volatile可见性

总线(MESI缓存一致性协议)

read

load

initflag=false

线程2

write

store(存储)

工作内存

initFlag=false

initFlag=true

lock

主内存

assign(赋值)

public class VolatileVisibilityTest {    private static volatile boolean initFlag = false;    public static void main(String[] args) throws InterruptedException{        new Thread(new Runnable(){            @Override            public void run(){                System.out.println(\"waiting data...\");                while(!initFlag){                }                System.out.println(\"========success!\");            }        }).start();        Thread.sleep(2000);        new Thread(new Runnable() {            @Override            public void run() {                prepareData();            }        }).start();    }    public static void prepareData(){        System.out.println(\"start data...\");        initFlag = true;        System.out.println(\"data end...\");    }} 

当cpu总线嗅探机制(监听)察觉到总线发生变化时，工作内存中nitFlag=false失效且cpu重新read和load主内存为了防止cpu总线嗅探机制(监听)将还未write的数据重新写入工作内存中，会在store(存储)之前加锁(lock)且在write之后解锁(unlock)，这样线程1就不会因为重新读取的是旧的数据而陷入死循环

use

initflag=false-->true

线程1(执行引擎)initFlag

initFlag=false-->true

unlock

volatile可见性

CPU

cpu总线嗅探机制(监听)