CyclicBarrier 使用说明

字面意思回环栅栏，通过它可以实现让一组线程等待至某个状态之后再全部同时执行。叫做回环是因为当所有等待线程都被释放以后，CyclicBarrier可以被重用。

主要方法：

public int await() throws InterruptedException, BrokenBarrierException

用来挂起当前线程，直至所有线程都到达barrier状态再同时执行后续任务。

例子：

跟团旅游，没到一个景点导游给介绍完后，让大家自由活动，然后约定好（某个时间）在下一个景点集合。

 1 import java.util.concurrent.CyclicBarrier;
 2 import java.util.concurrent.ExecutorService;
 3 import java.util.concurrent.Executors;
 4  
 5 public class CyclicBarrierTest {
 6  
 7         public static void main(String[] args) {
 8               ExecutorService service = Executors. newCachedThreadPool();
 9                final CyclicBarrier cb = new CyclicBarrier(3);
10                for(int i = 0; i < 3; i++){
11                      Runnable runnable = new Runnable(){
12                             public void run(){
13                                    try {
14                                          Thread. sleep((long)(Math. random()*10000));     
15                                          System. out.println("线程" + Thread.currentThread().getName() +
16                                                         "即将到达集合地点1，当前已有" + (cb.getNumberWaiting()+1) + "个已经到达，" + (cb.getNumberWaiting()==2?"都到齐了，继续走啊":"正在等候" ));                                        
17                                          cb.await();
18                                          
19                                          Thread. sleep((long)(Math. random()*10000));     
20                                          System. out.println("线程" + Thread.currentThread().getName() +
21                                                         "即将到达集合地点2，当前已有" + (cb.getNumberWaiting()+1) + "个已经到达，" + (cb.getNumberWaiting()==2?"都到齐了，继续走啊":"正在等候" ));
22                                          cb.await();   
23                                          Thread. sleep((long)(Math. random()*10000));     
24                                          System. out.println("线程" + Thread.currentThread().getName() +
25                                                         "即将到达集合地点3，当前已有" + (cb.getNumberWaiting() + 1) + "个已经到达，" + (cb.getNumberWaiting()==2?"都到齐了，继续走啊":"正在等候" ));                                      
26                                          cb.await();                                     
27                                   } catch (Exception e) {
28                                          e.printStackTrace();
29                                   }                          
30                            }
31                      };
32                      service.execute(runnable);
33               }
34               service.shutdown();
35        }
36 }