开源库路径https://github.com/square/leakcanary
源码结构
image
- leakcanary-watcher: 这是一个通用的内存检测器，对外提供一个 RefWatcher#watch(Object watchedReference),它不仅能够检测Activity，还能监测任意常规的 Java Object 的泄漏情况。
- leakcanary-android: 这个 module 是与 Android 的接入点，用来专门监测 Activity 的泄漏情况，内部使用了 application#registerActivityLifecycleCallbacks 方法来监听 onDestory 事件，然后利用 leakcanary-watcher 来进行弱引用＋手动 GC 机制进行监控。
- leakcanary-analyzer: 这个 module 提供了 HeapAnalyzer，用来对 dump 出来的内存进行分析并返回内存分析结果AnalysisResult，内部包含了泄漏发生的路径等信息供开发者寻找定位。
- leakcanary-android-no-op: 这个 module 是专门给 release 的版本用的，内部只提供了两个完全空白的类 LeakCanary 和 RefWatcher，这两个类不会做任何内存泄漏相关的分析。因为 LeakCanary 本身会由于不断 gc 影响到 app 本身的运行，而且主要用于开发阶段的内存泄漏检测。因此对于 release 则可以 disable 所有泄漏分析。
原理简介
LeakCanary的原理非常简单。正常情况下一个Activity在执行Destroy之后就要销毁，LeakCanary做的就是在一个Activity/Fragment Destroy之后将它放在一个WeakReference中，然后将这个WeakReference关联到一个ReferenceQueue，查看ReferenceQueue是否存在Activity的引用，如果不在这个队列中，执行一些GC清洗操作，再次查看。如果不存在则证明该Activity/Fragment泄漏了，之后Dump出heap信息，并用haha这个开源库去分析泄漏路径。
基本原理图示
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源码分析
简单分析，只分析如何实现内存泄漏检测的基本思路
第一步:入口函数分析LeakCanary.install(Application application)
集成使用LeakCanary基本上是在Application onCreate中调用即可LeakCanary.install(this);
，这是总的入口函数，第一步分析就从这里开始。
/**
* Creates a {@link RefWatcher} that works out of the box, and starts watching activity
* references (on ICS+).
*/
public static @NonNull RefWatcher install(@NonNull Application application) {
//返回的是AndroidRefWatcherBuilder继承自RefWatcher对象
return refWatcher(application).listenerServiceClass(DisplayLeakService.class)
.excludedRefs(AndroidExcludedRefs.createAppDefaults().build())
.buildAndInstall();
}
分析一:返回AndroidRefWatcherBuilder对象
refWatcher(application)
分析二:调用返回AndroidRefWatcherBuilder.buildAndInstall
buildAndInstall
分析一: refWatcher(application)
该方法调用的refWatcher返回了AndroidRefWatcherBuilder对象：
public static @NonNull AndroidRefWatcherBuilder refWatcher(@NonNull Context context) {
return new AndroidRefWatcherBuilder(context);
}
分析二:AndroidRefWatcherBuilder.buildAndInstall
进行设置监控所需要的相关系统lifeCycle回调，包含ActivityLifecycleCallbacks以及FragmentLifecycleCallbacks。
/**
* Creates a {@link RefWatcher} instance and makes it available through {@link
* LeakCanary#installedRefWatcher()}.
*
* Also starts watching activity references if {@link #watchActivities(boolean)} was set to true.
*
* @throws UnsupportedOperationException if called more than once per Android process.
*/
public @NonNull RefWatcher buildAndInstall() {
//buildAndInstall只允许调用一次
if (LeakCanaryInternals.installedRefWatcher != null) {
throw new UnsupportedOperationException("buildAndInstall() should only be called once.");
}
//创建用于实际处理判断内存泄漏的监控对象RefWatcher,放在内容第二步分析
RefWatcher refWatcher = build();
if (refWatcher != DISABLED) {
LeakCanaryInternals.setEnabledAsync(context, DisplayLeakActivity.class, true);
if (watchActivities) {
//watchActivities默认为true,开始activity引用的监控
ActivityRefWatcher.install(context, refWatcher);
}
if (watchFragments) {
//watchFragments默认为true,开始fragment引用的监控
FragmentRefWatcher.Helper.install(context, refWatcher);
}
}
//赋值installedRefWatcher，用于判断已创建成功
LeakCanaryInternals.installedRefWatcher = refWatcher;
return refWatcher;
}
分析三：设置activity资源泄漏监控:
ActivityRefWatcher.install
分析四：设置Fragment资源泄漏监控：
FragmentRefWatcher.Helper.install
分析三:ActivityRefWatcher.install
这边主要是对app注册了个ActivityLifecycleCallbacks，在每次activity被销毁后都会回调到onActivityDestroyed，在onActivityDestroyed中获取在理论上即将被销毁的activity对象，调用refWatcher.watch检测其是否发生泄漏
public static void install(@NonNull Context context, @NonNull RefWatcher refWatcher) {
Application application = (Application) context.getApplicationContext();
ActivityRefWatcher activityRefWatcher = new ActivityRefWatcher(application, refWatcher);
//注册个lifecycleCallbacks，在里面分析activity的内存泄漏问题
application.registerActivityLifecycleCallbacks(activityRefWatcher.lifecycleCallbacks);
}
//app所有activity生命周期结束自动回调
private final Application.ActivityLifecycleCallbacks lifecycleCallbacks =
new ActivityLifecycleCallbacksAdapter() {
@Override public void onActivityDestroyed(Activity activity) {
//调用的还是refWatcher操作，ActivityRefWatcher只是为了activity周期监听
refWatcher.watch(activity);
}
};
下文第二步分析activity是否存在内存泄漏:
refWatcher.watch(activity)
分析四:FragmentRefWatcher.Helper.install
这边主要用于ActivityLifecycleCallbacks中各个activity创建的时候,
获取到activity对应的FragmentManager注册FragmentLifecycleCallbacks.后续当有Fragment消耗触发onFragmentViewDestroyed或者onFragmentDestroyed时，则获取理论上即将被销毁的view/fragment对象，调用refWatcher.watch检测其是否发生泄漏。
public static void install(Context context, RefWatcher refWatcher) {
List<FragmentRefWatcher> fragmentRefWatchers = new ArrayList<>();
if (SDK_INT >= O) {
//添加了个AndroidOFragmentRefWatcher用于对android.app.FragmentManager设置FragmentLifecycleCallbacks
fragmentRefWatchers.add(new AndroidOFragmentRefWatcher(refWatcher));
}
try {
//反射添加SupportFragmentRefWatcher用于对android.support.v4.app.FragmentManager设置FragmentLifecycleCallbacks
Class<?> fragmentRefWatcherClass = Class.forName(SUPPORT_FRAGMENT_REF_WATCHER_CLASS_NAME);
Constructor<?> constructor =
fragmentRefWatcherClass.getDeclaredConstructor(RefWatcher.class);
FragmentRefWatcher supportFragmentRefWatcher =
(FragmentRefWatcher) constructor.newInstance(refWatcher);
fragmentRefWatchers.add(supportFragmentRefWatcher);
} catch (Exception ignored) {
ignored.printStackTrace();
}
if (fragmentRefWatchers.size() == 0) {
return;
}
Helper helper = new Helper(fragmentRefWatchers);
//这边再次注册了另外一个ActivityLifecycleCallbacks
Application application = (Application) context.getApplicationContext();
application.registerActivityLifecycleCallbacks(helper.activityLifecycleCallbacks);
}
//该ActivityLifecycleCallbacks主要在onActivityCreated回调的时候执行上面添加的FragmentRefWatcher.watchFragments方法
private final Application.ActivityLifecycleCallbacks activityLifecycleCallbacks =
new ActivityLifecycleCallbacksAdapter() {
@Override public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
for (FragmentRefWatcher watcher : fragmentRefWatchers) {
watcher.watchFragments(activity);
}
}
};
分析五:fragmentRefWatchers.add(new AndroidOFragmentRefWatcher(refWatcher)):
用于对android.app.FragmentManager设置FragmentLifecycleCallbacks
分析六:fragmentRefWatchers.add(supportFragmentRefWatcher):
用于对android.support.v4.app.FragmentManager设置FragmentLifecycleCallbacks
分析五:fragmentRefWatchers.add(new AndroidOFragmentRefWatcher(refWatcher)):
添加了个AndroidOFragmentRefWatcher用于对android.app.FragmentManager设置FragmentLifecycleCallbacks,后续在fragment生命周期结束时获取并判断是否存在fragment内存泄漏。
AndroidOFragmentRefWatcher.watchFragments:
private final FragmentManager.FragmentLifecycleCallbacks fragmentLifecycleCallbacks =
new FragmentManager.FragmentLifecycleCallbacks() {
@Override public void onFragmentViewDestroyed(FragmentManager fm, Fragment fragment) {
//检测即将被回收的view是否存在泄漏
View view = fragment.getView();
if (view != null) {
refWatcher.watch(view);
}
}
@Override
public void onFragmentDestroyed(FragmentManager fm, Fragment fragment) {
//检测即将被回收的fragment是否存在泄漏
refWatcher.watch(fragment);
}
};
@Override public void watchFragments(Activity activity) {
FragmentManager fragmentManager = activity.getFragmentManager();
//对activity注册FragmentLifecycleCallbacks生命周期监听
fragmentManager.registerFragmentLifecycleCallbacks(fragmentLifecycleCallbacks, true);
}
分析六:fragmentRefWatchers.add(supportFragmentRefWatcher)：
添加了个SupportFragmentRefWatcher用于对android.support.v4.app.FragmentManager设置FragmentLifecycleCallbacks,后续在fragment生命周期结束时获取并判断是否存在fragment内存泄漏。
SupportFragmentRefWatcher.watchFragments:
private final FragmentManager.FragmentLifecycleCallbacks fragmentLifecycleCallbacks =
new FragmentManager.FragmentLifecycleCallbacks() {
@Override public void onFragmentViewDestroyed(FragmentManager fm, Fragment fragment) {
//检测即将被回收的view是否存在泄漏
View view = fragment.getView();
if (view != null) {
refWatcher.watch(view);
}
}
@Override public void onFragmentDestroyed(FragmentManager fm, Fragment fragment) {
//检测即将被回收的fragment是否存在泄漏
refWatcher.watch(fragment);
}
};
@Override public void watchFragments(Activity activity) {
if (activity instanceof FragmentActivity) {
//对activity注册FragmentLifecycleCallbacks生命周期监听
FragmentManager supportFragmentManager =
((FragmentActivity) activity).getSupportFragmentManager();
supportFragmentManager.registerFragmentLifecycleCallbacks(fragmentLifecycleCallbacks, true);
}
}
第二步:内存是否泄漏判断refWatcher.watch()
首先从RefWatcher对象的创建开始
/** Creates a {@link RefWatcher}. */
public final RefWatcher build() {
if (isDisabled()) {
return RefWatcher.DISABLED;
}
if (heapDumpBuilder.excludedRefs == null) {
heapDumpBuilder.excludedRefs(defaultExcludedRefs());
}
HeapDump.Listener heapDumpListener = this.heapDumpListener;
if (heapDumpListener == null) {
heapDumpListener = defaultHeapDumpListener();
}
//默认为null
DebuggerControl debuggerControl = this.debuggerControl;
if (debuggerControl == null) {
debuggerControl = defaultDebuggerControl();
}
HeapDumper heapDumper = this.heapDumper;
if (heapDumper == null) {
heapDumper = defaultHeapDumper();
}
//设置默认的监控执行处理器defaultWatchExecutor，调用AndroidRefWatcherBuilder.defaultWatchExecutor()获取
WatchExecutor watchExecutor = this.watchExecutor;
if (watchExecutor == null) {
watchExecutor = defaultWatchExecutor();
}
//获取Gc处理器RefWatcherBuilder.defaultGcTrigger()
GcTrigger gcTrigger = this.gcTrigger;
if (gcTrigger == null) {
gcTrigger = defaultGcTrigger();
}
if (heapDumpBuilder.reachabilityInspectorClasses == null) {
heapDumpBuilder.reachabilityInspectorClasses(defaultReachabilityInspectorClasses());
}
//返回内存泄漏监控处理者RefWatcher
return new RefWatcher(watchExecutor, debuggerControl, gcTrigger, heapDumper, heapDumpListener,
heapDumpBuilder);
}
分析七:defaultWatchExecutor();
分析七:defaultWatchExecutor
AndroidWatchExecutor对象的创建:
//默认延时参数5秒
private static final long DEFAULT_WATCH_DELAY_MILLIS = SECONDS.toMillis(5);
@Override protected @NonNull WatchExecutor defaultWatchExecutor() {
return new AndroidWatchExecutor(DEFAULT_WATCH_DELAY_MILLIS);
}
AndroidWatchExecutor实现的功能
AndroidWatchExecutor主要是做了一个简单的延时功能，因为activity、fragment等处罚ondestroy时，这些对象理论上即将被回收，但是还未被回收，所以AndroidWatchExecutor默认将检测任务发送到异步线程中做了个5秒的延时，注意这边是在异步线程，不阻塞主线程。在延时时间到了后，将检测任务再发送回主线程进行检测，注意这边之所以再发送回主线程，是因为gc操作只能在主线程触发。
AndroidWatchExecutor类:
public final class AndroidWatchExecutor implements WatchExecutor {
static final String LEAK_CANARY_THREAD_NAME = "LeakCanary-Heap-Dump";
private final Handler mainHandler;
private final Handler backgroundHandler;
private final long initialDelayMillis;
private final long maxBackoffFactor;
public AndroidWatchExecutor(long initialDelayMillis) {
//创建运行与主线程的mainHandler
mainHandler = new Handler(Looper.getMainLooper());
HandlerThread handlerThread = new HandlerThread(LEAK_CANARY_THREAD_NAME);
handlerThread.start();
//创建运行于后台线程的backgroundHandler
backgroundHandler = new Handler(handlerThread.getLooper());
//默认为5s
this.initialDelayMillis = initialDelayMillis;
maxBackoffFactor = Long.MAX_VALUE / initialDelayMillis;
}
@Override public void execute(@NonNull Retryable retryable) {
if (Looper.getMainLooper().getThread() == Thread.currentThread()) {
//当前是主线程则执行waitForIdle
waitForIdle(retryable, 0);
} else {
//当前是后台线程则执行postWaitForIdle
postWaitForIdle(retryable, 0);
}
}
private void postWaitForIdle(final Retryable retryable, final int failedAttempts) {
//将检测任务Retryable post到主线程中去执行
mainHandler.post(new Runnable() {
@Override public void run() {
waitForIdle(retryable, failedAttempts);
}
});
}
private void waitForIdle(final Retryable retryable, final int failedAttempts) {
// This needs to be called from the main thread.
//当主线程空闲时则执行postToBackgroundWithDelay
Looper.myQueue().addIdleHandler(new MessageQueue.IdleHandler() {
@Override public boolean queueIdle() {
postToBackgroundWithDelay(retryable, failedAttempts);
return false;
}
});
}
private void postToBackgroundWithDelay(final Retryable retryable, final int failedAttempts) {
long exponentialBackoffFactor = (long) Math.min(Math.pow(2, failedAttempts), maxBackoffFactor);
long delayMillis = initialDelayMillis * exponentialBackoffFactor;
//延时5秒执行Retryable检测
backgroundHandler.postDelayed(new Runnable() {
@Override public void run() {
Retryable.Result result = retryable.run();
if (result == RETRY) {
postWaitForIdle(retryable, failedAttempts + 1);
}
}
}, delayMillis);
}
}
判断是否存在内存泄漏调用RefWatcher.watch:
public void watch(Object watchedReference, String referenceName) {
if (this == DISABLED) {
return;
}
checkNotNull(watchedReference, "watchedReference");
checkNotNull(referenceName, "referenceName");
//开始检测的时间
final long watchStartNanoTime = System.nanoTime();
//产生随机的key , 作为需要检测的对象的唯一标识
String key = UUID.randomUUID().toString();
//保存该key
retainedKeys.add(key);
//创建对应的对需要监控的watchedReference对象的弱引用并与ReferenceQueue绑定
final KeyedWeakReference reference =
new KeyedWeakReference(watchedReference, key, referenceName, queue);
//开始确认该对象是否被回收了
ensureGoneAsync(watchStartNanoTime, reference);
}
做了个简单的线程判断ensureGoneAsync
这边看到使用到了上面watchExecutor延时5秒后，再执行ensureGone
private void ensureGoneAsync(final long watchStartNanoTime, final KeyedWeakReference reference) {
watchExecutor.execute(new Retryable() {
@Override public Retryable.Result run() {
return ensureGone(reference, watchStartNanoTime);
}
});
}
确认是否回收ensureGone
该函数执行的一个基本操作就是:
1.首先判断ReferenceQueue是否存在要检测内存泄漏的reference对象，不存在则代表可能发生泄漏
2.主动触发一次gc，进行内存回收
3.再次判断ReferenceQueue是否存在要检测内存泄漏的reference对象，不存在则代表可能发生泄漏
4.若发生泄漏则dump出内存hprof文件，进行分析，从中分析出内存泄漏的路径
Retryable.Result ensureGone(final KeyedWeakReference reference, final long watchStartNanoTime) {
//gc准备开启的时间
long gcStartNanoTime = System.nanoTime();
//开始监控到准备gc的时间，大概5秒多，因为前边延时5秒
long watchDurationMs = NANOSECONDS.toMillis(gcStartNanoTime - watchStartNanoTime);
//移除已经被回收内存的监控对象的Key
removeWeaklyReachableReferences();
if (debuggerControl.isDebuggerAttached()) {
// The debugger can create false leaks.
return RETRY;
}
//判断该reference对象是否被回收了,如果已经被回收，返回DONE，
if (gone(reference)) {
return DONE;
}
//如果尚未被回收，则主动触发一次gc
gcTrigger.runGc();
//移除已经被回收内存的监控对象的Key
removeWeaklyReachableReferences();
//判断该reference对象是否被回收了,如果已经被回收，返回DONE，
if (!gone(reference)) {
//该reference对象尚未被回收
long startDumpHeap = System.nanoTime();
long gcDurationMs = NANOSECONDS.toMillis(startDumpHeap - gcStartNanoTime);
//主动dump出内存Hprof文件
File heapDumpFile = heapDumper.dumpHeap();
if (heapDumpFile == RETRY_LATER) {
// Could not dump the heap.
return RETRY;
}
long heapDumpDurationMs = NANOSECONDS.toMillis(System.nanoTime() - startDumpHeap);
HeapDump heapDump = heapDumpBuilder.heapDumpFile(heapDumpFile).referenceKey(reference.key)
.referenceName(reference.name)
.watchDurationMs(watchDurationMs)
.gcDurationMs(gcDurationMs)
.heapDumpDurationMs(heapDumpDurationMs)
.build();
//将hprof进行分析出泄漏的点并通过ui通知用户
heapdumpListener.analyze(heapDump);
}
return DONE;
}
参考
https://allenwu.itscoder.com/leakcanary-source
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