IdleHandler的使用及原理（idle是干什么用的）

        Looper.myQueue().addIdleHandler(object: MessageQueue.IdleHandler {
            override fun queueIdle(): Boolean {
                //执行任务
                return false;
            }
        })

public final class MessageQueue {

    private final ArrayList<IdleHandler> mIdleHandlers = new ArrayList<IdleHandler>();
  
 
     /**
     * Add a new {@link IdleHandler} to this message queue.  This may be
     * removed automatically for you by returning false from
     * {@link IdleHandler#queueIdle IdleHandler.queueIdle()} when it is
     * invoked, or explicitly removing it with {@link #removeIdleHandler}.
     *
     * <p>This method is safe to call from any thread.
     *
     * @param handler The IdleHandler to be added.
     */
    public void addIdleHandler(@NonNull IdleHandler handler) {
        if (handler == null) {
            throw new NullPointerException("Can't add a null IdleHandler");
        }
        synchronized (this) {
            mIdleHandlers.add(handler);
        }
    }
 
 
    /**
     * Callback interface for discovering when a thread is going to block
     * waiting for more messages.
     */
    public static interface IdleHandler {
        boolean queueIdle();
    }
}

    @UnsupportedAppUsage
    Message next() {
        ...
        int pendingIdleHandlerCount = -1; // -1 only during first iteration
        int nextPollTimeoutMillis = 0;
        for (;;) {
            if (nextPollTimeoutMillis != 0) {
                Binder.flushPendingCommands();
            }

            nativePollOnce(ptr, nextPollTimeoutMillis);

            synchronized (this) {
                ...
                if (msg != null) {
                 ...

                // If first time idle, then get the number of idlers to run.
                // Idle handles only run if the queue is empty or if the first message
                // in the queue (possibly a barrier) is due to be handled in the future.
                if (pendingIdleHandlerCount < 0
                        && (mMessages == null || now < mMessages.when)) {
                   //如果消息队列为空或者消息执行时间还未到，则获取IdleHandler队列的大小，下面需要用到
                    pendingIdleHandlerCount = mIdleHandlers.size();
                }
                if (pendingIdleHandlerCount <= 0) {
                    // No idle handlers to run.  Loop and wait some more.
                   //无需要执行的  idle handler，则继续阻塞
                    mBlocked = true;
                    continue;
                }

                if (mPendingIdleHandlers == null) {
                    mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];
                }
                //将IdleHandler列表转为数组
                mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
            }

            // Run the idle handlers.
            // We only ever reach this code block during the first iteration.
            for (int i = 0; i < pendingIdleHandlerCount; i++) {
                final IdleHandler idler = mPendingIdleHandlers[i];
                mPendingIdleHandlers[i] = null; // release the reference to the handler

                boolean keep = false;
                try {
                    keep = idler.queueIdle();   //开始顺序执行所有IdleHandler的queueIdle方法
                } catch (Throwable t) {
                    Log.wtf(TAG, "IdleHandler threw exception", t);
                }

                if (!keep) {   //如果发现有queueIdle()方法返回false，则线程安全地删除这个idlehandler不再执行queueIdle
                    synchronized (this) {
                        mIdleHandlers.remove(idler);
                    }
                }
            }
            ...
        }
    }

public class TaskDispatcher {

    private Queue<Runnable> delayTasks = new LinkedList<>();

    private MessageQueue.IdleHandler idleHandler = () -> {
        if (delayTasks.size() > 0) {
            Runnable task = delayTasks.poll();
            if (task != null) {
                task.run();
            }
        }
        return !delayTasks.isEmpty();  //只要task任务不为空，就继续执行初始化
    };

    public TaskDispatcher addTask(Runnable task) {
        delayTasks.add(task);
        return this;
    }

    public void start() {
        Looper.myQueue().addIdleHandler(idleHandler);
    }
}

public class WebviewInitTask implements Runnable {

    @Override
    public void run() {
        Log.i("minfo", "初始化Okhttp");
    }
}

public class WebviewInitTask implements Runnable {

    @Override
    public void run() {
        Log.i("minfo", "初始化Webview");
    }
}

override fun onCreate(savedInstanceState: Bundle?) {
        setTheme(R.style.AppTheme)
        super.onCreate(savedInstanceState)
        
            TaskDispatcher()
            .addTask(ARouterInitTask())
            .addTask(WebviewInitTask())
            .start()
    }