Java并发编程之CountDownLatch原理详解

public static void main(String[] args) throws InterruptedException {
    //内部sync同步器的state值设为3
    CountDownLatch countDownLatch = new CountDownLatch(3);

    for (int i = 1;i <= 3;i++) {
        new Thread(() -> {
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                System.out.println("目标代码块运行完毕");
                //每调用一次countDown()内部调用releaseShared(1)都会使state值减一
                countDownLatch.countDown();
            }
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("线程结束");
        }).start();
    }
    System.out.println("所有线程已启动");
    //主线程调用await()方法后就会进入阻塞，直到所有线程调用了countDown()使state值被减为0，或者主线程被中断，才会从阻塞返回
    countDownLatch.await();
    System.out.println("所有线程目标代码块已运行完毕");
}