官网

LeakCanary的官网。

LeakCanary自动检测以下对象的泄漏：

销毁Activity实例
销毁Fragment实例
destroy fragment View实例
清除ViewModel实例

它就会通过4个步骤自动检测并报告内存泄漏：

检测保留的对象。
转储堆。
分析堆。
分类泄漏。

详细的流程可以去官网看下，地址为https://square.github.io/leakcanary/fundamentals-how-leakcanary-works/

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