public class OutOfOrderExecution {
    private static int x = 0, y = 0;
    private static int a = 0, b = 0;
    private static CountDownLatch countDownLatch = new CountDownLatch(1);

    public static void main(String[] args) throws InterruptedException {
        int i = 0;
        for (; ; ) {
            i++;
            x = 0;
            y = 0;
            a = 0;
            b = 0;

            Thread one = new Thread(() -> {
                try {
                    countDownLatch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                a = 1;
                x = b;
            });

            Thread two = new Thread(() -> {
                try {
                    countDownLatch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                b = 1;
                y = a;
            });

            two.start();
            one.start();
            countDownLatch.countDown();
            one.join();
            two.join();
            System.out.println("第" + i + "次 x = " + x + ", y = " + y);
            if (x == 0 && y == 0) {
                break;
            }
        }
    }
}

对于课程中关于重排序举的这个例子，由于是在两个线程中对于共享变量的操作，这种操作是线程不安全的，即使当两个线程运行完成，x = 1,y = 1,那么这时主存中的x和y还未得到更新，则会出现x = 0,y = 0的情况，我的理解是这种并非发生了指令重排序。

麻烦解答一下？