java 并发编程-CyclicBarrier

功能描述

CyclicBarrier（回环栅栏或循环屏障），是Java并发库中的一个同步工具，通过它可以实现让一组线程等待至某个状态（屏障点）之后再全部同时执行。叫做回环是因为当所有等待线程都被释放以后，CyclicBarrier可以被重用。与CountDownLatch的区别是CyclicBarrier是可以循环使用的。CyclicBarrier使用ReentrantLock+Condition实现。

API

1. await() 每个线程调用await方法告诉CyclicBarrier我已经到达了屏障，然后当前线程被阻塞。所有的线程全部调用await()方法时，这些线程不再阻塞
2. await(long timeout, TimeUnit unit)

使用示例

public class Main {
    public static void main(String[] args) throws BrokenBarrierException, InterruptedException {
        final CyclicBarrier barrier = new CyclicBarrier(11);

        for(int i = 0; i < 10; i++) {
            new Thread(new Tourist(i, barrier)).start();
        }
        barrier.await();
        System.out.println("所有人都上了车");
        barrier.await();
        System.out.println("所有人都下了车");
    }

    private static class Tourist implements Runnable {

        private final int touristID;
        private final CyclicBarrier barrier;

        public Tourist(int id, CyclicBarrier barrier) {
            this.touristID = id;
            this.barrier = barrier;
        }
        @Override
        public void run() {
            System.out.printf("游客%d乘坐旅游大巴\n", touristID);

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }

            try {
                System.out.printf("游客%d上车，等别人上车\n", touristID);
                barrier.await();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            } catch (BrokenBarrierException e) {
                throw new RuntimeException(e);
            }

            System.out.printf("游客%d到达目的地\n", touristID);

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }

            try {
                System.out.printf("游客%d下车，等别人下车\n", touristID);
                barrier.await();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            } catch (BrokenBarrierException e) {
                throw new RuntimeException(e);
            }
        }
    }
}