CountDownLatch的使用(倒计时计数器)

countDown()将计数器减一
await()等待计数器值为0,当到达0时所有等待者开始执行import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CountdownLatchTest {

    public static void main(String[] args) {
        ExecutorService service = Executors.newCachedThreadPool(); 
        final CountDownLatch cdOrder = new CountDownLatch(1);
        final CountDownLatch cdAnswer = new CountDownLatch(3);
        for(int i=0;i<3;i++){
            Runnable runnable = new Runnable(){
                    public void run(){
                    try {
                        System.out.println("线程" + Thread.currentThread().getName() + 
                                "正准备接受命令");                        
                        cdOrder.await(); 
                        System.out.println("线程" + Thread.currentThread().getName() + 
                        "已接受命令");                                
                        Thread.sleep((long)(Math.random()*10000));    
                        System.out.println("线程" + Thread.currentThread().getName() + 
                                "回应命令处理结果");                        
                        cdAnswer.countDown();          
                    } catch (Exception e) {
                        e.printStackTrace();
                    }                
                }
            };
            service.execute(runnable);
        }        
        try {
            Thread.sleep((long)(Math.random()*10000));
        
            System.out.println("线程" + Thread.currentThread().getName() + 
                    "即将发布命令");                        
            cdOrder.countDown(); 
            System.out.println("线程" + Thread.currentThread().getName() + 
            "已发送命令，正在等待结果");    
            cdAnswer.await(); 
            System.out.println("线程" + Thread.currentThread().getName() + 
            "已收到所有响应结果");    
        } catch (Exception e) {
            e.printStackTrace();
        }                
        service.shutdown(); 

    }
}