public class YuanThread {

private Boolean flag = true;

public void refresh() {
    System.out.println(Thread.currentThread().getName() + "refresh flag");
    flag = false;
}

public void forS() {
    System.out.println(Thread.currentThread().getName() + "开始执行");

    int i = 0;
    while (flag) {
        i++;
        // System.out.println();
        // sleep(100000);
        // sleep(1000);
    }
    System.out.println(Thread.currentThread().getName() + "跳出循环i=" + i);
}

public static void main(String[] args) {
    YuanThread yuanThread = new YuanThread();
    new Thread(() -> {
        yuanThread.forS();
    }, "thread1").start();


    try {
        Thread.sleep(2000);
        new Thread(() -> {
            yuanThread.refresh();
        }, "thread2").start();


    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

public static void sleep(long interval) {
    long start = System.nanoTime();
    long end;
    do {
        end = System.nanoTime();
    } while (start + interval > end);
}

}

i++ 下面增加不同耗时的操作，则有可能使循环结束。为什么thread1没有及时获取到thread2修改过的值呢？thread1的工作内存中的flag何时才能被刷新？