这个跟message有什么关系？looper实例都还没有，哪里来的Message?

   @Override

    public void run() {

        mTid = Process.myTid();

        Looper.prepare();

        synchronized (this) {

            mLooper = Looper.myLooper();

            notifyAll();

        }

        Process.setThreadPriority(mPriority);

        onLooperPrepared();

        Looper.loop();

        mTid = -1;

    }

    /**

     * This method returns the Looper associated with this thread. If this thread not been started

     * or for any reason is 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) {

                try {

                    wait();

                } catch (InterruptedException e) {

                }

            }

        }

        return mLooper;

    }

如果在getLooper()并且run()还没有运行起来，这个时候wait()了，阻塞了，然后这个线程还怎么去返过来执行run()。我问的是这个

messagequeue为空的时候才会阻塞，不为空的时候是不会阻塞的。