java多线程-竞态条件的形成模拟，锁的使用，volatile关键字的使用

很简单的一次尝试。

售票的机器类

public class TicketSell implements Runnable{
    private volatile int number = 10; //第四次尝试去掉了volatile


    @Override
    public void run() {
        while (number > 0) {
            sold();
        }
    }

    public synchronized void  sold(){  //只有第三次的时候加了synchronized
        if (number > 0) {
            System.out.println(Thread.currentThread().getName()+"sold "+number);
            number--;
        }
    }

}

售票主函数

public class TicketMain {
    public static void main(String[] args) {
        TicketSell thread = new TicketSell();
        TicketSell thread2 = new TicketSell();
        Thread t1 = new Thread(thread);
        Thread t2 = new Thread(thread);
        t1.setName("t1");
        t2.setName("t2");
        t1.start();
        t2.start();
    }
}

第一次：

使用thread和thread1对象两个线程分别跑起来，把thread对象和thread1对象传进去，相当于两个机器分别卖各自的票，各自有10张票

运行结果：

t2 sold 10
t2 sold 9
t1 sold 10
t2 sold 8
t1 sold 9
t2 sold 7
t1 sold 8
t2 sold 6
t1 sold 7
t2 sold 5
t1 sold 6
t1 sold 5
t1 sold 4
t1 sold 3
t1 sold 2
t1 sold 1
t2 sold 4
t2 sold 3
t2 sold 2
t2 sold 1


Process finished with exit code 0

互相不受影响，按照10-1顺序减下来

第二次：

然后将thread都传进t1和t2，类似于一个售票机分身两个（这样好理解？）然后类似于同时工作

运行结果是这样的（可能还有很神奇的负数或者0出现，因为出现了竞态条件）

t2 sold 10
t1 sold 10
t2 sold 9
t1 sold 8
t2 sold 7
t1 sold 6
t2 sold 5
t2 sold 3
t1 sold 4
t2 sold 2
t1 sold 1

Process finished with exit code 0

第三次：

加上了synchronized之后，就实现了正常的效果

t1 sold 10
t1 sold 9
t1 sold 8
t1 sold 7
t1 sold 6
t2 sold 5
t2 sold 4
t2 sold 3
t2 sold 2
t2 sold 1

Process finished with exit code 0

第四次：

volatile

    作用：用于状态的存放，共享，确保变量的更新操作通知到其他线程。 
  

前面几次都是在volatile变量使得可见性得到确保然后不会出现这样的情况

t2 sold 10
t1 sold 10
t2 sold 9
t2 sold 7
t2 sold 6
t2 sold 5
t2 sold 4
t2 sold 3
t2 sold 2
t2 sold 1
t1 sold 8

Process finished with exit code 0

t1最后还在卖8号票说明可见性出现了问题。

java多线程-竞态条件的形成模拟，锁的使用，volatile关键字的使用

猜你喜欢