使用java并发工具栅栏(CyclicBarrier)实现多线程等待,同一时刻执行共同任务
CyclicBarrier,名字就是循环栅栏,栅栏显而易见就是拦住一堆"事情",这里"事情"就是线程,在未达到栅栏指定的线程数时,所有线程都要等待,达到指定数目,共同执行下面的任务。api文档解释:
A synchronization aid that allows a set of threads to all wait for each other to reach a common barrier point. CyclicBarriers are useful in programs involving a fixed sized party of threads that must occasionally wait for each other. The barrier is called cyclic because it can be re-used after the waiting threads are released.
下面设定一个场景,在运动场上,所有运动员自由走到起跑线,在发令枪发令之前,可以自由热身,但是一旦所有队员已经走到起跑线并准备好,裁判发号施令。程序如下:
package com.smikevon.concurrent.tools; import java.util.Random; import java.util.concurrent.BrokenBarrierException; import java.util.concurrent.CyclicBarrier; /** * @description: 要求:十个运动员要进行百米赛跑,在赛前运动员各自进行自己的热身运动,然后统一起跑,裁判才开始记时。 * @date : 2014年9月17日 下午4:22:15 */ public class TestCyclicBarrier { public static void main(String[] args) throws InterruptedException { String[] children = {"小明(1号)","小强(2号)","小海(3号)","小龙(4号)","小武(5号)","小勇(6号)","小鹏(7号)","小飞(8号)","小峰(9号)","小涛(10号)"}; final Random random = new Random(System.currentTimeMillis()); final CyclicBarrier barrier = new CyclicBarrier(10,new Runnable() { public void run() { Thread.currentThread().setName("裁判"); doing("各就各位,预备,跑"); } }); //让10个运动员动起来 for(String child : children){ new Thread(new Runnable() { public void run() { try { doing("我要开始做我的热身运动!"); int time = random.nextInt(20000); Thread.sleep(time); doing("我已经做完了热身运动!共耗时"+Long.parseLong(time+"")/1000+"秒!"); //等待其他线程执行 barrier.await(); doing("我已经准备好,当前时间是:"+System.currentTimeMillis()); } catch (InterruptedException e) { e.printStackTrace(); } catch (BrokenBarrierException e) { e.printStackTrace(); } } },child).start(); } } /** * @Description:打印出线程的名字 * @param msg * @returType:void */ public static void doing(String msg){ System.out.println(Thread.currentThread().getName()+":"+msg); } }
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