java CyclicBarrier

使用情況：你希望建立一組任務，他們並行執行，然後再進行下一個步驟之前等待，直到所有任務都完成

下面是一個賽馬的例子，挺有意思的（java程式設計思想）

import java.util.concurrent.*;
import java.util.*;

public class Horse implements Runnable {

	private static int counter=0;
	private final int id=counter++;
	private int strides=0;
	private static Random rand=new Random(47);
	private static CyclicBarrier barrier;
	public Horse(CyclicBarrier barrier){
		this.barrier=barrier;
	}
	public synchronized int getStrides(){
		return strides;
	}
	@Override
	public void run() {
		// TODO Auto-generated method stub
		try{
			while(!Thread.interrupted()){
				synchronized(this){
					strides+=rand.nextInt(3);
				}
				barrier.await();
			}
		}
		catch(InterruptedException e){}
		catch(BrokenBarrierException e){
			throw new RuntimeException(e);
		}

	}
	public String toString(){
		return "Horse "+id+" ";
	}
	public String tracks(){
		StringBuilder s=new StringBuilder();
		for(int i=0;i<getStrides();i++){
			s.append("*");
		}
		s.append(id);
		return s.toString();
	}
}

import java.util.concurrent.*;
import java.util.*;

public class HorseRace {
	public static final int FINISH_LINE=75;
	private List<Horse> horses =new ArrayList<Horse>();
	private ExecutorService exec=Executors.newCachedThreadPool();
	private CyclicBarrier barrier;
	public HorseRace(int nHorses,final int pause){
		barrier=new CyclicBarrier(nHorses,new Runnable(){
			public void run(){
				StringBuilder  s=new StringBuilder();
				for(int i=0;i<FINISH_LINE;i++)
					s.append("=");
				System.out.println(s);
				for(Horse horse:horses)
					System.out.println(horse.tracks());
				for(Horse horse:horses){
					if(horse.getStrides()>=FINISH_LINE){
						System.out.println(horse+" won!");
						exec.shutdownNow();
						return;
					}
					try{
						TimeUnit.MILLISECONDS.sleep(pause);
					}catch(InterruptedException e){
						System.out.println("barrier-action sleep interrupted");
					}
				}
			}
		});
		for(int i=0;i<nHorses;i++){
			Horse horse=new Horse(barrier);
			horses.add(horse);
			exec.execute(horse);
		}
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int nHorses=7;
		int pause=200;
		new HorseRace(nHorses,pause);

	}

}