java.util.concurrent.CountDownLa

CountDownLatch: .await方法 用到共享锁 getState 是一个计数器，当计数器大于0获取共享锁，若等于0不需要加锁
CountDownLatch：内部有一个sync同步工具集成了AQS

public class CountDownLatchDemo {
    public static void main(String[] args) throws InterruptedException {
        //计算器为3
        CountDownLatch countDownLatch = new CountDownLatch(3);

        new Thread(() -> {
            //计算器-1
            countDownLatch.countDown();
        }).start();

        new Thread(() -> {
            //计算器-1
            countDownLatch.countDown();
        }).start();

        new Thread(() -> {
            //计算器-1
            countDownLatch.countDown();
        }).start();

        //使用场景：1、并行请求，比如100个线程同时进行，可以使用countDown结合await阻塞处理
        //2、
        countDownLatch.await();//主线程阻塞，直到计算器变为0
        System.out.println("完毕");
    }
}

运行结果

完毕

Process finished with exit code 0