java Concurrent包中的CountDownLatch

Java CountDownLatch学习记录

CountDownLatch顾名思义通过计数的下降来触发被其标识的线程，可以通过初始话一个CountDownLatch来设置需要等待的线程，如CountDownLatch begin = new CountDownLatch(2); 也就是你可以线程中使用begin.await（）来使当前线程阻塞，只有当begin的个数计数变成0，之前设置await的线程才能继续往下面跑! 但是这个计数器的值不可以重置，也就是他初始化一次只能使用一次；如果需要重置可以使用CyclicBarrier。

下面是一个具体的例子（网上取的）：

package json;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Test {
    public static void main(String args[]) throws InterruptedException {

        final CountDownLatch begin = new CountDownLatch(1);

        // 结束的倒数锁

        final CountDownLatch end = new CountDownLatch(10);

        // 十名选手

        final ExecutorService exec = Executors.newFixedThreadPool(10);

        for (int index = 0; index < 10; index++) {
            final int NO = index + 1;
            Runnable run = new Runnable() {
                public void run() {
                    try {
                        begin.await();// 一直阻塞
                        Thread.sleep((long) (Math.random() * 10000));
                        System.out.println("No." + NO + "arrived");
                    } catch (InterruptedException e) {
                    } finally {
                        end.countDown();
                    }
                }
            };
            exec.submit(run);
        }

        System.out.println("Game Start");

        begin.countDown();

        end.await();

        System.out.println("Game  Over");

        exec.shutdown();

    }
}

输出结果：

Game Start
No.6arrived
No.8arrived
No.3arrived
No.10arrived
No.7arrived
No.4arrived
No.2arrived
No.5arrived
No.1arrived
No.9arrived
Game  Over