Question

public class StopMultiThread {
    private static boolean stopRequested;

    public static void main(String[] args) throws InterruptedException {
        int testNum = 100;
        List<Boolean> result = new ArrayList<>(testNum);
        CountDownLatch countDownLatch = new CountDownLatch(testNum);
        for (int i = 0; i < testNum; i++) {
            int copy = i;
            Thread backgroundThread = new Thread(new Runnable() {
                @Override
                public void run() {
                    long beginTime = System.currentTimeMillis();
                    int j = 0;
                    while (!stopRequested) {
//                        j++;
                        System.out.println("brokenStopMultiThread " + copy + " " + j++);
                    }
                    long runTime = System.currentTimeMillis() - beginTime;
                    System.out.println("brokenStopMultiThread " + copy + " run " + runTime);
                    result.add(runTime < 1500);
                    countDownLatch.countDown();
                }
            });
            backgroundThread.start();
        }
        TimeUnit.SECONDS.sleep(1);
        stopRequested = true;
        countDownLatch.await();
        System.out.println("result:" + result);
        int expectedTimes = 0;
        for (Boolean b : result)
            if (b)
                expectedTimes++;
        System.out.println("expectedTimes:" + expectedTimes + ", brokenTimes:" + (result.size() - expectedTimes));
    }
}

环境

java版“1.8.0_77”

Java（TM）SE运行时环境（版本1.8.0_77-b03）

Java HotSpot（TM）64位服务器VM（内置25.77-b03，混合模式）

上面的代码可以正常停止线程，但下面的代码不能，为什么？

while (!stopRequested) {
    j++;
    // System.out.println("brokenStopMultiThread " + copy + " " + j++);
}

测试5次

代码A将导致

expectedTimes：23，brokenTimes：977

expectedTimes：45，brokenTimes：955

expectedTimes：174，brokenTimes：825

expectedTimes：207，brokenTimes：793

expectedTimes：175，brokenTimes：825

代码A

while (!stopRequested) {
    try {
        TimeUnit.MILLISECONDS.sleep(10);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    j++;
//  System.out.println("brokenStopMultiThread " + copy + " " + j++);
}

代码B将导致

expectedTimes：1000，brokenTimes：0

expectedTimes：999，brokenTimes：0

expectedTimes：1000，brokenTimes：0

代码B

while (!stopRequested) {
    /*try {
        TimeUnit.MILLISECONDS.sleep(10);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    j++;*/
    System.out.println("brokenStopMultiThread " + copy + " " + j++);
}

所有线程都以不同的runTime停止，也许在jdk8上不会轻易发生活动失败

关于有效的java 2 char 10项目66

0 个答案: