Java多线程入门——抢票问题

Question

public class FinalAttack {
    public static void main(String[] args) {
        buyT station =new buyT();

        new Thread(station,"a").start();
        new Thread(station,"b").start();
        new Thread(station,"c").start();
    }
}
class buyT implements Runnable{

    private int tnum=10;
    boolean flag=true;
    @Override

    public void run() {
        while (flag){
            try {
                buy();
                //Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    private synchronized void buy() throws InterruptedException {
        if(tnum<=0){
            flag=false;
            return;
        }
        Thread.sleep(1000);
        System.out.println(Thread.currentThread().getName()+"拿到"+tnum--);

    }
}

上方代码运行结果为

我想实现的效果是模拟抢票：

为什么把sleep的位置换一下就可以实现了？

public class FinalAttack {
    public static void main(String[] args) {
        buyT station =new buyT();

        new Thread(station,"a").start();
        new Thread(station,"b").start();
        new Thread(station,"c").start();
    }
}
class buyT implements Runnable{

    private int tnum=10;
    boolean flag=true;
    @Override

    public void run() {
        while (flag){
            try {
                buy();
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    private synchronized void buy() throws InterruptedException {
        if(tnum<=0){
            flag=false;
            return;
        }
        System.out.println(Thread.currentThread().getName()+"拿到"+tnum--);

    }
}

希望能得到一个便于理解的回答，谢谢。

Answer 1

sleep 放在同步函数没有意义，只是降低了程序的性能，因为同步函数当前线程没有运行完，别的线程是进不去的，而把sleep放在run里面，才能模拟抢票的情况。sleep的意思是当前线程休眠，休眠的时候，别的用户就可以同时进来抢票。