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
