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