Java骚操作之CountDownLatch代码详解

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