/**
CountDownLatch类是一个同步计数器,构造时传入int参数,该参数就是计数器的初始值，每调用一次countDown()方法，计数器减1,计数器大于0 时，await()方法会阻塞程序继续执行
CountDownLatch如其所写，是一个倒计数的锁存器，当计数减至0时触发特定的事件。利用这种特性，可以让主线程等待子线程的结束。下面以一个模拟运动员比赛的例子加以说明。
*/
import java.util.concurrent.CountDownLatch; import java.util.concurrent.Executor; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class CountDownLatchDemo { private static final int PLAYER_AMOUNT = 5; public CountDownLatchDemo() { // TODO Auto-generated constructor stub } /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub //对于每位运动员，CountDownLatch减1后即结束比赛 CountDownLatch begin = new CountDownLatch(1); //对于整个比赛，所有运动员结束后才算结束 CountDownLatch end = new CountDownLatch(PLAYER_AMOUNT); Player[] plays = new Player[PLAYER_AMOUNT]; for(int i=0;i<PLAYER_AMOUNT;i++) plays[i] = new Player(i+1,begin,end); //设置特定的线程池，大小为5 ExecutorService exe = Executors.newFixedThreadPool(PLAYER_AMOUNT); for(Player p:plays) exe.execute(p); //分配线程 System.out.println("Race begins!"); begin.countDown(); try{ end.await(); //等待end状态变为0，即为比赛结束 }catch (InterruptedException e) { // TODO: handle exception e.printStackTrace(); }finally{ System.out.println("Race ends!"); } exe.shutdown(); } }
接下来是Player类
import java.util.concurrent.CountDownLatch; public class Player implements Runnable { private int id; private CountDownLatch begin; private CountDownLatch end; public Player(int i, CountDownLatch begin, CountDownLatch end) { // TODO Auto-generated constructor stub super(); this.id = i; this.begin = begin; this.end = end; } @Override public void run() { // TODO Auto-generated method stub try{ begin.await(); //等待begin的状态为0 Thread.sleep((long)(Math.random()*100)); //随机分配时间，即运动员完成时间 System.out.println("Play"+id+" arrived."); }catch (InterruptedException e) { // TODO: handle exception e.printStackTrace(); }finally{ end.countDown(); //使end状态减1，最终减至0 } } }
来源：https://www.cnblogs.com/yezhenhan/archive/2012/01/07/2315652.html