禁用CPU 缓存

告诉编译器，对这个变量的读写，不能使用 CPU 缓存，必须从内存中读取或者写入

/*** TODO 在此写上类的相关说明.<br>* @author gqltt<br>* @version 1.0.0 2020年4月8日<br>* @see * @since JDK 1.5.0*/
public class VolatileExample {int x = 0;volatile boolean b = false;public void writer() {x = 42;b = true;}public void reader() {if(b) {System.out.println("x=" + x);}}/*** @param args*/public static void main(String[] args) {VolatileExample example = new VolatileExample();Thread th1 = new Thread(()->{CommonUtil.sleep(100);example.writer();});Thread th2 = new Thread(()->{CommonUtil.sleep(300);example.reader();});th1.start();th2.start();try {th1.join();th2.join();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

 

1、根据规则1，x=42 Happens-Before v=true
2、根据规则2，写变量v=true Happens-Before 读变量 v=true
3、根据规则3，x=42 Happens-Before 读变量 v=true