障碍循环(Cyclic Barriers)

在实际应用中，有时候需要多个线程同时工作以完成同一件事情，而且在完成过程中，往往会等待其他线程都完成某一阶段后再执行，等所有线程都到达某一个阶段后再统一执行。

比如有几个旅行团需要途经深圳、广州、韶关、长沙最后到达武汉。旅行团中有自驾游的，有徒步的，有乘坐旅游大巴的；这些旅行团同时出发，并且每到一个目的地，都要等待其他旅行团到达此地后再同时出发，直到都到达终点站武汉。

这时候CyclicBarrier就可以派上用场。CyclicBarrier最重要的属性就是参与者个数，另外最要方法是await()。当所有线程都调用了await()后，就表示这些线程都可以继续执行，否则就会等待。

 

import java.text.SimpleDateFormat;     
import java.util.Date;     
import java.util.concurrent.BrokenBarrierException;     
import java.util.concurrent.CyclicBarrier;     
import java.util.concurrent.ExecutorService;     
import java.util.concurrent.Executors;     
    
public class TestCyclicBarrier {     
    // 徒步需要的时间: Shenzhen, Guangzhou, Shaoguan, Changsha, Wuhan     
    private static int[] timeWalk = { 5, 8, 15, 15, 10 };     
    // 自驾游     
    private static int[] timeSelf = { 1, 3, 4, 4, 5 };     
    // 旅游大巴     
    private static int[] timeBus = { 2, 4, 6, 6, 7 };     
    
    static String now() {     
        SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");     
        return sdf.format(new Date()) + ": ";     
    }     
    
    static class Tour implements Runnable {     
        private int[] times;     
        private CyclicBarrier barrier;     
        private String tourName;     
    
        public Tour(CyclicBarrier barrier, String tourName, int[] times) {     
            this.times = times;     
            this.tourName = tourName;     
            this.barrier = barrier;     
        }     
    
        public void run() {     
            try {     
                Thread.sleep(times[0] * 1000);     
                System.out.println(now() + tourName + " Reached Shenzhen");     
                barrier.await();     
                Thread.sleep(times[1] * 1000);     
                System.out.println(now() + tourName + " Reached Guangzhou");     
                barrier.await();     
                Thread.sleep(times[2] * 1000);     
                System.out.println(now() + tourName + " Reached Shaoguan");     
                barrier.await();     
                Thread.sleep(times[3] * 1000);     
                System.out.println(now() + tourName + " Reached Changsha");     
                barrier.await();     
                Thread.sleep(times[4] * 1000);     
                System.out.println(now() + tourName + " Reached Wuhan");     
                barrier.await();     
            } catch (InterruptedException e) {     
            } catch (BrokenBarrierException e) {     
            }     
        }     
    }     
    
    public static void main(String[] args) {     
        // 三个旅行团     
        CyclicBarrier barrier = new CyclicBarrier(3);     
        ExecutorService exec = Executors.newFixedThreadPool(3);     
        exec.submit(new Tour(barrier, "WalkTour", timeWalk));     
        exec.submit(new Tour(barrier, "SelfTour", timeSelf));     
        exec.submit(new Tour(barrier, "BusTour", timeBus));     
        exec.shutdown();     
    }     
}   

 

本文转自：http://blog.csdn.net/injuer/archive/2010/04/03/5447538.aspx