2020-04-08（1114. 按序打印*）

难度 简单
低速通过，涉及线程的还不是很熟，后面需要系统看下线程的。
执行用时 :18 ms, 在所有 Java 提交中击败了6.70%的用户
内存消耗 :39.1 MB, 在所有 Java 提交中击败了5.09%的用户

int mark = 0;
    Object lock = new Object();
    public Foo() {
    }

    public void first(Runnable printFirst) throws InterruptedException {
        synchronized(lock){
            // printFirst.run() outputs "first". Do not change or remove this line.
            printFirst.run();
            mark = 1;
            lock.notifyAll();
        }
    }

    public void second(Runnable printSecond) throws InterruptedException {
        synchronized(lock){
            while(mark != 1){
                lock.wait();
            }
            // printSecond.run() outputs "second". Do not change or remove this line.
            printSecond.run();
            mark = 2;
            lock.notifyAll();
        }

    }

    public void third(Runnable printThird) throws InterruptedException {
        synchronized(lock){
            while(mark != 2){   
                lock.wait();
            }
            // printThird.run() outputs "third". Do not change or remove this line.
            printThird.run();
            lock.notifyAll();
        }
    }