Android IntentService源码理解 及 HandlerThread构建消息循环机制分析

        // 创建HandlerThread实例
        HandlerThread handlerThread = new HandlerThread("handlerThread");
        // 启动HandlerThread线程
        handlerThread.start();
        // 构建消息循环处理机制
        Handler handler = new Handler(handlerThread.getLooper(), new Handler.Callback() {
            
            @Override
            public boolean handleMessage(Message msg) {
                return false;
            }
        });

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

    public HandlerThread(String name, int priority) {
        super(name);
        mPriority = priority;
    }

    @Override
    public void run() {
　　　　　// 获得当前线程的id
        mTid = Process.myTid();
　　　　　// 准备循环条件
        Looper.prepare();
　　　　　// 持有锁机制来获得当前线程的Looper对象
        synchronized (this) {
            mLooper = Looper.myLooper();
　　　　　　　// 发出通知，当前线程已经创建mLooper对象成功，这里主要是通知getLooper方法中的wait
            notifyAll();
        }
　　　　 // 设置当前线程的优先级
        Process.setThreadPriority(mPriority);
　　　　 // 该方法实现体是空的，子类可以实现该方法，作用就是在线程循环之前做一些准备工作，当然子类也可以不实现。　　
        onLooperPrepared();
　　　　 // 启动loop
        Looper.loop();
        mTid = -1;
    }

    public Looper getLooper() {
        if (!isAlive()) {
            return null;
        }
        
        // If the thread has been started, wait until the looper has been created.
        // 如果线程已启动，looper对象为空，则继续等待，前面的唤醒就可以唤醒当前的等待
        synchronized (this) {
            while (isAlive() && mLooper == null) {
                try {
                    wait();
                } catch (InterruptedException e) {
                }
            }
        }
        return mLooper;
    }

    public IntentService(String name) {
        super();
        mName = name;
    }

    @Override
    public void onCreate() {
        // TODO: It would be nice to have an option to hold a partial wakelock
        // during processing, and to have a static startService(Context, Intent)
        // method that would launch the service & hand off a wakelock.

        super.onCreate();
        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        thread.start();

        mServiceLooper = thread.getLooper();
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }

    @Override
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
        onStart(intent, startId);
        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
    }

    @Override
    public void onStart(@Nullable Intent intent, int startId) {
        Message msg = mServiceHandler.obtainMessage();
        msg.arg1 = startId;
        msg.obj = intent;
        mServiceHandler.sendMessage(msg);
    }

    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            onHandleIntent((Intent)msg.obj);
            stopSelf(msg.arg1);
        }
    }

    /**
     * This method is invoked on the worker thread with a request to process.
     * Only one Intent is processed at a time, but the processing happens on a
     * worker thread that runs independently from other application logic.
     * So, if this code takes a long time, it will hold up other requests to
     * the same IntentService, but it will not hold up anything else.
     * When all requests have been handled, the IntentService stops itself,
     * so you should not call {@link #stopSelf}.
     *
     * @param intent The value passed to {@link
     *               android.content.Context#startService(Intent)}.
     *               This may be null if the service is being restarted after
     *               its process has gone away; see
     *               {@link android.app.Service#onStartCommand}
     *               for details.
     */
    @WorkerThread
    protected abstract void onHandleIntent(@Nullable Intent intent);

    public final void stopSelf(int startId) {
        if (mActivityManager == null) {
            return;
        }
        try {
            mActivityManager.stopServiceToken(
                    new ComponentName(this, mClassName), mToken, startId);
        } catch (RemoteException ex) {
        }
    }

    @Override
    public void onDestroy() {
        mServiceLooper.quit();
    }