Create 检查线程耗时任务.md

blogs/Android/Framework/Interview/技巧心得相关/检查线程耗时任务.md

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+---
+怎么检查线程有耗时任务？
+---
+
+#### 检测机制
+
+1. WatchDog
+2. BlockCanary
+
+#### WatchDog
+
+1. 检查是否发生了死锁
+2. 检查线程是否被任务 blocked
+
+```java
+private void startOtherServices(){
+    final Watchdog watchdog = Watchdog.getInstance();
+    mActivityManagerService.systemReady(new Runnable(){
+        @Override
+        public void run(){
+            Watchdog.getInstance().start();
+        }
+    })
+}
+public class Watchdog extends Thread{...}
+
+private Watchdog(){
+    super("watchdog");
+    mMinitorChecker = new HandlerChecker(FgThread.getHandler(), ...);
+    mHandlerCheckers.add(mMinitorChecker);
+    mHandlerCheckers.add(new HandlerCheck(new Handler(Looper.getMainLooper()), ...));
+    mHandlerCheckers.add(new HandlerChecker(UiThread.getHandler(), ...));
+    mHandlerCheckers.add(new HandlerChecker(IoThread.getHandler(), ...));
+    mHandlerCheckers.add(new HandlerChecker(DisplayThread.getHandler(), ...));
+    
+    addMonitor(new BinderThreadMonitor());
+}
+```
+
+```java
+private static final class BinderThreadMonitor implements Watchdog.Monitor{
+    @Override
+    public void monitor(){
+        Binder.blockUntilThreadAvailable();
+    }
+}
+void Binder_blockUntilThreadAvailable(JNIEnv* env, jobject clazz){
+    return IPCThreadState::self()->blockUntilThreadAvailable();
+}
+void IPCThreadState::blockUntilThreadAvailable(){
+    pthread_mutex_lock(&mProcess->mThreadCountLock);
+    while(mProcess->mExecutingThreadsCount>=mProcess->mMaxThreads){
+        pthread_cond_wait(&mProcess->mThreadCountDecrement, &mProcess->mThreadCountLock);
+    }
+    pthread_mutext_unlock(&mProcess->mThreadCountLock);
+}
+status_t IPCThreadState::getAndExecuteCommand(){
+    talkWithDriver();
+    cmd = mIn.readInt32();
+    mProcess->mExecutingThreadsCount++;
+    executeCommand(cmd);
+    mProcess->mExecutingThreadsCount--;
+    mpthread_cond_broadcast(&mProcess->mThreadCountDecrement);
+}
+```
+
+```java
+// Watchdog#run
+public void run(){
+    while(true){
+        for(int i=0;i<mHandlerCheckers.size();i++){
+            HandlerChecker hc = mHandlerCheckers.get(i);
+            hc.scheduleCheckLocked();
+        }
+    }
+}
+public void scheduleCheckLocked(){
+    if(mMonitors.size()==0&&mHandler.getLooper().getQueue().isPolling()){
+        mCompleted = true;
+        return;
+    }
+    if(!mCompleted){
+        return;
+    }
+    mCompleted = false;
+    mCurrentMonitor = null;
+    mStartTime = SystemClock.uptimeMillis();
+    mHandler.postAtFromOfQueue(this);
+}
+```
+
+```java
+public ActivityManagerService(Context systemContext){
+	Watchdog.getInstance().addMonitor(this);
+    Watchdog.getInstance().addThread(mHandler);
+}
+```