java - 循环屏障异常处理

Question

我遇到循环屏障问题，请查看下面的代码 -

MeetingPoint1.java

public class MeetingPoint1 implements Runnable{

    @Override
    public void run() {
        System.out.println(" MeetingPoint1 one cleared... ");
    }

}

MeetingPoint2.java

public class MeetingPoint2 implements Runnable{

    @Override
    public void run() {
        System.out.println(" MeetingPoint Two cleared... ");
    }

}

VehicalRunnable.java

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

/**
 * @author chouhan_r
 *
 */
public class VehicleRunnable implements Runnable {

    private CyclicBarrier barrier1; 
    private CyclicBarrier barrier2;

    public VehicleRunnable(CyclicBarrier barrier1, CyclicBarrier barrier2) {
        this.barrier1 = barrier1;
        this.barrier2 = barrier2;
    }

    /* (non-Javadoc)
     * @see java.lang.Runnable#run()
     */
    @Override
    public void run() {
        try {
            Thread.sleep(1000);
            System.out.println(Thread.currentThread().getName() +" Waiting at Meeting Point 1");
            if(Thread.currentThread().getName().equalsIgnoreCase("Car")){
                throw new RuntimeException("something weird happened");
            }
            barrier1.await();
            Thread.sleep(1000);
            System.out.println(Thread.currentThread().getName() +" Waiting at Meeting Point 2");
            barrier2.await();

        } catch(BrokenBarrierException | RuntimeException | InterruptedException e){
            e.printStackTrace();
        }

    }

}

CyclicBarrierMain.java

import java.util.concurrent.CyclicBarrier;

/**
 * @author chouhan_r
 *
 */
public class CyclicBarrierMain {

    /**
     * @param args
     */
    public static void main(String[] args) {
        MeetingPoint1 meetingPoint1 = new MeetingPoint1();
        MeetingPoint2 meetingPoint2 = new MeetingPoint2();

        CyclicBarrier barrier1 = new CyclicBarrier(3, meetingPoint1);
        CyclicBarrier barrier2 = new CyclicBarrier(3, meetingPoint2);

        VehicleRunnable car = new VehicleRunnable(barrier1, barrier2);
        VehicleRunnable bike = new VehicleRunnable(barrier1, barrier2);
        VehicleRunnable bus= new VehicleRunnable(barrier1, barrier2);
        new Thread(car,"Car").start();
        new Thread(bike,"Bike").start();
        new Thread(bus,"Bus").start();
    }

}

当线程抛出一些异常时，所有其他线程都在屏障 1 处等待，有什么方法可以运行等待线程直到屏障 2 吗？将barrier.await()方法放在finally block 中是不是一个更好的主意？

Answer 1

您正在使用计数器 3 创建循环屏障。其中两个线程能够调用 Barrier1.await()；因此等待计数器为零，以便它们可以继续进行，但第三个线程无法调用barrier1.await()，因为您在调用barrier.await()之前已显式抛出异常。因此计数器不会为零，并且所有其他线程将卡在barrier1.await()处。

如果你想让所有其他线程继续进行，你必须在抛出异常之前再次调用barrier.await()，就像在这个 block 中一样。

 if(Thread.currentThread().getName().equalsIgnoreCase("Car")){
                barrier1.await(); // call here
                throw new RuntimeException("something weird happened");
   }