Java CountDownLatch 实战

淩亂°似流年 2021-07-25 01:01 350阅读 0赞

# 一 点睛 #

## 1 CountDownLatch 定义 ##

> Thread\[\] threads = new Thread\[100\];
> 
> CountDownLatch latch = new CountDownLatch(threads.length);

## 2 CountDownLatch 让线程 wait ##

> try \{
> 
>     latch.await();
> 
> \} catch (InterruptedException e) \{
> 
>     e.printStackTrace();
> 
> \}

## 3 CountDownLatch  让线程等待结束 ##

> latch.countDown(); // 当减到0，也就是各线程结束，程序继续往下走

# 二 代码 #

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

## 三 测试 ##

> end join
> 
> end latch

## 四 说明 ##

CountDownLatch 起到了 join 的作用。