十一、CountDownLatch-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_45905724/article/details/136822148

本文介绍了如何在Java中使用CountDownLatch实现线程同步，通过创建一个计数器，当所有线程执行完毕后使主线程等待，展示了`usingCountDownLatch`方法的实现及其在控制多线程执行顺序中的作用。

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CountDownLatch 倒数的门栓

CountDownLatch latch = new CountDownLatch(threads.length); 创建一个门栓,在门栓上面记个数
每一个线程结束就countDown
开启线程
latch.await(); 每一个线程结束后线程数减一，当 latch.await()为0的时候门栓就打开

package com.mashibing.juc.c_020;

import java.util.concurrent.CountDownLatch;

public class T06_TestCountDownLatch {
    public static void main(String[] args) {
        usingJoin();
        usingCountDownLatch();
    }

    private static void usingCountDownLatch() {
        Thread[] threads = new Thread[100];
        //创建一个门栓在门栓上面记个数
        CountDownLatch latch = new CountDownLatch(threads.length);

        for(int i=0; i<threads.length; i++) { //每一个线程结束就countDown
            threads[i] = new Thread(()->{
                int result = 0;
                for(int j=0; j<10000; j++) result += j;
                latch.countDown();
            });
        }
        //线程开启
        for (int i = 0; i < threads.length; i++) {
            threads[i].start();
        }

        try { //门栓，拴住不动
            latch.await();  
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("end latch");
    }

    private static void usingJoin() {
        Thread[] threads = new Thread[100];

        for(int i=0; i<threads.length; i++) {
            threads[i] = new Thread(()->{
                int result = 0;
                for(int j=0; j<10000; j++) result += j;
            });
        }

        for (int i = 0; i < threads.length; i++) {
            threads[i].start();
        }

        for (int i = 0; i < threads.length; i++) {
            try {
                threads[i].join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        System.out.println("end join");
    }
}