CountDownLatch 介绍

类似发令枪，CountDownLatch的构造函数可以传入一个数字，代表倒计时多少个数。

主要方法：

• countDown：每调用一次countDown()，倒计时就会减少1，
• await：当倒计时到0时，await()方法就会停止阻塞

示例代码

public static void main(String[] args) throws InterruptedException {
        int N = 10;
        CountDownLatch latch = new CountDownLatch(N);
        CountDownLatch lock = new CountDownLatch(1);

        for (int i = 0; i < N; i++) {
            Thread.sleep(100L);
            new Thread(() -> {
                try {
                    lock.await();
                    System.out.println("---> start " + Thread.currentThread().getName());
                    Thread.sleep(1000L);
                    System.out.println("---> end " + Thread.currentThread().getName());
                    latch.countDown();
                } catch (Exception e) {
                    e.printStackTrace();
                }

            }).start();
        }
        lock.countDown();
        latch.await();
    }