Java CyclicBarrier

矫情吗；* 2023-10-05 18:55 14阅读 0赞

在本文中，我们将介绍Java中的CyclicBarrier。在Java 5中，CyclicBarrier与其他并发实用程序（如[CountDownLatch][]，[ConcurrentHashMap][]和[BlockingQueue）][BlockingQueue]一起引入。

CyclicBarrier是同步的辅助工具，它允许线程集在公共的屏障点处彼此等待。之所以称为循环的，是因为一旦释放等待的线程，它便可以重用。

例如：  
假设您有3个线程，您希望所有线程（称为当事人）达到一个共同点，然后只有它们才可以继续前进。在这种情况下，您可以将CyclicBarrier与3个当事人一起使用，一旦3个线程达到一个共同点可以调用一个将实现可运行接口的事件，并释放三个线程。

### **CountDownLatch和CyclicBarrier之间的区别** ###

CyclicBarrier和CoundDownLatch之间的主要区别是CyclicBarrier可以重用。一次使用后不能使用CountDownLatch。您可以阅读[CountDownLatch和CyclicBarrier之间的][CountDownLatch_CyclicBarrier]更多[区别。][CountDownLatch_CyclicBarrier]

### **Java CyclicBarrier示例：** ###

**步骤1：**在包.src.org.arpit.java2blog中创建一个名为“ RunnableTask.java”的文件

<table style="margin-left:-29px;"> 
 <tbody> 
 <tr> 
 <td style="vertical-align:top;"> 
 <div style="margin-left:0px;"> 
 <div style="margin-left:0px;"> 
 1 
 </div> 
 <div style="margin-left:0px;"> 
 2 
 </div> 
 <div style="margin-left:0px;"> 
 3 
 </div> 
 <div style="margin-left:0px;"> 
 4 
 </div> 
 <div style="margin-left:0px;"> 
 5 
 </div> 
 <div style="margin-left:0px;"> 
 6 
 </div> 
 <div style="margin-left:0px;"> 
 7 
 </div> 
 <div style="margin-left:0px;"> 
 8 
 </div> 
 <div style="margin-left:0px;"> 
 9 
 </div> 
 <div style="margin-left:0px;"> 
 10 
 </div> 
 <div style="margin-left:0px;"> 
 11 
 </div> 
 <div style="margin-left:0px;"> 
 12 
 </div> 
 <div style="margin-left:0px;"> 
 13 
 </div> 
 <div style="margin-left:0px;"> 
 14 
 </div> 
 <div style="margin-left:0px;"> 
 15 
 </div> 
 <div style="margin-left:0px;"> 
 16 
 </div> 
 <div style="margin-left:0px;"> 
 17 
 </div> 
 <div style="margin-left:0px;"> 
 18 
 </div> 
 <div style="margin-left:0px;"> 
 19 
 </div> 
 <div style="margin-left:0px;"> 
 20 
 </div> 
 <div style="margin-left:0px;"> 
 21 
 </div> 
 <div style="margin-left:0px;"> 
 22 
 </div> 
 <div style="margin-left:0px;"> 
 23 
 </div> 
 <div style="margin-left:0px;"> 
 24 
 </div> 
 <div style="margin-left:0px;"> 
 25 
 </div> 
 <div style="margin-left:0px;"> 
 26 
 </div> 
 <div style="margin-left:0px;"> 
 27 
 </div> 
 <div style="margin-left:0px;"> 
 28 
 </div> 
 <div style="margin-left:0px;"> 
 29 
 </div> 
 <div style="margin-left:0px;"> 
 30 
 </div> 
 <div style="margin-left:0px;"> 
 31 
 </div> 
 <div style="margin-left:0px;"> 
 32 
 </div> 
 <div style="margin-left:0px;"> 
 33 
 </div> 
 <div style="margin-left:0px;"> 
 34 
 </div> 
 <div style="margin-left:0px;"> 
 35 
 </div> 
 <div style="margin-left:0px;"> 
 36 
 </div> 
 <div style="margin-left:0px;"> 
 37 
 </div> 
 <div style="margin-left:0px;"> 
 38 
 </div> 
 <div style="margin-left:0px;"> 
 39 
 </div> 
 <div style="margin-left:0px;"> 
 40 
 </div> 
 <div style="margin-left:0px;"> 
 41 
 </div> 
 <div style="margin-left:0px;"> 
 42 
 </div> 
 </div> </td> 
 <td style="vertical-align:top;"> 
 <div style="margin-left:0px;"> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 package org.arpit.java2blog; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 import java.util.concurrent.BrokenBarrierException; 
 </div> 
 <div style="margin-left:0px;"> 
 import java.util.concurrent.CyclicBarrier; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 public class RunnableTask implements Runnable{ 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;CyclicBarrier cyclicBarrier; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;long sleepTime; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;RunnableTask(CyclicBarrier cyclicBarrier,long sleepTime){ 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;this.cyclicBarrier=cyclicBarrier; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;this.sleepTime=sleepTime; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;} 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;@Override 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;public void run() { 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;try { 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Thread.sleep(sleepTime); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(Thread.currentThread().getName() + 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" is waiting for "+(cyclicBarrier.getParties()-cyclicBarrier.getNumberWaiting()-1)+ 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" other threads to reach common barrier point"); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/* 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; * when&nbsp;&nbsp;3 parties will call await() method (i.e. common barrier point) 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; * CyclicBarrrierEvent will be triggered and all waiting threads will be released. 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */ 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;cyclicBarrier.await(); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} catch (InterruptedException e) { 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;e.printStackTrace(); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} catch (BrokenBarrierException e) { 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;e.printStackTrace(); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println("As "+cyclicBarrier.getParties()+ " threads have reached common barrier point " 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;+ Thread.currentThread().getName() + 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" has been released"); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;} 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 } 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 </div> </td> 
 </tr> 
 </tbody> 
</table>

这是一个Runnable任务，将由每个线程执行。  
**步骤2：**在包.src.org.arpit.java2blog中创建一个名为“ CyclicBarrierFinishEvent.java”的文件

当3个参与方（由CyclicBarrier对象初始化）到达一个公共障碍点时，将调用CyclicBarrierFinishEvent。  
**步骤3：**在包.src.org.arpit.java2blog中创建一个名为“ CyclicBarrierMain.java”的文件

<table style="margin-left:-29px;"> 
 <tbody> 
 <tr> 
 <td style="vertical-align:top;"> 
 <div style="margin-left:0px;"> 
 <div style="margin-left:0px;"> 
 1 
 </div> 
 <div style="margin-left:0px;"> 
 2 
 </div> 
 <div style="margin-left:0px;"> 
 3 
 </div> 
 <div style="margin-left:0px;"> 
 4 
 </div> 
 <div style="margin-left:0px;"> 
 5 
 </div> 
 <div style="margin-left:0px;"> 
 6 
 </div> 
 <div style="margin-left:0px;"> 
 7 
 </div> 
 <div style="margin-left:0px;"> 
 8 
 </div> 
 <div style="margin-left:0px;"> 
 9 
 </div> 
 <div style="margin-left:0px;"> 
 10 
 </div> 
 <div style="margin-left:0px;"> 
 11 
 </div> 
 <div style="margin-left:0px;"> 
 12 
 </div> 
 <div style="margin-left:0px;"> 
 13 
 </div> 
 <div style="margin-left:0px;"> 
 14 
 </div> 
 <div style="margin-left:0px;"> 
 15 
 </div> 
 <div style="margin-left:0px;"> 
 16 
 </div> 
 <div style="margin-left:0px;"> 
 17 
 </div> 
 <div style="margin-left:0px;"> 
 18 
 </div> 
 <div style="margin-left:0px;"> 
 19 
 </div> 
 <div style="margin-left:0px;"> 
 20 
 </div> 
 <div style="margin-left:0px;"> 
 21 
 </div> 
 <div style="margin-left:0px;"> 
 22 
 </div> 
 <div style="margin-left:0px;"> 
 23 
 </div> 
 <div style="margin-left:0px;"> 
 24 
 </div> 
 <div style="margin-left:0px;"> 
 25 
 </div> 
 <div style="margin-left:0px;"> 
 26 
 </div> 
 <div style="margin-left:0px;"> 
 27 
 </div> 
 <div style="margin-left:0px;"> 
 28 
 </div> 
 <div style="margin-left:0px;"> 
 29 
 </div> 
 <div style="margin-left:0px;"> 
 30 
 </div> 
 <div style="margin-left:0px;"> 
 31 
 </div> 
 <div style="margin-left:0px;"> 
 32 
 </div> 
 <div style="margin-left:0px;"> 
 33 
 </div> 
 <div style="margin-left:0px;"> 
 34 
 </div> 
 <div style="margin-left:0px;"> 
 35 
 </div> 
 <div style="margin-left:0px;"> 
 36 
 </div> 
 <div style="margin-left:0px;"> 
 37 
 </div> 
 <div style="margin-left:0px;"> 
 38 
 </div> 
 <div style="margin-left:0px;"> 
 39 
 </div> 
 <div style="margin-left:0px;"> 
 40 
 </div> 
 </div> </td> 
 <td style="vertical-align:top;"> 
 <div style="margin-left:0px;"> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 package org.arpit.java2blog; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 import java.util.concurrent.CyclicBarrier; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 /** @author Arpit Mandliya*/ 
 </div> 
 <div style="margin-left:0px;"> 
 public class CyclicBarrierMain { 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;public static void main(String[] args) { 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/* 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; * Create CountDownLatch with 3 parties, when all 3 parties 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; * will reach common barrier point CyclicBarrrierFinishEvent will be 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; * triggered 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */ 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;CyclicBarrier cyclicBarrier=new CyclicBarrier(3 ,new CyclicBarrierFinishEvent()); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;RunnableTask runnableTask1=new RunnableTask(cyclicBarrier,1000); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;RunnableTask runnableTask2=new RunnableTask(cyclicBarrier,2000); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;RunnableTask runnableTask3=new RunnableTask(cyclicBarrier,3000); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//Create and start 3 threads 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new Thread(runnableTask1,"Thread-1").start(); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new Thread(runnableTask2,"Thread-2").start(); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new Thread(runnableTask3,"Thread-3").start(); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/* 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; * We are reusing cyclic barrier using below threads 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; * */ 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;RunnableTask runnableTask4=new RunnableTask(cyclicBarrier,4000); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;RunnableTask runnableTask5=new RunnableTask(cyclicBarrier,5000); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;RunnableTask runnableTask6=new RunnableTask(cyclicBarrier,6000); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Create and start 3 more threads 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new Thread(runnableTask4,"Thread-4").start(); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new Thread(runnableTask5,"Thread-5").start(); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new Thread(runnableTask6,"Thread-6").start(); 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp;&nbsp;&nbsp;&nbsp;} 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 <div style="margin-left:0px;"> 
 } 
 </div> 
 <div style="margin-left:0px;"> 
 &nbsp; 
 </div> 
 </div> </td> 
 </tr> 
 </tbody> 
</table>

让我们运行程序，然后我们将理解输出：

线程1等待其他2个线程到达公共障碍点  
线程2等待其他1个线程到达公共障碍点  
线程3等待其他0个线程到达公共障碍点  
由于3个线程到达了公共障碍点，已触发CyclicBarrrierFinishEvent。  
如果有以下任何情况，您可以更新共享变量：  
3个线程已到达公共障碍点Thread-3已释放  
3个线程已到达公共障碍点Thread-1已释放  
3个线程已到达公共障碍点Thread- 2已发布  
线程4正在等待其他2个线程到达公共障碍点  
线程5正在等待其他2个线程到达公共障碍点  
线程6正在等待其他0个线程到达公共障碍点  
由于3个线程已到达公共障碍点，CyclicBarrrierFinishEvent已触发  
您可以更新共享变量（如果有）  
当3个线程已到达公共障碍点时线程6已被释放  
3线程已达到公共障碍点Thread-4已被释放  
由于3个线程已达到公共障碍点Thread-5已被释放

下图将使您更好地理解输出。

![循环屏障输出][c868ba2afb9f8c4824bd9f23b1789640.png]

这就是关于Java CyclicBarrier示例的全部内容。

[CountDownLatch]: https://www.java2blog.com/2015/08/countdownlatch-in-java.html
[ConcurrentHashMap]: https://www.java2blog.com/2014/11/concurrenthashmap-in-java.html
[BlockingQueue]: https://www.java2blog.com/2015/12/blockingqueue-in-java.html
[CountDownLatch_CyclicBarrier]: https://www.java2blog.com/2016/07/difference-between-countdownlatch-and-cyclicbarrier-in-java.html
[c868ba2afb9f8c4824bd9f23b1789640.png]: https://img-blog.csdnimg.cn/img_convert/c868ba2afb9f8c4824bd9f23b1789640.png