---
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);
}
```