public static void main(String[] args) throws Exception{
        CountDownLatch latch = new CountDownLatch(2);

        new Thread(()->{
            try {
                Thread.sleep(2000);
                System.out.println("线程1准备执行 countDown 操作");
                latch.countDown();
            }catch (Exception e){
                e.printStackTrace();
            }
        }).start();

        new Thread(()->{
            try {
                Thread.sleep(2000);
                System.out.println("线程2准备执行 countDown 操作");
                latch.countDown();
            }catch (Exception e){
                e.printStackTrace();
            }
        }).start();

        System.out.println("main() 线程准备执行 await");
        latch.await();
        System.out.println("success");
    }