有如下代码
public class VolatileSortTest {
private static int a = 0;
private static int b = 0;
private static int c = 0;
private static volatile int d = 0;
private static int e = 0;
private static int f = 0;
private static int g = 0;
private static int h = 0;
public static void main(String[] args) throws InterruptedException {
for (int i = 0; i < 500000; i++) {
//join可以保证线程a b都执行完成之后,再继续下一次循环
ThreadA threadA = new ThreadA();
ThreadB threadB = new ThreadB();
threadA.start();
threadB.start();
threadA.join();
threadB.join();
//清空数据,便于测试
a = 0;
b = 0;
c = 0;
d = 0;
e = 0;
f = 0;
g = 0;
h = 0;
}
}
static class ThreadA extends Thread {
@Override
public void run() {
a = 1;
b = 1;
c = 1;
d = 1;
e = 1;
f = 1;
g = 1;
h = 1;
}
}
static class ThreadB extends Thread {
@Override
public void run() {
if (b == 1 && a == 0) {
System.out.println("b=1");
}
if (c == 1 && (a == 0 || b == 0)) {
System.out.println("c=1");
}
if (d == 1 && (a == 0 || b == 0 || c == 0)) {
System.out.println("d=1");
}
if (e == 1 && (a == 0 || b == 0 || c == 0 )) {
System.out.println("e=1");
}
if (f == 1 && (a == 0 || b == 0 || c == 0 )) {
System.out.println("f=1");
}
if (g == 1 && (a == 0 || b == 0 || c == 0 )) {
System.out.println("g=1");
}
if (h == 1 && (a == 0 || b == 0 || c == 0 )) {
System.out.println("h=1");
}
}
}
}
我想要测试 volatile 关键词的禁止指令重排序,但是结果很出人意外,依然会打印出一些"g=1","f=1","e=1" 的字样,已经把d 添加了关键字 volatile,在操作d的时候会添加内存屏障,为什么 g = 1 的时候,a,b,c还有存在为0的现象?
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