简述

用来干嘛的？当你在方法中调用了多个线程，对数据库进行了一些不为人知的操作后，还有一个操作需要留到前者都执行完的重头戏，就需要用到 CountDownLatch 了

实践代码

package com.github.gleans;import java.util.concurrent.CountDownLatch;public class TestCountDownLatch { public static void main(String[] args) throws InterruptedException { CountDownLatch latch = new CountDownLatch(3); new KeyPass(1000L, "thin jack", latch).start(); new KeyPass(2000L, "noral jack", latch).start(); new KeyPass(3000L, "fat jack", latch).start(); latch.await(); System.out.println("此处对数据库进行最后的插入操作~"); } static class KeyPass extends Thread { private long times; private CountDownLatch countDownLatch; public KeyPass(long times, String name, CountDownLatch countDownLatch) { super(name); this.times = times; this.countDownLatch = countDownLatch; } @Override public void run() { try { System.out.println("操作人：" + Thread.currentThread().getName() + "对数据库进行插入，持续时间：" + this.times / 1000 + "秒"); Thread.sleep(times); countDownLatch.countDown(); } catch (InterruptedException e) { e.printStackTrace(); } } }}

图解

使用await()提前结束操作

package com.github.gleans;import java.util.concurrent.CountDownLatch;import java.util.concurrent.TimeUnit;public class TestCountDownLatch { public static void main(String[] args) throws InterruptedException { CountDownLatch latch = new CountDownLatch(3); new KeyPass(2000L, "公司一", latch).start(); new KeyPass(3000L, "公司二", latch).start(); new KeyPass(5000L, "公司三", latch).start(); latch.await(2, TimeUnit.SECONDS); System.out.println("~~~贾总PPT巡演~~~~"); System.out.println("~~~~融资完成，撒花~~~~"); } static class KeyPass extends Thread { private long times; private CountDownLatch countDownLatch; public KeyPass(long times, String name, CountDownLatch countDownLatch) { super(name); this.times = times; this.countDownLatch = countDownLatch; } @Override public void run() { try { Thread.sleep(times); System.out.println("负责人：" + Thread.currentThread().getName() + "开始工作，持续时间：" + this.times / 1000 + "秒"); countDownLatch.countDown(); } catch (InterruptedException e) { e.printStackTrace(); } } }}

假设公司一、公司二、公司三各需要2s、3s、5s来完成工作，贾总等不了，只能等2s，那么就设置await的超时时间

latch.await(2, TimeUnit.SECONDS);

执行结果

负责人：公司一开始工作，持续时间：2秒
~~~贾总PPT巡演~~~~
~~~~融资完成，撒花~~~~
负责人：公司二开始工作，持续时间：3秒
负责人：公司三开始工作，持续时间：5秒

方法描述

总结

这个操作可以说是简单好用，目前还未遇见副作用，若是有大佬，可以告知弟弟一下，提前表示感谢~

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