1 package com.duyang.thread.basic.basethread;

 2

 3 /**

 4  * @author ：jiaolian

 5  * @date ：Created in 2020-12-16 14:02

 6  * @description：线程不安全分析

 7  * @modified By：

 8  * 公众号:叫练

 9  */

10 public class ThreadUnsafe {

11

12     public static void main(String[] args) {

13         Thread task = new Task();

14         Thread threadA = new Thread(task,"A");

15         Thread threadB = new Thread(task,"B");

16         Thread threadC = new Thread(task,"C");

17         Thread threadD = new Thread(task,"D");

18         Thread threadE = new Thread(task,"E");

19         threadA.start();

20         threadB.start();

21         threadC.start();

22         threadD.start();

23         threadE.start();

24     }

25

26     private static class Task extends Thread {

27

28         int count = 5;

29         @Override

30         public void run() {

31             /**

32              * jvm分3步骤;

33              * 1.获取count(从主内存获取值)

34              * 2.count减1(在各自寄存器完成)

35              * 3.保存count(刷新到主内存)

36              *

37              * 说下可能执行的过程...

38              * A线程获取cpu的count值为5，A线程先减去1，保存count值为4刷新到主内存,此时还没有执行System.out.println count

39              * 切换到B线程，此时B线程的count值为4，因为B线程是从主内存取的，B线程count值减去1为3，此时刷新到主内存，主内存值变为3

40              * 切换到A线程，执行System.out.println count=3

41              * 切换到B线程，执行System.out.println count=3

42              * 情况就是这样的

43              *

44              */

45             count--;

46             System.out.println(Thread.currentThread().getName() + " "+count);

47         }

48     }

49 }