java CyclicBarrier 没有被重置破坏

Question

我正在尝试通过在启动(等待)几个方(线程)的过程中重置 cyclicbarrier 来测试 BrokenBarrierException，请在下面找到相同的示例代码。

用户类:

public class User implements Runnable {
    
    private final String name;
    private final CyclicBarrier cb;
    
    public User(String name, CyclicBarrier cb) {
        this.name = name;
        this.cb = cb;
    }

    @Override
    public void run() {
        System.out.println(name+" user started !!!! ");
        try {
            cb.await();
        } catch (InterruptedException | BrokenBarrierException e) {
            System.out.println(e);
            e.printStackTrace();
        }
    }
}

CyclicBarrierTest 类:

public class CyclicBarrierTest {

    public static void main(String[] args) {
        CyclicBarrier barrier = new CyclicBarrier(5);
        
        User user1 = new User("USER1", barrier);
        new Thread(user1).start();
        
        User user2 = new User("USER2", barrier);
        new Thread(user2).start();
        
        //Expected users are 5, but only 2 user threads started so far 
        // and resetting below which should throw barrier broken exception

        barrier.reset();
        
        if(barrier.isBroken()) {
            System.out.println("Barrier broken ");
        }
    }
}

所以，在运行上面的 main() 之后，我可以得到任何异常，而且“Barrier broken”也没有打印出来。线程只是在等待。

I have referred the CyclicBarrier API below link:

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/CyclicBarrier.html

public void reset():

Resets the barrier to its initial state. If anyparties are currently waiting at the barrier, they will return with aBrokenBarrierException.

但根据 API 描述，我的上述代码似乎无法正常工作，那么我的上述代码有什么问题，为什么它没有抛出 BrokenBarrierException ？

你能帮忙吗？

Answer 1

如果你想抛出异常，你必须确保 barrier.reset(); 在 cb.await(); 之后执行，但是这里 System. out.println(name+"user started !!!! "); 是一个非常昂贵的语句，它使得 barrier.reset(); 执行得太早，你可以在之前添加一个 sleep 语句barrier.reset(); ，比如 Thread.sleep(100);。

isBroken 的文档:

true if one or more parties broke out of this barrier due to interruption or timeout since construction or the last reset, or a barrier action failed due to an exception; false otherwise.

如果你想把它当成破烂的，你可以为当事人做点什么。您需要删除 reset 以使线程等待。

public class User implements Runnable {

    private final String name;
    private final CyclicBarrier cb;

    public User(String name, CyclicBarrier cb) {
        this.name = name;
        this.cb = cb;
    }

    @Override
    public void run() {
        System.out.println(name+" user started !!!! ");
        try {
            cb.await(1,TimeUnit.SECONDS);
        } catch (InterruptedException | BrokenBarrierException e) {
            e.printStackTrace();
        } catch (TimeoutException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
        System.out.println(name+" user ended !!!! ");
    }
}


public class CyclicBarrierTest {

    public static void main(String[] args) throws Exception {
        CyclicBarrier barrier = new CyclicBarrier(5);

        User user1 = new User("USER1", barrier);
        new Thread(user1).start();

        User user2 = new User("USER2", barrier);
        new Thread(user2).start();


        //Expected users are 5, but only 2 user threads started so far 
        // and resetting below which should throw barrier broken exception
        Thread.sleep(100);
//        barrier.reset();
        Thread.sleep(1100);
        if(barrier.isBroken()) {
            System.out.println("Barrier broken ");
        }
    }
}