CyclicBarrier

 /**
  * CyclicBarrier 线程计数器
  *
  */
 1 import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierTest {
    private static final int THREAD_COUNT = 10;
    
    public static CyclicBarrier barrier = new CyclicBarrier(THREAD_COUNT);
    
    public static void main(String[] args) {
        for(int i = 0; i<THREAD_COUNT; i++){
            new Thread(new WorkThread(barrier)).start();
        }
    }
        
}

class WorkThread implements Runnable{
    private CyclicBarrier barrier;
    
    public WorkThread(CyclicBarrier barrier){
        this.barrier = barrier;
    }
    
    @Override
    public void run() {
        try {
            System.out.println(Thread.currentThread().getName() + "working before await()");
            barrier.await();//线程在此等待，直到所有线程到达。。。才开始往下执行
            System.out.println(Thread.currentThread().getName() + "working after await()");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (BrokenBarrierException e) {
            e.printStackTrace();
        }
    }
}

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