Java - CountDownLatch与CyclicBarrier的区别

类型	定义	例子	超时例子
CountDownLatch	一个（或多个）线程等待其他线程(彼此独立)执行完成	每个人(其他线程)下班打卡（countDown）后，各回各家(彼此独立)；等人都走光后，保卫大爷（等待线程）才关门(await)	保卫大爷（等待线程）到点就关门(await)，即使还有人没下班
CyclicBarrier	多个线程互相等待，直到所有线程到达同一个同步点。并且可以重复使用（节能环保）	开会时，一般需要参会人（多个线程）都到会议室（await同步点）后，才能开会	参会人（多个线程）等待（await）一定时间后，即使有人缺席，还是要开会

CountDownLatch示例

代码

     public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        ExecutorService threadPool = Executors.newFixedThreadPool(10);
        int threadCount = 3;
        for (int i = 0; i < threadCount; i++) {
            final int threadNum = i;
            Thread.sleep(1000);
            threadPool.execute(() -> {
                try {
                    System.out.printf("开始上班::threadNum=%d time=%s %n", threadNum, getTime());
                    // 上班8毫秒（黑人问号？？？）
                    Thread.sleep(8);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.printf("打卡下班::threadNum=%d time=%s %n", threadNum, getTime());
                countDownLatch.countDown();
                System.out.printf("打卡完毕，各回各家::threadNum=%d time=%s %n", threadNum, getTime());
                System.out.println("**********\n");
            });
        }

        System.out.println("保卫大爷等待关门...");
        countDownLatch.await();
        threadPool.shutdown();
        System.out.println("保卫大爷关门回家！");
    }

    private static String getTime() {
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("HH:mm:ss S");
        return simpleDateFormat.format(new Date());
    }

结果

CyclicBarrier示例

代码

    public static void main(String[] args) throws InterruptedException {
        CyclicBarrier cyclicBarrier = new CyclicBarrier(3);
        ExecutorService threadPool = Executors.newFixedThreadPool(10);
        int threadCount = 3;
        for (int i = 0; i < threadCount; i++) {
            final int threadNum = i;
            Thread.sleep(1000);
            threadPool.execute(() -> {
                try {
                    System.out.printf("到达会议室::threadNum=%d time=%s %n", threadNum, getTime());
                    System.out.printf("已等待人数::%d 人%n", cyclicBarrier.getNumberWaiting());
                    System.out.println("**********\n");
                    cyclicBarrier.await();
                    System.out.printf("开始开会::threadNum=%d time=%s %n", threadNum, getTime());
                } catch (InterruptedException | BrokenBarrierException e) {
                    e.printStackTrace();
                }
            });
        }
        threadPool.shutdown();
    }

    private static String getTime() {
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("HH:mm:ss S");
        return simpleDateFormat.format(new Date());
    }

结果