---
怎么同步处理消息？
---

```c++
status_t Client::createSurface(const String&& name, ...){
    sp<MessageBase> msg = new MessageCreateLayer(mFlinger.get(), name, this, w, h, format, flags, handle, gbp);
    mFlinger->postMessageSync(msg);
    return static_cast<MessageCreateLayer*>(msg.get())->getResult();
}
status_t postMessageSync(const sp<MessageBase>& msg, ...){
    mEventQueue.postMessage(msg, reltime);
    msg.wait();
}
class MessageCreateLayer:public MessageBase{
    status_t getResult() const{return result;}
    virtual bool handler(){
        result = flinger->createLayer(name, client,w, h, format, ...);
        return true;
    }
}
```

```java
public final boolean runWithScissors(final Runnable r, long timeout){
	if(Looper.myLooper()==mLooper){
		r.run();
		return true;
	}
    BlockingRunnable br = new BlockingRunnable(r);
    return br.postAndWait(this, timeout);
}
private static final class BlockingRunnable implements Runnable{
    public BlockingRunnable(Runnable task){
        mTask = task;
    }
    
    @Override
    public void run(){
        mTask.run();
        mDone = true;
        notifyAll();
    }
}
public boolean postAndWait(Handler handler, ...){
    if(!handler.post(this)){
        return false;
    }
    while(!mDone){
        wait();
    }
    return true;
}
```

#### 总结

1. 同步等待消息的处理
2. Binder 调用统一切换工作线程