CyclicBarrier

 /**
  * CyclicBarrier 线程计数器
  *
  */
 1 import java.util.concurrent.BrokenBarrierException;
 2 import java.util.concurrent.CyclicBarrier;
 3 
 4 public class CyclicBarrierTest {
 5     private static final int THREAD_COUNT = 10;
 6     
 7     public static CyclicBarrier barrier = new CyclicBarrier(THREAD_COUNT);
 8     
 9     public static void main(String[] args) {
10         for(int i = 0; i<THREAD_COUNT; i++){
11             new Thread(new WorkThread(barrier)).start();
12         }
13     }
14         
15 }
16 
17 class WorkThread implements Runnable{
18     private CyclicBarrier barrier;
19     
20     public WorkThread(CyclicBarrier barrier){
21         this.barrier = barrier;
22     }
23     
24     @Override
25     public void run() {
26         try {
27             System.out.println(Thread.currentThread().getName() + "working before await()");
28             barrier.await();//线程在此等待，直到所有线程到达。。。才开始往下执行
29             System.out.println(Thread.currentThread().getName() + "working after await()");
30         } catch (InterruptedException e) {
31             e.printStackTrace();
32         } catch (BrokenBarrierException e) {
33             e.printStackTrace();
34         }
35     }
36 }

结果

Thread-0working before await()
Thread-1working before await()
Thread-3working before await()
Thread-2working before await()
Thread-5working before await()
Thread-4working before await()
Thread-7working before await()
Thread-9working before await()
Thread-6working before await()
Thread-8working before await()

Thread-0working after await()
Thread-8working after await()
Thread-1working after await()
Thread-3working after await()
Thread-2working after await()
Thread-5working after await()
Thread-4working after await()
Thread-9working after await()
Thread-6working after await()
Thread-7working after await()

从上面的结果，可以知道：

 CyclicBarrier barrier = new CyclicBarrier(THREAD_COUNT); 当调用barrier.await()方法时，当所有线程到达时，才会开始执行后面的代码。这个类很有用，平时自己做一些测试例子是比较常用的