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*活动，然后约定好（某个时间）在下一个景点集合。

 import java.util.concurrent.CyclicBarrier;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;

 public class CyclicBarrierTest {

         public static void main(String[] args) {
               ExecutorService service = Executors. newCachedThreadPool();
                final CyclicBarrier cb = new CyclicBarrier(3);
                for(int i = 0; i < 3; i++){
                      Runnable runnable = new Runnable(){
                             public void run(){
                                    try {
                                          Thread. sleep((long)(Math. random()*10000));
                                          System. out.println("线程" + Thread.currentThread().getName() +
                                                         "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" ));
                                          cb.await();

                                          Thread. sleep((long)(Math. random()*10000));
                                          System. out.println("线程" + Thread.currentThread().getName() +
                                                         "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" ));
                                          cb.await();
                                          Thread. sleep((long)(Math. random()*10000));
                                          System. out.println("线程" + Thread.currentThread().getName() +
                                                         "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" ));
                                          cb.await();
                                   } catch (Exception e) {
                                          e.printStackTrace();
                                   }
                            }
                      };
                      service.execute(runnable);
               }
               service.shutdown();
        }
 }