java内存模型（JMM）

探秘volatile加不加的区别

read

工作内存

线程2

use

flag=false

load

flag=true

主内存

package com.john.study.jmm;public class JavaMemoryModel01Test { private static boolean flag =false; public static void main(String[] args) throws InterruptedException { new Thread(()->{ System.out.println(\"waiting data...\"); while (!flag){ } System.out.println(\"=========success\"); }).start(); Thread.sleep(2000L); new Thread(()->modefyFlag()).start(); } public static void modefyFlag() { System.out.println(\"prepare data\"); flag=true; System.out.println(\"prepare data end...\"); }}

init Flag=false

assign

flag=false---> flag=true

静态变量不加volatile关键字，某一线程修改了从主存的数据其他线程不可见，

CPU

加volatile关键字

线程1

总线

总结：加了volatile关键字后，又线程修改，其他线程能够立马感知到

write

总线（缓存一致性协议）

不加volatile关键字

总线嗅探机制（监听）

package com.john.study.jmm;public class JavaMemoryModel01Test {    private static volatile boolean flag =false;    public static void main(String[] args) throws InterruptedException {        new Thread(()->{            System.out.println(\"waiting data...\");            while (!flag){            }            System.out.println(\"=========success\");        }).start();        Thread.sleep(2000L);        new Thread(()->modefyFlag()).start();    }    public static void modefyFlag() {        System.out.println(\"prepare data\");        flag=true;        System.out.println(\"prepare data end...\");    }} 

store