CyclicBarrier

基本介绍

循环栅栏，用来进行线程协作，等待线程满足某个计数。构造时设置『计数个数』，每个线程执行到某个需要“同步”的时刻调用 await() 方法进行等待，当等待的线程数满足『计数个数』时，继续执行

功能和 countdownlatch 一样, 但是 CyclicBarrier 可以循环使用

基本使用

CountdownLatch实现

private static void test01() {
        ExecutorService service = Executors.newFixedThreadPool(3);

        for (int i = 0; i < 5; i++) {
            CountDownLatch latch = new CountDownLatch(2);
            service.submit(() -> {
                log.debug("start ... ");
                latch.countDown();
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
                log.debug("end ... ");
            });
            service.submit(() -> {
                log.debug("start ... ");
                latch.countDown();
                try {
                    TimeUnit.SECONDS.sleep(2);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
                log.debug("end ... ");
            });
            service.submit(() -> {
                log.debug("sum start ... ");
                try {
                    latch.await();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
                log.debug("sum end ... ");
            });
        }

        service.shutdown();
    }

可以看到上面的代码我们在每次循环的时候 , 都需要创建 CountDownLatch latch = new CountDownLatch(2);

CyclicBarrier实现

public static void main(String[] args) {

        // test01();
        ExecutorService service = Executors.newFixedThreadPool(2);
        CyclicBarrier barrier = new CyclicBarrier(2, () -> {
            log.debug("task1 , task2 finish ... ");
        });

        for (int i = 0; i < 5; i++) {
            service.submit(() -> {
                log.debug("task1 start ... ");
                try {
                    TimeUnit.SECONDS.sleep(1);

                    barrier.await(); // 2 - 1

                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                } catch (BrokenBarrierException e) {
                    throw new RuntimeException(e);
                }
                log.debug("end ... ");
            });
            service.submit(() -> {
                log.debug("task2 start ... ");
                try {
                    TimeUnit.SECONDS.sleep(2);
                    barrier.await(); // 1 - 1
                } catch (InterruptedException | BrokenBarrierException e) {
                    throw new RuntimeException(e);
                }
                log.debug("end ... ");
            });
        }

        service.shutdown();
    }

CyclicBarrier 相当于是人满发车, 比如 设置的大小是 2的时候, 只有执行 barrier.await() 的是2的时候, 线程才会向下执行,

14:18:57.402 [pool-1-thread-2] DEBUG c.CyclicBarrierTest - task2 start ... 
14:18:57.402 [pool-1-thread-1] DEBUG c.CyclicBarrierTest - task1 start ... 
14:18:59.417 [pool-1-thread-2] DEBUG c.CyclicBarrierTest - task1 , task2 finish ... 
14:18:59.417 [pool-1-thread-2] DEBUG c.CyclicBarrierTest - end ... 
14:18:59.417 [pool-1-thread-1] DEBUG c.CyclicBarrierTest - end ... 

可以看到执行结果, task1 和 task2 等待的时间不同, 一个是1s, 一个是2s, 但是他们都是同时结束的