CountDownLatch 和 CyclicBarrier

public class CountDownLatchTest {

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(4);
        for(int i = 0;i < latch.getCount();i++){
            new Thread(new MyThread(latch),"player" + i).start();
        }
        System.out.println("等待 所所有玩家 准备好");
        latch.await();
        System.out.println("开始游戏");
    }


    private static class MyThread implements Runnable{
        private CountDownLatch latch;

        public MyThread(CountDownLatch latch){
            this.latch = latch;
        }
        @SneakyThrows
        @Override
        public void run() {

            Random rand = null;
            try {
                rand = new Random();
                int randomNum = rand.nextInt((3000 - 1000)  +1 ) + 1000;
                Thread.sleep(randomNum);
                System.out.println(Thread.currentThread().getName() + "已经准备好 " + "所使用的时间是：" + randomNum );
                latch.countDown();
            } catch (Exception e) {
                e.printStackTrace();
            }

        }
    }
}

public class CyclicBarrierTest {
    public static void main(String[] args) {
        CyclicBarrier barrier = new CyclicBarrier(3);
        for(int i = 0; i < barrier.getParties(); i++){
            new Thread(new MyRunnable(barrier), "队友"+i).start();
        }
        System.out.println("main function is finished.");
    }


    private static class MyRunnable implements Runnable{
        private CyclicBarrier barrier;

        public MyRunnable(CyclicBarrier barrier){
            this.barrier = barrier;
        }

        @Override
        public void run() {
            for(int i = 0; i < 3; i++) {
                try {
                    Random rand = new Random();
                    int randomNum = rand.nextInt((3000 - 1000) + 1) + 1000;//产生1000到3000之间的随机整数
                    Thread.sleep(randomNum);
                    System.out.println(Thread.currentThread().getName() + ", 通过了第"+i+"个障碍物, 使用了 "+((double)randomNum/1000)+"s");
                    this.barrier.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

总结：CountDownLatch和CyclicBarrier都有让多个线程等待同步然后再开始下一步动作的意思，但是CountDownLatch的下一步的动作实施者是主线程，具有不可重复性；而CyclicBarrier的下一步动作实施者还是“其他线程”本身，具有往复多次实施动作的特点。