public HandlerThread(String name) {
    super(name);
    mPriority = Process.THREAD_PRIORITY_DEFAULT;
}

/**
 * Constructs a HandlerThread.
 * @param name
 * @param priority The priority to run the thread at. The value supplied must be from 
 * {@link android.os.Process} and not from java.lang.Thread.
 */
public HandlerThread(String name, int priority) {
    super(name);
    mPriority = priority;//设置优先级
}

/**
    * Call back method that can be explicitly overridden if needed to execute some
    * setup before Looper loops.
    */
   protected void onLooperPrepared() {
   }

@Override
    public void run() {
        mTid = Process.myTid();
        Looper.prepare();//  初始化looper
        synchronized (this) {// 保证线程间数据安全
            mLooper = Looper.myLooper();
            notifyAll();// 通知当前等待的线程
        }
        Process.setThreadPriority(mPriority);// 给线程设定优先级(可以解决内存泄露*1)
        onLooperPrepared();
        Looper.loop();// 开启循环
        mTid = -1;
    }

/**
     * This method returns the Looper associated with this thread. If this thread not been started
     * or for any reason isAlive() returns false, this method will return null. If this thread
     * has been started, this method will block until the looper has been initialized.  
     * @return The looper.
     */
    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) { // 如果looper没创建成功则一直阻塞
                try {
                    wait();// 被run()方法中的notifyAll()通知
                } catch (InterruptedException e) {
                }
            }
        }
        return mLooper;
    }

/**
    * Quits the handler thread's looper.
    * <p>
    * Causes the handler thread's looper to terminate without processing any
    * more messages in the message queue.
    * </p><p>
    * Any attempt to post messages to the queue after the looper is asked to quit will fail.
    * For example, the {@link Handler#sendMessage(Message)} method will return false.
    * </p><p class="note">
    * Using this method may be unsafe because some messages may not be delivered
    * before the looper terminates.  Consider using {@link #quitSafely} instead to ensure
    * that all pending work is completed in an orderly manner.
    * </p>
    *
    * @return True if the looper looper has been asked to quit or false if the
    * thread had not yet started running.
    *
    * @see #quitSafely
    */
   public boolean quit() {
       Looper looper = getLooper();
       if (looper != null) {
           looper.quit();
           return true;
       }
       return false;
   }

/**
    * Quits the handler thread's looper safely.
    * <p>
    * Causes the handler thread's looper to terminate as soon as all remaining messages
    * in the message queue that are already due to be delivered have been handled.
    * Pending delayed messages with due times in the future will not be delivered.
    * </p><p>
    * Any attempt to post messages to the queue after the looper is asked to quit will fail.
    * For example, the {@link Handler#sendMessage(Message)} method will return false.
    * </p><p>
    * If the thread has not been started or has finished (that is if
    * {@link #getLooper} returns null), then false is returned.
    * Otherwise the looper is asked to quit and true is returned.
    * </p>
    *
    * @return True if the looper looper has been asked to quit or false if the
    * thread had not yet started running.
    */
   public boolean quitSafely() {
       Looper looper = getLooper();
       if (looper != null) {
           looper.quitSafely();
           return true;
       }
       return false;
   }