要使多个线程在做完某个操作，等其他线程做完同样的操作后，同时运行，就要用到CyclicBarrier，代码：

package com.concurrent;

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

import junit.framework.TestCase;

public class TestCyclicBarrier extends TestCase {
	private final int COUNT = 10;

	public void testCyclicBarrier() {
		final CyclicBarrier cb = new CyclicBarrier(COUNT);
		ExecutorService executorService = Executors.newFixedThreadPool(COUNT);
		for (int i = 0; i < COUNT; i++) {
			final int index = i + 1;
			Runnable r = new Runnable() {
				@Override
				public void run() {
					try {
						System.out.println("wait " + index);
						cb.await();
						System.out.println("begin " + index);
					} catch (InterruptedException e) {
						e.printStackTrace();
					} catch (BrokenBarrierException e) {
						e.printStackTrace();
					}
				}
			};
			executorService.submit(r);
		}
		
		executorService.shutdown();
	}
}



输出： 

wait 1
wait 2
wait 4
wait 3
wait 5
wait 6
wait 7
wait 8
wait 9
wait 10
begin 10
begin 2
begin 4
begin 1
begin 3
begin 7
begin 8
begin 9
begin 6
begin 5



看到都是wait之后才输出begin，没有哪个begin是夹在两个wait之间的。