java多线程----CountDownLatch-优快云博客

本文介绍了一个使用CountDownLatch来实现线程间同步的例子。主线程通过CountDownLatch的await方法等待五个子线程执行完毕。每个子线程在完成任务后调用countDown方法，递减CountDownLatch的计数器。当计数器归零时，主线程继续执行。

package com.test;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.CyclicBarrier;

public class CountDownLatchTest1 {

    private static int LATCH_SIZE = 5;
    private static CountDownLatch doneSignal;
    public static void main(String[] args) {

        try {
            doneSignal = new CountDownLatch(LATCH_SIZE);

            // 新建5个任务
            for(int i=0; i<LATCH_SIZE; i++)
                new InnerThread().start();

            System.out.println("main await begin.");
            // "主线程"等待线程池中5个任务的完成
            doneSignal.await();

            System.out.println("main await finished.");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    static class InnerThread extends Thread{
        public void run() {
            try {
                Thread.sleep(1000);
                System.out.println(Thread.currentThread().getName() + " sleep 1000ms.");
                // 将CountDownLatch的数值减1
                doneSignal.countDown();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

结果说明：主线程通过doneSignal.await()等待其它线程将doneSignal递减至0。其它的5个InnerThread线程，每一个都通过doneSignal.countDown()将doneSignal的值减1；当doneSignal为0时，main被唤醒后继续执行。