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

               

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()); }  @Override public 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; } @Override public 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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