LeetCode做题解析-多线程部分（1）

class Foo {
　　　private Semaphore seam_first_two = new Semaphore(0);  // 同一时间只有0个线程能访问，意味着锁定
    
     private Semaphore seam_two_three = new Semaphore(0);
    
    public Foo() {
    }

    public void first(Runnable printFirst) throws InterruptedException {
        // 没有阻塞，直接执行了
　　　　 printFirst.run();
　　　　 // 释放一个执行许可seam_first_two
        seam_first_two.release();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        // 需要等待seam_first_two释放
        seam_first_two.acquire();
        printSecond.run();
　　　　　// 释放一个执行许可seam_two_three
        seam_two_three.release();
    }

    public void third(Runnable printThird) throws InterruptedException {
        // 需要等待seam_two_three释放
        seam_two_three.acquire();
        printThird.run();
    }
}