java编程思想笔记-并发之CyclicBarrier

CyclicBarrier和CountDownLatch类似，可以让一组任务并行的工作，然后在下一个步骤之前等待，直至所有的任务完成，但是CountDownLatch只触发一次事件，而CyclicBarrier可以多次重用

示例：
赛马游戏

class Horse implements Runnable{
    private static int counter=0;
    //赛马id
    private final int id=counter++;
    //总步长
    private int strides=0;
    private static Random random=new Random(47);
    //栅栏
    private static CyclicBarrier barrier;
    public Horse(CyclicBarrier b){
        barrier=b;
    }
    public synchronized int getStrides() {
        return strides;
    }
    @Override
    public void run() {
        try {
            while (!Thread.interrupted()) {
                synchronized (this) {
                    strides+=random.nextInt(3);
                }
                barrier.await();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (BrokenBarrierException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    @Override
    public String toString() {
        return "House "+id+" ";
    }

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

}
public class HouseRace {
    static final int FINISH_LINE=75;
    private List<Horse>horses=new ArrayList<Horse>();
    private ExecutorService exec=Executors.newCachedThreadPool();
    private CyclicBarrier barrier;
    public HouseRace(int nHorses,final int pause){
        barrier=new CyclicBarrier(nHorses, new Runnable() {

            @Override
            public void run() {
                StringBuilder sb=new StringBuilder();
                for (int i = 0; i < FINISH_LINE; i++) {
                    sb.append("=");
                }
                System.out.println(sb);
                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) {
                    e.printStackTrace();
                }
            }
        });
        for (int i = 0; i < nHorses; i++) {
            Horse horse=new Horse(barrier);
            horses.add(horse);
            exec.execute(horse);
        }
    }
    public static void main(String[] args) {
        int nHorses=7;
        int pause=200;
        new HouseRace(nHorses, pause);
    }
}

所有的赛马线程每跑一次都被挂起，直到所有的赛马都处于栅栏处等待的时候，并且栅栏调用完barriarAction(CyclicBarrier初始化的第二个参数runnable)run()方法后，打破栅栏继续运行