JAVA 同步器CountDownLatch CyclicBarrier

CountDownLatch

可以实现类似计数器的功能，一般用于某个线程等待若干个其他线程执行完任务之后，它才执行

CyclicBarrier

一组线程互相等待至某个状态，然后这一组线程再同时执行

• CountDownLatch例子

import java.util.concurrent.CountDownLatch;

public class JavaCountDownLatch {

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(5);
        for (int i = 0; i < 5; i++)
            new JavaCountDownLatch.Student(countDownLatch, i).start();
        System.out.println("等待所有同学到达");
        countDownLatch.await();
        System.out.println("所有同学到达目的地");

    }

    static class Student extends Thread {
        private CountDownLatch countDownLatch;
        private int id;

        public Student(CountDownLatch countDownLatch, int id) {
            this.countDownLatch = countDownLatch;
            this.id = id;
        }

        public void run() {
            try {
                System.out.println("student " + id + "出发");
                Thread.sleep(3000);
                System.out.println("student " + id + "到达");
                countDownLatch.countDown();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

执行结果：
student 0出发
等待所有同学到达
student 2出发
student 4出发
student 1出发
student 3出发
student 0到达
student 2到达
student 4到达
student 1到达
student 3到达
所有同学到达目的地

• CyclicBarrier例子

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class JavaCyclicBarrier {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        CyclicBarrier cyclicBarrier = new CyclicBarrier(5);
        for (int i = 0; i < 5; i++)
            new JavaCyclicBarrier.Student(cyclicBarrier, i).start();
    }

    static class Student extends Thread {
        private CyclicBarrier cyclicBarrier;
        private int id;
        public Student(CyclicBarrier cyclicBarrier, int id) {
            this.cyclicBarrier = cyclicBarrier;
            this.id = id;
        }
        public void run() {
            try {
                System.out.println("student " + id + "出发");
                Thread.sleep(3000);
                System.out.println("student " + id + "到达,等待其他同学");
                cyclicBarrier.await();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("所有同学到达目的地");
        }
    }
}

执行结果：
student 1出发
student 3出发
student 0出发
student 2出发
student 4出发
student 3到达,等待其他同学
student 1到达,等待其他同学
student 0到达,等待其他同学
student 2到达,等待其他同学
student 4到达,等待其他同学
所有同学到达目的地
所有同学到达目的地
所有同学到达目的地
所有同学到达目的地
所有同学到达目的地

参考资料

• http://www.cnblogs.com/dolphin0520/p/3920397.html
• http://blog.youkuaiyun.com/mazhimazh/article/details/19190241