HandlerThread原理分析

个人博客:

http://www.milovetingting.cn

HandlerThread是一个内部拥有Handler和Looper的特殊Thread,可以方便地在子线程中处理消息。

简单使用

HandlerThread的使用比较简单。

mHandlerThread = new HandlerThread(THREAD_NAME);
mHandlerThread.start();

首先,实例化一个HandlerThread,然后调用start()方法。在start()方法中,会调用run()方法:

@Override
public void run() {
mTid = Process.myTid();
//实例化looper对象
Looper.prepare();
synchronized (this) {
//获取looper对象
mLooper = Looper.myLooper();
//通知其它线程
notifyAll();
}
Process.setThreadPriority(mPriority);
onLooperPrepared();
//开启循环
Looper.loop();
mTid = -1;
}

然后,定义处理子线程消息的Handler:

mThreadLooper = mHandlerThread.getLooper();

mThreadHandler = new Handler(mThreadLooper, new Handler.Callback() {
@Override
public boolean handleMessage(Message msg) {
switch (msg.what) {
case MSG_THREAD_UPDATE:
//在子线程中执行耗时任务
SystemClock.sleep(3000);
mMainHandler.sendEmptyMessage(MSG_MAIN_UPDATE);
break;
default:
break;
}
return false;
}
});

在HandlerThread.getLooper()方法中:

public Looper getLooper() {
if (!isAlive()) {
return null;
} // If the thread has been started, wait until the looper has been created.
synchronized (this) {
while (isAlive() && mLooper == null) {
try {
wait();
} catch (InterruptedException e) {
}
}
}
return mLooper;
}

在getLooper()方法中,由于子线程可能还没有准备好looper,因此,会调用wait()方法等待,如果子线程looper已经准备好了,则会通过notifyAll()来唤醒。

在子线程中可以执行耗时的操作,执行完成后,可以通过在UI线程的Handler发送消息去通知UI变更。

mMainHandler.sendEmptyMessage(MSG_MAIN_UPDATE);

UI线程的Handler:

static class MainHandler extends Handler {

	//为防止内存泄漏,引入WeakReference
private WeakReference<Activity> mWeakReference; public MainHandler(Activity activity) {
mWeakReference = new WeakReference<>(activity);
} @Override
public void handleMessage(Message msg) {
MainActivity activity = (MainActivity) mWeakReference.get();
if (activity != null) {
switch (msg.what) {
case MSG_MAIN_UPDATE:
activity.updateInfo();
break;
default:
break;
}
} }
}

为防止内存泄漏,引入WeakReference。在onDestory()方法中,移除所有消息:

mMainHandler.removeCallbacksAndMessages(null);

mThreadLooper.quit();

源码地址:https://github.com/milovetingting/Samples/tree/master/HandlerThread

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