CyclicBarrier 线程的一个辅助类，就称它为 线程等待器

CyclicBarrier是一个线程辅助类，在初始化时，指定所要等待的线程等待数，调用await方法会使线程处于等待状态，直到等待的线程数达到指定的数。

下面是小实例：

import java.util.Random;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
 * 线程等待器
 * @author YangBaoBao
 *
 */
public class CyclicBarrierDemo {

 public static void main(String[] args) {
  ExecutorService service=Executors.newCachedThreadPool();
  final CyclicBarrier barrier = new CyclicBarrier(5);
  for (int i = 0; i < 5; i++) {
   Runnable runnable = new Runnable() {

    public void run() {
     try {
      Thread.sleep(new Random().nextInt(2000));
      System.out.println("1正在等待的线程有："+barrier.getNumberWaiting()+" 个");
      barrier.await();
      System.out.println("1人数到全："+barrier.getParties()+"  go");
      
      Thread.sleep(new Random().nextInt(2000));
      System.out.println("2正在等待的线程有："+barrier.getNumberWaiting()+" 个");
      barrier.await();
      System.out.println("2人数到全："+barrier.getParties()+"  go");
      
     } catch (Exception e) {
      e.printStackTrace();
     }
    }
   };
   service.execute(runnable);
  }
 }
}