Java中CountDownLatch怎么用

簡述

用來干嘛的？當(dāng)你在方法中調(diào)用了多個線程，對數(shù)據(jù)庫進(jìn)行了一些不為人知的操作后，還有一個操作需要留到前者都執(zhí)行完的重頭戲，就需要用到 CountDownLatch 了

實踐代碼

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("此處對數(shù)據(jù)庫進(jìn)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()
                        + "對數(shù)據(jù)庫進(jìn)行插入，持續(xù)時間：" + this.times / 1000 + "秒");
                Thread.sleep(times);
                countDownLatch.countDown();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

圖解

 

使用await()提前結(jié)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("~~~賈總PPT巡演~~~~");
        System.out.println("~~~~融資完成，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("負(fù)責(zé)人：" + Thread.currentThread().getName()
                        + "開始工作，持續(xù)時間：" + this.times / 1000 + "秒");
                countDownLatch.countDown();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

假設(shè)公司一、公司二、公司三各需要2s、3s、5s來完成工作，賈總等不了，只能等2s，那么就設(shè)置await的超時時間

latch.await(2, TimeUnit.SECONDS);

執(zhí)行結(jié)果

負(fù)責(zé)人：公司一開始工作，持續(xù)時間：2秒
~~~賈總PPT巡演~~~~
~~~~融資完成，撒花~~~~
負(fù)責(zé)人：公司二開始工作，持續(xù)時間：3秒
負(fù)責(zé)人：公司三開始工作，持續(xù)時間：5秒

方法描述