java.util.concurrent 之三： 出发--等待--汇合--再出发
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。
package test;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{// 徒步需要的時間private static int[] timeWalk = { 5, 8, 15, 15, 10 };// 自駕遊private static int[] timeSelf = { 1, 3, 4, 4, 5 };// 旅遊大巴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){// 三個旅行團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(); }}21:47:18: SelfTour Reached Shenzhen21:47:19: BusTour Reached Shenzhen21:47:22: WalkTour Reached Shenzhen21:47:25: SelfTour Reached Guangzhou21:47:26: BusTour Reached Guangzhou21:47:30: WalkTour Reached Guangzhou21:47:34: SelfTour Reached Shaoguan21:47:36: BusTour Reached Shaoguan21:47:45: WalkTour Reached Shaoguan21:47:49: SelfTour Reached Changsha21:47:51: BusTour Reached Changsha21:48:00: WalkTour Reached Changsha21:48:05: SelfTour Reached Wuhan21:48:07: BusTour Reached Wuhan21:48:10: WalkTour Reached Wuhan