CountDownLatch的使用示例

 

CountDownLatch基于计数器的思想,对线程的执行流程进行控制,一般用于多个任务都完成才可进行下一步的情况.

上代码:

public static void main(String[] args) {
        /**
         * 创建 CountDownLatch 并指定计数器的值为3
         */
        CountDownLatch countDownLatch = new CountDownLatch(3);
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
                3,10,10,TimeUnit.SECONDS,
                new ArrayBlockingQueue<Runnable>(1),
                new ThreadPoolExecutor.DiscardOldestPolicy());
        Runner runner = new Runner(countDownLatch);
        threadPoolExecutor.execute(runner);
        threadPoolExecutor.execute(runner);
        threadPoolExecutor.execute(runner);
        try {
            /**
             * 直到计数器的值减为0,否则一直阻塞在此处
             */
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("===The End===");
        threadPoolExecutor.shutdownNow();
    }

    static class Runner implements Runnable {

        private CountDownLatch countDownLatch;

        public Runner(CountDownLatch countDownLatch) {
            this.countDownLatch = countDownLatch;
        }

        @Override
        public void run() {
            System.out.println(Thread.currentThread().getName() + "执行");
            try {
                Thread.sleep((long) (Math.random() * 5000 + 1000));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            /**
             * 每一个线程执行一次,计数器的值减1
             */
            countDownLatch.countDown();
        }
    }