Semaphore和CountDownLatch

1、 Semaphore信号量共享锁，创建锁时传入的参数代表一次放行几个线程。下边的例子模拟了排队进厕所的场景，保安一次放行2个人进去蹲坑

private void semDemo() {
        Semaphore semaphore = new Semaphore(2);
        for (int i = 0; i < 8; i++) {
            new Thread(() -> {
                try {
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName() + "开始蹲坑");
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();
                }
            }, "编号" + i).start();
        }
    }

2、 CountDownLatch，另外一种共享锁，下边的例子模拟了上船的场景，一条船只能坐五个人，当人数够了五个之后就开船

private void CountDownDemo() throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(5);
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 10; i++) {
            int finalI = i;
            executorService.execute(() -> {
                try {
                    Random random = new Random();
                    int a = random.nextInt(10000);
                    Thread.sleep(a);
                    if(countDownLatch.getCount() <= 0){
                        System.out.println("乘客" + finalI + "未上船，因为船已经满员开走");
                    } else {
                        System.out.println("乘客" + finalI + "已上船，耗时" + a + "毫秒");
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    countDownLatch.countDown();
                }
            });
        }
        countDownLatch.await();
        System.out.println("船已经满员，开船");
        executorService.shutdown();
    }