Android LeakCanary的使用方法介绍

目录

• 1.LeakCanary 如何自动初始化
• 2.LeakCanary如何检测内存泄漏
• 2.1LeakCanary初始化时做了什么
• 2.2LeakCanary如何触发检测
• 2.3LeakCanary如何检测泄漏的对象
• 2.4弱引用 WeakReference

1.LeakCanary 如何自动初始化

LeakCanary只需添加依赖就可以实现自动初始化。LeakCanary是通过ContentProvider实现初始化的，在ContentProvider 的 onCreate方法中初始化LeakCanary。并且MainProcessAppWatcherInstaller是在主线程中初始化的。注意：ContentProvider的初始化是在Application的onCreate之前完成的，所以LeakCanary的初始化方法AppWatcher.manualInstall(application)也是在Application的onCreate之前完成的。

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

2.LeakCanary如何检测内存泄漏

2.1LeakCanary初始化时做了什么

AppWatcher.kt

@JvmOverloads
fun manualInstall(
  application: Application,
  retainedDelayMillis: Long = TimeUnit.SECONDS.toMillis(5),
  watchersToInstall: List<InstallableWatcher> = appDefaultWatchers(application)
) {
  checkMainThread()
  if (isInstalled) {
    throw IllegalStateException(
      "AppWatcher already installed, see exception cause for prior install call", installCause
    )
  }
  check(retainedDelayMillis >= 0) {
    "retainedDelayMillis $retainedDelayMillis must be at least 0 ms"
  }
  installCause = RuntimeException("manualInstall() first called here")
  this.retainedDelayMillis = retainedDelayMillis
  if (application.isDebuggableBuild) {
    LogcatSharkLog.install()
  }
  // Requires AppWatcher.objectWatcher to be set
  LeakCanaryDelegate.loadLeakCanary(application)
  watchersToInstall.forEach {
    it.install()
  }
}

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

在appDefaultWatchers方法中，会默认初始化一些Watcher，在默认情况下，我们只会监控Activity,Fragment,RootView,Service这些对象是否泄漏。

2.2LeakCanary如何触发检测

以ActivityWatcher为例:

/**
 * Expects activities to become weakly reachable soon after they receive the [Activity.onDestroy]
 * callback.
 */
class ActivityWatcher(
  private val application: Application,
  private val reachabilityWatcher: ReachabilityWatcher
) : InstallableWatcher {
  private val lifecycleCallbacks =
    object : Application.ActivityLifecycleCallbacks by noOpDelegate() {
      override fun onActivityDestroyed(activity: Activity) {
        reachabilityWatcher.expectWeaklyReachable(
          activity, "${activity::class.java.name} received Activity#onDestroy() callback"
        )
      }
    }
  override fun install() {
    application.registerActivityLifecycleCallbacks(lifecycleCallbacks)
  }
  override fun uninstall() {
    application.unregisterActivityLifecycleCallbacks(lifecycleCallbacks)
  }
}

在Activity.onDestory时，就会触发检测内存泄漏。通过ActivityLifecycleCallbacks监听生命周期变化，在onActivityDestroyed方法中调用ReachabilityWatcher的expectWeaklyReachable方法。

2.3LeakCanary如何检测泄漏的对象

以Activity为例，通过ReachabilityWatcher的expectWeaklyReachable方法检测。

fun interface ReachabilityWatcher {
  /**
   * Expects the provided [watchedObject] to become weakly reachable soon. If not,
   * [watchedObject] will be considered retained.
   */
  fun expectWeaklyReachable(
    watchedObject: Any,
    description: String
  )
}

ObjectWatcher.kt

ObjectWatcher实现ReachabilityWatcher接口。

private val watchedObjects = mutableMapOf()

private val queue = ReferenceQueue()

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

1.通过观察的实例watchedObject构建弱引用KeyedWeakReference实例，watchedObject与ReferenceQueue关联，当对象被回收时，该弱引用对象将被存入ReferenceQueue当中。

2.弱引用KeyedWeakReference实例会被被存储在watchedObjects中（Map）。

3.检测过程中，会调用removeWeaklyReachableObjects,将已回收对象从watchedObjects中移除。

4.如果watchedObjects中没有移除对象，证明它没有被回收，那么就会调用moveToRetained。

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

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

2.4弱引用 WeakReference

只要 GC 发现一个对象只有弱引用，则就会回收此弱引用对象。

public class WeakReference<T> extends Reference<T> {
    public WeakReference(T referent) {
        super(referent);
    }
    public WeakReference(T referent, ReferenceQueue<? super T> q) {
        super(referent, q);
    }
}

var str: Any? = Any()
val quque = ReferenceQueue<Any>()
val weakReference = WeakReference<Any>(str, quque)
val weakReference_before_gc = weakReference.get()
Log.v("reference_tag", weakReference_before_gc.toString())
str = null
System.gc()
Handler().postDelayed( {
    val weakReference_after_gc = weakReference.get()
    Log.v("reference_tag", weakReference_after_gc.toString())
}, 2000)

2022-02-27 17:43:04.181 16634-16634/com.example.myapplication V/reference_tag: java.lang.Object@c87946a
2022-02-27 17:43:06.182 16634-16634/com.example.myapplication V/reference_tag: null

到此这篇关于Android LeakCanary的使用方法介绍的文章就介绍到这了,更多相关Android LeakCanary内容请搜索我们以前的文章或继续浏览下面的相关文章希望大家以后多多支持我们！