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concurrent之初识CountDownLatch(计数器),多线程并行处理

程序员文章站 2022-05-04 21:40:12
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CountDownLatch:

是一个同步工具类,它允许一个或多个线程一直等待,直到其他线程执行完后再执行

详细介绍参考:

https://blog.csdn.net/qq812908087/article/details/81112188

用法:

声明计数器以及计数

CountDownLatch countDownLatch = new CountDownLatch(1);

计数器不为0,则线程处于等待唤醒状态。为0,则线程开始执行任务

countDownLatch.await();

计数器减1

countDownLatch.countDown();

 

场景1:

一个典型应用场景就是启动一个服务时,主线程需要等待多个组件加载完毕,之后再继续执行。

场景2:

类似于赛跑,将多个线程放到起点,等待发令枪响,然后同时开跑。做法是初始化一个共享的CountDownLatch(1),将其计数器初始化为1,多个线程在开始执行任务前首先 coundownlatch.await(),当主线程调用 countDown() 时,计数器变为0,多个线程同时被唤醒。
 

测试代码:

package com.demo;

import java.util.concurrent.CountDownLatch;

/**
 * @Description
 * @Author by mocar小师兄
 * @Date 2020/3/12 14:17
 **/
public class CountDownLatch_one {
    private static final int testCount = Runtime.getRuntime().availableProcessors();

    private static class TaskTest implements Runnable{
        private CountDownLatch countDownLatch;
        private CountDownLatch await;

        public TaskTest(CountDownLatch countDownLatch, CountDownLatch await) {
            this.countDownLatch = countDownLatch;
            this.await = await;
        }

        @Override
        public void run() {
            try {
                countDownLatch.await();
                System.out.println(Thread.currentThread().getName() + "\t 子线程启动组件");
                await.countDown();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                System.out.println(Thread.currentThread().getName() + "\t 子线程启动组件完成");
            }
        }
    }

    /**
     * 功能描述: 线程并行处理
     * 〈〉
     * @Param: [args]
     * @Return: void
     * @Author: by
     * @Date: 2020/3/12 14:31
     */
    public static void main(String[] args) {
        CountDownLatch countDownLatch = new CountDownLatch(1);
        CountDownLatch await = new CountDownLatch(testCount);
        System.out.println("主线程开始启动服务");
        for (int i = 0; i <testCount ; i++) {
            new Thread(new TaskTest(countDownLatch,await),"线程" + i).start();
        }
        try {
            System.out.println("子线程开始启动组件");
            countDownLatch.countDown();
            await.await();
            System.out.println("子线程完成启动组件");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("主线程完成启动服务");

    }
}

 

结果显示:

main主线程先执行,然后是开启任务处于等待状态。当countDownLatch这个计数器为0时,开始唤醒子线程并行执行任务,此时主线程处于等待唤醒状态。当多个子线程任务执行完,再执行主线程任务。

 

concurrent之初识CountDownLatch(计数器),多线程并行处理

 

 

相关标签: concurrent