Android内存泄露检测 LeakCanary2.0(Kotlin版)的实现原理

dependencies {
  // debugImplementation because LeakCanary should only run in debug builds.
  debugImplementation 'com.squareup.leakcanary:leakcanary-android:2.5'
}

internal sealed class AppWatcherInstaller : ContentProvider() {
 
  /**
   * [MainProcess] automatically sets up the LeakCanary code that runs in the main app process.
   */
  internal class MainProcess : AppWatcherInstaller()
 
  /**
   * When using the `leakcanary-android-process` artifact instead of `leakcanary-android`,
   * [LeakCanaryProcess] automatically sets up the LeakCanary code
   */
  internal class LeakCanaryProcess : AppWatcherInstaller()
 
  override fun onCreate(): Boolean {
    val application = context!!.applicationContext as Application
    AppWatcher.manualInstall(application)
    return true
  }
  //....
}

AppWatcher.objectWatcher.watch(myDetachedView, "View was detached")

//InternalAppWatcher初始化
fun install(application: Application) {
     
    ......
     
    val configProvider = { AppWatcher.config }
    ActivityDestroyWatcher.install(application, objectWatcher, configProvider)
    FragmentDestroyWatcher.install(application, objectWatcher, configProvider)
    onAppWatcherInstalled(application)
  }
 
//InternalleakCanary初始化
override fun invoke(application: Application) {
    _application = application
    checkRunningInDebuggableBuild()
 
    AppWatcher.objectWatcher.addOnObjectRetainedListener(this)
 
    val heapDumper = AndroidHeapDumper(application, createLeakDirectoryProvider(application))
 
    val gcTrigger = GcTrigger.Default
 
    val configProvider = { LeakCanary.config }
    //异步线程执行耗时操作
    val handlerThread = HandlerThread(LEAK_CANARY_THREAD_NAME)
    handlerThread.start()
    val backgroundHandler = Handler(handlerThread.looper)
 
    heapDumpTrigger = HeapDumpTrigger(
        application, backgroundHandler, AppWatcher.objectWatcher, gcTrigger, heapDumper,
        configProvider
    )
    //Application 可见性监听
    application.registerVisibilityListener { applicationVisible ->
      this.applicationVisible = applicationVisible
      heapDumpTrigger.onApplicationVisibilityChanged(applicationVisible)
    }
    registerResumedActivityListener(application)
    addDynamicShortcut(application)
 
    disableDumpHeapInTests()
  }

@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] = reference
    checkRetainedExecutor.execute {
      moveToRetained(key)
    }
  }

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
    }
 
    //第一次移除不可达对象
    var retainedReferenceCount = objectWatcher.retainedObjectCount
 
    if (retainedReferenceCount > 0) {
        //主动出发GC
      gcTrigger.runGc()
        //第二次移除不可达对象
      retainedReferenceCount = objectWatcher.retainedObjectCount
    }
 
    //判断是否还有剩余的监听对象存活，且存活的个数是否超过阈值
    if (checkRetainedCount(retainedReferenceCount, config.retainedVisibleThreshold)) return
 
    ....
 
    SharkLog.d { "Check for retained objects found $retainedReferenceCount objects, dumping the heap" }
    dismissRetainedCountNotification()
    dumpHeap(retainedReferenceCount, retry = true)
  }

//HeapDumpTrigger
private fun dumpHeap(
    retainedReferenceCount: Int,
    retry: Boolean
  ) {
      
   ....
      
    HeapAnalyzerService.runAnalysis(application, heapDumpFile)
  }

//HeapAnalyzerService
private fun analyzeHeap(
    heapDumpFile: File,
    config: Config
  ): HeapAnalysis {
    val heapAnalyzer = HeapAnalyzer(this)
 
    val proguardMappingReader = try {
        //解析混淆文件
      ProguardMappingReader(assets.open(PROGUARD_MAPPING_FILE_NAME))
    } catch (e: IOException) {
      null
    }
    //分析hprof文件
    return heapAnalyzer.analyze(
        heapDumpFile = heapDumpFile,
        leakingObjectFinder = config.leakingObjectFinder,
        referenceMatchers = config.referenceMatchers,
        computeRetainedHeapSize = config.computeRetainedHeapSize,
        objectInspectors = config.objectInspectors,
        metadataExtractor = config.metadataExtractor,
        proguardMapping = proguardMappingReader?.readProguardMapping()
    )
  }

fun analyze(
   heapDumpFile: File,
   leakingObjectFinder: LeakingObjectFinder,
   referenceMatchers: List<ReferenceMatcher> = emptyList(),
   computeRetainedHeapSize: Boolean = false,
   objectInspectors: List<ObjectInspector> = emptyList(),
   metadataExtractor: MetadataExtractor = MetadataExtractor.NO_OP,
   proguardMapping: ProguardMapping? = null
 ): HeapAnalysis {
   val analysisStartNanoTime = System.nanoTime()
 
   if (!heapDumpFile.exists()) {
     val exception = IllegalArgumentException("File does not exist: $heapDumpFile")
     return HeapAnalysisFailure(
         heapDumpFile, System.currentTimeMillis(), since(analysisStartNanoTime),
         HeapAnalysisException(exception)
     )
   }
 
   return try {
     listener.onAnalysisProgress(PARSING_HEAP_DUMP)
     Hprof.open(heapDumpFile)
         .use { hprof ->
           val graph = HprofHeapGraph.indexHprof(hprof, proguardMapping)//建立gragh
           val helpers =
             FindLeakInput(graph, referenceMatchers, computeRetainedHeapSize, objectInspectors)
           helpers.analyzeGraph(//分析graph
               metadataExtractor, leakingObjectFinder, heapDumpFile, analysisStartNanoTime
           )
         }
   } catch (exception: Throwable) {
     HeapAnalysisFailure(
         heapDumpFile, System.currentTimeMillis(), since(analysisStartNanoTime),
         HeapAnalysisException(exception)
     )
   }
 }

interface HeapGraph {
  val identifierByteSize: Int
  /**
   * In memory store that can be used to store objects this [HeapGraph] instance.
   */
  val context: GraphContext
  /**
   * All GC roots which type matches types known to this heap graph and which point to non null
   * references. You can retrieve the object that a GC Root points to by calling [findObjectById]
   * with [GcRoot.id], however you need to first check that [objectExists] returns true because
   * GC roots can point to objects that don't exist in the heap dump.
   */
  val gcRoots: List<GcRoot>
  /**
   * Sequence of all objects in the heap dump.
   *
   * This sequence does not trigger any IO reads.
   */
  val objects: Sequence<HeapObject>  //所有对象的序列，包括类对象、实例对象、对象数组、原始类型数组
 
  val classes: Sequence<HeapClass>   //类对象序列
 
  val instances: Sequence<HeapInstance>   //实例对象数组
 
  val objectArrays: Sequence<HeapObjectArray>  //对象数组序列
   
  val primitiveArrays: Sequence<HeapPrimitiveArray>   //原始类型数组序列
}

//PathFinder
private fun State.findPathsFromGcRoots(): PathFindingResults {
    enqueueGcRoots()//1
 
    val shortestPathsToLeakingObjects = mutableListOf<ReferencePathNode>()
    visitingQueue@ while (queuesNotEmpty) {
      val node = poll()//2
 
      if (checkSeen(node)) {//2
        throw IllegalStateException(
            "Node $node objectId=${node.objectId} should not be enqueued when already visited or enqueued"
        )
      }
 
      if (node.objectId in leakingObjectIds) {//3
        shortestPathsToLeakingObjects.add(node)
        // Found all refs, stop searching (unless computing retained size)
        if (shortestPathsToLeakingObjects.size == leakingObjectIds.size) {//4
          if (computeRetainedHeapSize) {
            listener.onAnalysisProgress(FINDING_DOMINATORS)
          } else {
            break@visitingQueue
          }
        }
      }
 
      when (val heapObject = graph.findObjectById(node.objectId)) {//5
        is HeapClass -> visitClassRecord(heapObject, node)
        is HeapInstance -> visitInstance(heapObject, node)
        is HeapObjectArray -> visitObjectArray(heapObject, node)
      }
    }
    return PathFindingResults(shortestPathsToLeakingObjects, dominatedObjectIds)
  }