LeakCanary的原理，你知道么？
LeakCanary 是由 Square 开源的针对 Android 和 Java 的内存泄漏检测工具。
使用
LeakCanary 的集成过程很简单，首先在 build.gradle 文件中添加依赖：
dependencies {
debugImplementation 'com.squareup.leakcanary:leakcanary-android:1.5.4'
releaseImplementation 'com.squareup.leakcanary:leakcanary-android-no-op:1.5.4'
}
debug 和 release 版本中使用的是不同的库。LeakCanary 运行时会经常执行 GC 操作，在 release 版本中会影响效率。android-no-op 版本中基本没有逻辑实现，用于 release 版本。
然后实现自己的 Application 类：
public class ExampleApplication extends Application {
@Override public void onCreate() {
super.onCreate();
if (LeakCanary.isInAnalyzerProcess(this)) {
// This process is dedicated to LeakCanary for heap analysis.
// You should not init your app in this process.
return;
}
LeakCanary.install(this);
// Normal app init code...
}
}
这样就集成完成了。当 LeakCanary 检测到内存泄露时，会自动弹出 Notification 通知开发者发生内存泄漏的 Activity 和引用链，以便进行修复。
源码分析
从入口函数 LeakCanary.install(this) 开始分析：
LeakCanary.install
LeakCanary.java
/**
* Creates a {@link RefWatcher} that works out of the box, and starts watching activity
* references (on ICS+).
*/
public static RefWatcher install(Application application) {
return refWatcher(application).listenerServiceClass(DisplayLeakService.class)
.excludedRefs(AndroidExcludedRefs.createAppDefaults().build())
.buildAndInstall();
}
LeakCanary.refWatcherLeakCanary.java
/** Builder to create a customized {@link RefWatcher} with appropriate Android defaults. */
public static AndroidRefWatcherBuilder refWatcher(Context context) {
return new AndroidRefWatcherBuilder(context);
}
refWatcher() 方法新建了一个 AndroidRefWatcherBuilder 对象，该对象继承于 RefWatcherBuilder 类，配置了一些默认参数，利用建造者构建一个 RefWatcher 对象。
AndroidRefWatcherBuilder.listenerServiceClassAndroidRefWatcherBuilder.java
public AndroidRefWatcherBuilder listenerServiceClass(
Class<? extends AbstractAnalysisResultService> listenerServiceClass) {
return heapDumpListener(new ServiceHeapDumpListener(context, listenerServiceClass));
}
RefWatcherBuilder.java
/** @see HeapDump.Listener */
public final T heapDumpListener(HeapDump.Listener heapDumpListener) {
this.heapDumpListener = heapDumpListener;
return self();
}
DisplayLeakService.java
/**
* Logs leak analysis results, and then shows a notification which will start {@link
* DisplayLeakActivity}.
*
* You can extend this class and override {@link #afterDefaultHandling(HeapDump, AnalysisResult,
* String)} to add custom behavior, e.g. uploading the heap dump.
*/
public class DisplayLeakService extends AbstractAnalysisResultService {}
listenerServiceClass() 方法绑定了一个后台服务 DisplayLeakService，这个服务主要用来分析内存泄漏结果并发送通知。你可以继承并重写这个类来进行一些自定义操作，比如上传分析结果等。
RefWatcherBuilder.excludedRefsRefWatcherBuilder.java
public final T excludedRefs(ExcludedRefs excludedRefs) {
this.excludedRefs = excludedRefs;
return self();
}
AndroidExcludedRefs.java
/**
* This returns the references in the leak path that can be ignored for app developers. This
* doesn't mean there is no memory leak, to the contrary. However, some leaks are caused by bugs
* in AOSP or manufacturer forks of AOSP. In such cases, there is very little we can do as app
* developers except by resorting to serious hacks, so we remove the noise caused by those leaks.
*/
public static ExcludedRefs.Builder createAppDefaults() {
return createBuilder(EnumSet.allOf(AndroidExcludedRefs.class));
}
public static ExcludedRefs.Builder createBuilder(EnumSet<AndroidExcludedRefs> refs) {
ExcludedRefs.Builder excluded = ExcludedRefs.builder();
for (AndroidExcludedRefs ref : refs) {
if (ref.applies) {
ref.add(excluded);
((ExcludedRefs.BuilderWithParams) excluded).named(ref.name());
}
}
return excluded;
}
excludedRefs() 方法定义了一些对于开发者可以忽略的路径，意思就是即使这里发生了内存泄漏，LeakCanary 也不会弹出通知。这大多是系统 Bug 导致的，无需用户进行处理。
AndroidRefWatcherBuilder.buildAndInstall
最后调用 buildAndInstall() 方法构建 RefWatcher 实例并开始监听 Activity 的引用：
AndroidRefWatcherBuilder.java
/**
* Creates a {@link RefWatcher} instance and starts watching activity references (on ICS+).
*/
public RefWatcher buildAndInstall() {
RefWatcher refWatcher = build();
if (refWatcher != DISABLED) {
LeakCanary.enableDisplayLeakActivity(context);
ActivityRefWatcher.install((Application) context, refWatcher);
}
return refWatcher;
}
看一下主要的 build() 和 install() 方法：
RefWatcherBuilder.build
RefWatcherBuilder.java
/** Creates a {@link RefWatcher}. */
public final RefWatcher build() {
if (isDisabled()) {
return RefWatcher.DISABLED;
}
ExcludedRefs excludedRefs = this.excludedRefs;
if (excludedRefs == null) {
excludedRefs = defaultExcludedRefs();
}
HeapDump.Listener heapDumpListener = this.heapDumpListener;
if (heapDumpListener == null) {
heapDumpListener = defaultHeapDumpListener();
}
DebuggerControl debuggerControl = this.debuggerControl;
if (debuggerControl == null) {
debuggerControl = defaultDebuggerControl();
}
HeapDumper heapDumper = this.heapDumper;
if (heapDumper == null) {
heapDumper = defaultHeapDumper();
}
WatchExecutor watchExecutor = this.watchExecutor;
if (watchExecutor == null) {
watchExecutor = defaultWatchExecutor();
}
GcTrigger gcTrigger = this.gcTrigger;
if (gcTrigger == null) {
gcTrigger = defaultGcTrigger();
}
return new RefWatcher(watchExecutor, debuggerControl, gcTrigger, heapDumper, heapDumpListener,
excludedRefs);
}
build() 方法利用建造者模式构建 RefWatcher 实例，看一下其中的主要参数：
watchExecutor: 线程控制器，在onDestroy()之后并且主线程空闲时执行内存泄漏检测debuggerControl: 判断是否处于调试模式，调试模式中不会进行内存泄漏检测gcTrigger: 用于GC，watchExecutor首次检测到可能的内存泄漏，会主动进行GC，GC之后会再检测一次，仍然泄漏的判定为内存泄漏，进行后续操作heapDumper:dump内存泄漏处的heap信息，写入hprof文件heapDumpListener: 解析完hprof文件并通知DisplayLeakService弹出提醒excludedRefs: 排除可以忽略的泄漏路径
接下来就是最核心的 install() 方法，这里就开始观察 Activity 的引用了。在这之前还执行了一步操作，LeakCanary.enableDisplayLeakActivity(context); ：
public static void enableDisplayLeakActivity(Context context) {
setEnabled(context, DisplayLeakActivity.class, true);
}
最后执行到 LeakCanaryInternals#setEnabledBlocking ：
public static void setEnabledBlocking(Context appContext, Class<?> componentClass,
boolean enabled) {
ComponentName component = new ComponentName(appContext, componentClass);
PackageManager packageManager = appContext.getPackageManager();
int newState = enabled ? COMPONENT_ENABLED_STATE_ENABLED : COMPONENT_ENABLED_STATE_DISABLED;
// Blocks on IPC.
packageManager.setComponentEnabledSetting(component, newState, DONT_KILL_APP);
}
这里启用了 DisplayLeakActivity 并且显示应用图标。注意，这是指的不是你自己的应用图标，是一个单独的 LeakCanary 的应用，用于展示内存泄露历史的，入口函数是 DisplayLeakActivity，在 AndroidManifest.xml 中可以看到默认情况下 android:enabled="false" :
<activity
android:theme="@style/leak_canary_LeakCanary.Base"
android:name=".internal.DisplayLeakActivity"
android:process=":leakcanary"
android:enabled="false"
android:label="@string/leak_canary_display_activity_label"
android:icon="@mipmap/leak_canary_icon"
android:taskAffinity="com.squareup.leakcanary.${applicationId}"
>
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>
</activity>
ActivityRefWatcher.install
ActivityRefWatcher.java
public static void install(Application application, RefWatcher refWatcher) {
new ActivityRefWatcher(application, refWatcher).watchActivities();
}
public void watchActivities() {
// Make sure you don't get installed twice.
stopWatchingActivities();
application.registerActivityLifecycleCallbacks(lifecycleCallbacks);
}
watchActivities() 方法中先解绑生命周期回调注册 lifecycleCallbacks，再重新绑定，避免重复绑定。lifecycleCallbacks 监听了 Activity 的各个生命周期，在 onDestroy() 中开始检测当前 Activity 的引用。
private final Application.ActivityLifecycleCallbacks lifecycleCallbacks =
new Application.ActivityLifecycleCallbacks() {
@Override public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
}
@Override public void onActivityStarted(Activity activity) {
}
@Override public void onActivityResumed(Activity activity) {
}
@Override public void onActivityPaused(Activity activity) {
}
@Override public void onActivityStopped(Activity activity) {
}
@Override public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
}
@Override public void onActivityDestroyed(Activity activity) {
ActivityRefWatcher.this.onActivityDestroyed(activity);
}
};
void onActivityDestroyed(Activity activity) {
refWatcher.watch(activity);
}
下面着重分析 RefWatcher 是如何检测 Activity 的。
RefWatcher.watch
调用 RefWatcher#watch 检测 Activity。RefWatcher.java
/**
* Identical to {@link #watch(Object, String)} with an empty string reference name.
*
* @see #watch(Object, String)
*/
public void watch(Object watchedReference) {
watch(watchedReference, "");
}
/**
* Watches the provided references and checks if it can be GCed. This method is non blocking,
* the check is done on the {@link WatchExecutor} this {@link RefWatcher} has been constructed
* with.
*
* @param referenceName An logical identifier for the watched object.
*/
public void watch(Object watchedReference, String referenceName) {
if (this == DISABLED) {
return;
}
checkNotNull(watchedReference, "watchedReference");
checkNotNull(referenceName, "referenceName");
final long watchStartNanoTime = System.nanoTime();
String key = UUID.randomUUID().toString();
retainedKeys.add(key);
final KeyedWeakReference reference =
new KeyedWeakReference(watchedReference, key, referenceName, queue);
ensureGoneAsync(watchStartNanoTime, reference);
}
watch() 方法的参数是 Object ，LeakCanary 并不仅仅是针对 Android 的，它可以检测任何对象的内存泄漏，原理都是一致的。
这里出现了几个新面孔，先来了解一下各自是什么：
retainedKeys: 一个Set<String>集合，每个检测的对象都对应着一个唯一的key，存储在retainedKeys中KeyedWeakReference: 自定义的弱引用，持有检测对象和对用的key值
final class KeyedWeakReference extends WeakReference<Object> {
public final String key;
public final String name;
KeyedWeakReference(Object referent, String key, String name,
ReferenceQueue<Object> referenceQueue) {
super(checkNotNull(referent, "referent"), checkNotNull(referenceQueue, "referenceQueue"));
this.key = checkNotNull(key, "key");
this.name = checkNotNull(name, "name");
}
}
queue:ReferenceQueue对象，和KeyedWeakReference配合使用
这里有个小知识点，弱引用和引用队列 ReferenceQueue 联合使用时，如果弱引用持有的对象被垃圾回收，Java 虚拟机就会把这个弱引用加入到与之关联的引用队列中。即 KeyedWeakReference 持有的 Activity 对象如果被垃圾回收，该对象就会加入到引用队列 queue 中。
接着看看具体的内存泄漏判断过程：
RefWatcher.ensureGoneAsync
private void ensureGoneAsync(final long watchStartNanoTime, final KeyedWeakReference reference) {
watchExecutor.execute(new Retryable() {
@Override public Retryable.Result run() {
return ensureGone(reference, watchStartNanoTime);
}
});
}
通过 watchExecutor 执行检测操作，这里的 watchExecutor 是 AndroidWatchExecutor 对象。
@Override protected WatchExecutor defaultWatchExecutor() {
return new AndroidWatchExecutor(DEFAULT_WATCH_DELAY_MILLIS);
}
DEFAULT_WATCH_DELAY_MILLIS 为 5 s。
public AndroidWatchExecutor(long initialDelayMillis) {
mainHandler = new Handler(Looper.getMainLooper());
HandlerThread handlerThread = new HandlerThread(LEAK_CANARY_THREAD_NAME);
handlerThread.start();
backgroundHandler = new Handler(handlerThread.getLooper());
this.initialDelayMillis = initialDelayMillis;
maxBackoffFactor = Long.MAX_VALUE / initialDelayMillis;
}
看看其中用到的几个对象：
mainHandler: 主线程消息队列handlerThread: 后台线程，HandlerThread对象，线程名为LeakCanary-Heap-DumpbackgroundHandler: 上面的后台线程的消息队列initialDelayMillis: 5 s，即之前的DEFAULT_WATCH_DELAY_MILLIS
@Override public void execute(Retryable retryable) {
if (Looper.getMainLooper().getThread() == Thread.currentThread()) {
waitForIdle(retryable, 0);
} else {
postWaitForIdle(retryable, 0);
}
}
void postWaitForIdle(final Retryable retryable, final int failedAttempts) {
mainHandler.post(new Runnable() {
@Override public void run() {
waitForIdle(retryable, failedAttempts);
}
});
}
void waitForIdle(final Retryable retryable, final int failedAttempts) {
// This needs to be called from the main thread.
Looper.myQueue().addIdleHandler(new MessageQueue.IdleHandler() {
@Override public boolean queueIdle() {
postToBackgroundWithDelay(retryable, failedAttempts);
return false;
}
});
}
在具体的 execute() 过程中，不管是 waitForIdle 还是 postWaitForIdle，最终还是要切换到主线程中执行。要注意的是，这里的 IdleHandler 到底是什么时候去执行？
我们都知道 Handler 是循环处理 MessageQueue 中的消息的，当消息队列中没有更多消息需要处理的时候，且声明了 IdleHandler 接口，这是就会去处理这里的操作。即指定一些操作，当线程空闲的时候来处理。当主线程空闲时，就会通知后台线程延时 5 秒执行内存泄漏检测工作。
void postToBackgroundWithDelay(final Retryable retryable, final int failedAttempts) {
long exponentialBackoffFactor = (long) Math.min(Math.pow(2, failedAttempts), maxBackoffFactor);
long delayMillis = initialDelayMillis * exponentialBackoffFactor;
backgroundHandler.postDelayed(new Runnable() {
@Override public void run() {
Retryable.Result result = retryable.run();
if (result == RETRY) {
postWaitForIdle(retryable, failedAttempts + 1);
}
}
}, delayMillis);
}
下面是真正的检测过程，AndroidWatchExecutor 在执行时调用 ensureGone() 方法：
RefWatcher.ensureGone
Retryable.Result ensureGone(final KeyedWeakReference reference, final long watchStartNanoTime) {
long gcStartNanoTime = System.nanoTime();
long watchDurationMs = NANOSECONDS.toMillis(gcStartNanoTime - watchStartNanoTime);
removeWeaklyReachableReferences();
if (debuggerControl.isDebuggerAttached()) {
// The debugger can create false leaks.
return RETRY;
}
if (gone(reference)) {
return DONE;
}
gcTrigger.runGc();
removeWeaklyReachableReferences();
if (!gone(reference)) {
long startDumpHeap = System.nanoTime();
long gcDurationMs = NANOSECONDS.toMillis(startDumpHeap - gcStartNanoTime);
File heapDumpFile = heapDumper.dumpHeap();
if (heapDumpFile == RETRY_LATER) {
// Could not dump the heap.
return RETRY;
}
long heapDumpDurationMs = NANOSECONDS.toMillis(System.nanoTime() - startDumpHeap);
heapdumpListener.analyze(
new HeapDump(heapDumpFile, reference.key, reference.name, excludedRefs, watchDurationMs,
gcDurationMs, heapDumpDurationMs));
}
return DONE;
}
再重复一次几个变量的含义，retainedKeys 是一个 Set集合，存储检测对象对应的唯一 key 值，queue是一个引用队列，存储被垃圾回收的对象。
主要过程有一下几步：
RefWatcher.emoveWeaklyReachableReferences()
private void removeWeaklyReachableReferences() {
// 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.
KeyedWeakReference ref;
while ((ref = (KeyedWeakReference) queue.poll()) != null) {
retainedKeys.remove(ref.key);
}
}
遍历引用队列 queue，判断队列中是否存在当前 Activity 的弱引用，存在则删除 retainedKeys 中对应的引用的 key值。
RefWatcher.gone()
private boolean gone(KeyedWeakReference reference) {
return !retainedKeys.contains(reference.key);
}
判断 retainedKeys 中是否包含当前 Activity 引用的 key 值。
如果不包含，说明上一步操作中 retainedKeys 移除了该引用的 key 值，也就说上一步操作之前引用队列 queue 中包含该引用，GC 处理了该引用，未发生内存泄漏，返回 DONE，不再往下执行。
如果包含，并不会立即判定发生内存泄漏，可能存在某个对象已经不可达，但是尚未进入引用队列 queue。这时会主动执行一次 GC 操作之后再次进行判断。
gcTrigger.runGc()
/**
* Called when a watched reference is expected to be weakly reachable, but hasn't been enqueued
* in the reference queue yet. This gives the application a hook to run the GC before the {@link
* RefWatcher} checks the reference queue again, to avoid taking a heap dump if possible.
*/
public interface GcTrigger {
GcTrigger DEFAULT = new GcTrigger() {
@Override public void runGc() {
// Code taken from AOSP FinalizationTest:
// https://android.googlesource.com/platform/libcore/+/master/support/src/test/java/libcore/
// java/lang/ref/FinalizationTester.java
// System.gc() does not garbage collect every time. Runtime.gc() is
// more likely to perfom a gc.
Runtime.getRuntime().gc();
enqueueReferences();
System.runFinalization();
}
private void enqueueReferences() {
// Hack. We don't have a programmatic way to wait for the reference queue daemon to move
// references to the appropriate queues.
try {
Thread.sleep(100);
} catch (InterruptedException e) {
throw new AssertionError();
}
}
};
void runGc();
}
注意这里调用 GC 的写法，并不是使用 System.gc。System.gc 仅仅只是通知系统在合适的时间进行一次垃圾回收操作，实际上并不能保证一定执行。
主动进行 GC 之后会再次进行判定，过程同上。首先调用 removeWeaklyReachableReferences() 清除 retainedKeys 中弱引用的 key 值，再判断是否移除。如果仍然没有移除，判定为内存泄漏。
内存泄露结果处理
AndroidHeapDumper.dumpHeap
判定内存泄漏之后，调用 heapDumper.dumpHeap() 进行处理：
AndroidHeapDumper.java
@SuppressWarnings("ReferenceEquality") // Explicitly checking for named null.
@Override public File dumpHeap() {
File heapDumpFile = leakDirectoryProvider.newHeapDumpFile();
if (heapDumpFile == RETRY_LATER) {
return RETRY_LATER;
}
FutureResult<Toast> waitingForToast = new FutureResult<>();
showToast(waitingForToast);
if (!waitingForToast.wait(5, SECONDS)) {
CanaryLog.d("Did not dump heap, too much time waiting for Toast.");
return RETRY_LATER;
}
Toast toast = waitingForToast.get();
try {
Debug.dumpHprofData(heapDumpFile.getAbsolutePath());
cancelToast(toast);
return heapDumpFile;
} catch (Exception e) {
CanaryLog.d(e, "Could not dump heap");
// Abort heap dump
return RETRY_LATER;
}
}
leakDirectoryProvider.newHeapDumpFile() 新建了 hprof 文件，然后调用 Debug.dumpHprofData() 方法 dump 当前堆内存并写入刚才创建的文件。
回到 RefWatcher.ensureGone() 方法中，生成 heapDumpFile 文件之后，通过 heapdumpListener 分析。
ServiceHeapDumpListener.analyze
heapdumpListener.analyze(
new HeapDump(heapDumpFile, reference.key, reference.name, excludedRefs, watchDurationMs,
gcDurationMs, heapDumpDurationMs));
这里的 heapdumpListener 是 ServiceHeapDumpListener 对象，接着进入 ServiceHeapDumpListener.runAnalysis() 方法。
@Override public void analyze(HeapDump heapDump) {
checkNotNull(heapDump, "heapDump");
HeapAnalyzerService.runAnalysis(context, heapDump, listenerServiceClass);
}
这里的 listenerServiceClass 指的是 DisplayLeakService.class，文章开头提到的 AndroidRefWatcherBuilder 中进行了配置。
@Override protected HeapDump.Listener defaultHeapDumpListener() {
return new ServiceHeapDumpListener(context, DisplayLeakService.class);
}
HeapAnalyzerService.runAnalysisHeapAnalyzerService.runAnalysis() 方法中启动了它自己，传递了两个参数，DisplayLeakService 类名和要分析的 heapDump。启动自己后，在 onHandleIntent 中进行处理。
/**
* This service runs in a separate process to avoid slowing down the app process or making it run
* out of memory.
*/
public final class HeapAnalyzerService extends IntentService {
private static final String LISTENER_CLASS_EXTRA = "listener_class_extra";
private static final String HEAPDUMP_EXTRA = "heapdump_extra";
public static void runAnalysis(Context context, HeapDump heapDump,
Class<? extends AbstractAnalysisResultService> listenerServiceClass) {
Intent intent = new Intent(context, HeapAnalyzerService.class);
intent.putExtra(LISTENER_CLASS_EXTRA, listenerServiceClass.getName());
intent.putExtra(HEAPDUMP_EXTRA, heapDump);
context.startService(intent);
}
public HeapAnalyzerService() {
super(HeapAnalyzerService.class.getSimpleName());
}
@Override protected void onHandleIntent(Intent intent) {
if (intent == null) {
CanaryLog.d("HeapAnalyzerService received a null intent, ignoring.");
return;
}
String listenerClassName = intent.getStringExtra(LISTENER_CLASS_EXTRA);
HeapDump heapDump = (HeapDump) intent.getSerializableExtra(HEAPDUMP_EXTRA);
HeapAnalyzer heapAnalyzer = new HeapAnalyzer(heapDump.excludedRefs);
AnalysisResult result = heapAnalyzer.checkForLeak(heapDump.heapDumpFile, heapDump.referenceKey);
AbstractAnalysisResultService.sendResultToListener(this, listenerClassName, heapDump, result);
}
}
heapAnalyzer.checkForLeak
checkForLeak 方法中主要使用了 Square 公司的另一个库 haha 来分析 Android heap dump，得到结果后回调给 DisplayLeakService。
AbstractAnalysisResultService.sendResultToListener
public static void sendResultToListener(Context context, String listenerServiceClassName,
HeapDump heapDump, AnalysisResult result) {
Class<?> listenerServiceClass;
try {
listenerServiceClass = Class.forName(listenerServiceClassName);
} catch (ClassNotFoundException e) {
throw new RuntimeException(e);
}
Intent intent = new Intent(context, listenerServiceClass);
intent.putExtra(HEAP_DUMP_EXTRA, heapDump);
intent.putExtra(RESULT_EXTRA, result);
context.startService(intent);
}
同样在 onHandleIntent 中进行处理。
DisplayLeakService.onHandleIntent
@Override protected final void onHandleIntent(Intent intent) {
HeapDump heapDump = (HeapDump) intent.getSerializableExtra(HEAP_DUMP_EXTRA);
AnalysisResult result = (AnalysisResult) intent.getSerializableExtra(RESULT_EXTRA);
try {
onHeapAnalyzed(heapDump, result);
} finally {
//noinspection ResultOfMethodCallIgnored
heapDump.heapDumpFile.delete();
}
}
DisplayLeakService.onHeapAnalyzed
调用 onHeapAnalyzed() 之后，会将 hprof 文件删除。
DisplayLeakService.java
@Override protected final void onHeapAnalyzed(HeapDump heapDump, AnalysisResult result) {
String leakInfo = leakInfo(this, heapDump, result, true);
CanaryLog.d("%s", leakInfo);
boolean resultSaved = false;
boolean shouldSaveResult = result.leakFound || result.failure != null;
if (shouldSaveResult) {
heapDump = renameHeapdump(heapDump);
resultSaved = saveResult(heapDump, result);
}
PendingIntent pendingIntent;
String contentTitle;
String contentText;
if (!shouldSaveResult) {
contentTitle = getString(R.string.leak_canary_no_leak_title);
contentText = getString(R.string.leak_canary_no_leak_text);
pendingIntent = null;
} else if (resultSaved) {
pendingIntent = DisplayLeakActivity.createPendingIntent(this, heapDump.referenceKey);
if (result.failure == null) {
String size = formatShortFileSize(this, result.retainedHeapSize);
String className = classSimpleName(result.className);
if (result.excludedLeak) {
contentTitle = getString(R.string.leak_canary_leak_excluded, className, size);
} else {
contentTitle = getString(R.string.leak_canary_class_has_leaked, className, size);
}
} else {
contentTitle = getString(R.string.leak_canary_analysis_failed);
}
contentText = getString(R.string.leak_canary_notification_message);
} else {
contentTitle = getString(R.string.leak_canary_could_not_save_title);
contentText = getString(R.string.leak_canary_could_not_save_text);
pendingIntent = null;
}
// New notification id every second.
int notificationId = (int) (SystemClock.uptimeMillis() / 1000);
showNotification(this, contentTitle, contentText, pendingIntent, notificationId);
afterDefaultHandling(heapDump, result, leakInfo);
}
根据分析结果，调用 showNotification() 方法构建了一个 Notification 向开发者通知内存泄漏。
public static void showNotification(Context context, CharSequence contentTitle,
CharSequence contentText, PendingIntent pendingIntent, int notificationId) {
NotificationManager notificationManager =
(NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
Notification notification;
Notification.Builder builder = new Notification.Builder(context) //
.setSmallIcon(R.drawable.leak_canary_notification)
.setWhen(System.currentTimeMillis())
.setContentTitle(contentTitle)
.setContentText(contentText)
.setAutoCancel(true)
.setContentIntent(pendingIntent);
if (SDK_INT >= O) {
String channelName = context.getString(R.string.leak_canary_notification_channel);
setupNotificationChannel(channelName, notificationManager, builder);
}
if (SDK_INT < JELLY_BEAN) {
notification = builder.getNotification();
} else {
notification = builder.build();
}
notificationManager.notify(notificationId, notification);
}
DisplayLeakService.afterDefaultHandling
最后还会执行一个空实现的方法 afterDefaultHandling：
/**
* You can override this method and do a blocking call to a server to upload the leak trace and
* the heap dump. Don't forget to check {@link AnalysisResult#leakFound} and {@link
* AnalysisResult#excludedLeak} first.
*/
protected void afterDefaultHandling(HeapDump heapDump, AnalysisResult result, String leakInfo) {
}
你可以重写这个方法进行一些自定义的操作，比如向服务器上传泄漏的堆栈信息等。
这样，LeakCanary 就完成了整个内存泄漏检测的过程。可以看到，LeakCanary 的设计思路十分巧妙，同时也很清晰，有很多有意思的知识点，像对于弱引用和 ReferenceQueue 的使用， IdleHandler 的使用，四大组件的开启和关闭等等，都很值的大家去深究。
原创投稿：孙路遥
原文链接：https://www.jianshu.com/p/751f99918711