Java多线程之~~~使用CountDownLatch来同步多个线程实现一个任务

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在多线程开发中，经常会遇到这样的问题，比如，一个线程需要其他的一些辅助线程完成指定的一些任务后才能开

启。类似于一个主线程正在运行，他需要其他分支线程完成一些任务后才能激活他来启动剩下的任务，这里就可以使用

Java自带的CountDownLatch这个类来帮我们实现这样的效果。这个类初始化的时候会指定一个数字，这就是需要等

待的资源的数量，每一个资源到位的时候，就调用他的countDown函数，这样就会将资源减一，知道这个资源数字变成

0的时候，就会叫醒主线程，来完成剩下的功能，下面我们就使用一个例子来说明这样的情况。

package com.bird.concursey.charpet4;import java.util.concurrent.CountDownLatch;public class Videoconference implements Runnable {private CountDownLatch controller;/** * Implement the constructor of the class that initializes the CountDownLatchattribute. The Videoconference class will wait for the arrival of the number ofparticipants received as a parameter. * @param number */public Videoconference(int number) {controller = new CountDownLatch(number);}public void arrive(String name) {System.out.printf("%s has arrived.",name);controller.countDown();System.out.printf("VideoConference: Waiting for %d participants.\n",controller.getCount());}@Overridepublic void run() {System.out.printf("VideoConference: Initialization: %d participants.\n",controller.getCount());try {controller.await();System.out.printf("VideoConference: All the participants have come\n");System.out.printf("VideoConference: Let's start...\n");} catch (InterruptedException e) {e.printStackTrace();}}}

package com.bird.concursey.charpet4;import java.util.concurrent.TimeUnit;public class Participant implements Runnable {private Videoconference videoConference;private String name;public Participant(Videoconference videoConference, String name) {this.videoConference = videoConference;this.name = name;}@Overridepublic void run() {long duration=(long)(Math.random()*10);try {TimeUnit.SECONDS.sleep(duration);} catch (InterruptedException e) {e.printStackTrace();}videoConference.arrive(name);}public static void main(String[] args) {//Create a Videoconference object named conference that waits for 10 participants.Videoconference videoCOnference = new Videoconference(10);Thread threadConference = new Thread(videoCOnference);threadConference.start();for(int i = 0; i < 10; i++) {Participant participant = new Participant(videoCOnference, "participant" + i);Thread t = new Thread(participant);t.start();}}}

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