HandlerThread使用及原理

首先看一下继承接口

从上面截图中可以看到他是个线程类,既然是线程类那么先看到run方法

    @Override
    public void run() {
        mTid = Process.myTid();
        //创建当前线程的Looper对象
        Looper.prepare();
        synchronized (this) {
            mLooper = Looper.myLooper();
            notifyAll();
        }
        Process.setThreadPriority(mPriority);
        onLooperPrepared();
        //启动轮询
        Looper.loop();
        mTid = -1;
    }

在run方法中主要就是创建Looper和启动looper的消息分发,看到了Looper那自然避不开Handler

 

    /**
     * @return a shared {@link Handler} associated with this thread
     * @hide
     */
    @NonNull
    public Handler getThreadHandler() {
        if (mHandler == null) {
            mHandler = new Handler(getLooper());
        }
        return mHandler;
    }

在HandlerThread中就有一个获取当前Handler的方法,这个方法被带上的hide注解我们在开发中无法自己调用需要新建handler传入Looper如下代码

        val handlerThread = HandlerThread("handleThread")
        handlerThread.start()
        val looper = handlerThread.looper
        Handler(looper).post {
            Log.e(tag, "onCreate: ${Thread.currentThread().name}")
        }

用这个Handler发送的消息就会在这个新建的线程中执行,这里有个则是通过HandlerThread#getLooper之前需要先调用线程的Thread#start让其先执行run方法不然会阻塞进入wait状态

    public Looper getLooper() {
        if (!isAlive()) {
            return null;
        }

        boolean wasInterrupted = false;

        // If the thread has been started, wait until the looper has been created.
        synchronized (this) {
            //mLooper会在run方法中被创建
            while (isAlive() && mLooper == null) {
                try {
                    wait();
                } catch (InterruptedException e) {
                    wasInterrupted = true;
                }
            }
        }

        /*
         * We may need to restore the thread's interrupted flag, because it may
         * have been cleared above since we eat InterruptedExceptions
         */
        if (wasInterrupted) {
            Thread.currentThread().interrupt();
        }

        return mLooper;
    }

 结合上面看到的源码总结出HandlerThread就是Thread+Handler是个适合执行耗时任务的Handler