java并发初探CyclicBarrier

CyclicBarrier的作用

CyclicBarrier，“循环屏障”的作用就是一系列的线程等待直至达到屏障的“瓶颈点”。
具体的使用就是就是一些列的线程调用CyclicBarrier得await()方法进入等待，直至达到
CyclicBarrier设置的barrier size，其他的线程会继续运行。

    /*** 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* <em>cyclic</em> because it can be re-used after the waiting threads* are released.*/

CyclicBarrier源码

成员变量

    /** The lock for guarding barrier entry */private final ReentrantLock lock = new ReentrantLock();/** Condition to wait on until tripped */private final Condition trip = lock.newCondition();/** The number of parties */private final int parties;/* The command to run when tripped */private final Runnable barrierCommand;/** The current generation */private Generation generation = new Generation();

构造器

    public CyclicBarrier(int parties, Runnable barrierAction) {if (parties <= 0) throw new IllegalArgumentException();this.parties = parties;this.count = parties;this.barrierCommand = barrierAction;}public CyclicBarrier(int parties) {this(parties, null);}

例子

package com.java.javabase.thread.base.concurrent.lock;import lombok.extern.slf4j.Slf4j;import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;/*** @author*/
@Slf4j
public class CyclicBarrierTest {public static int size = 5;private static CyclicBarrier cyclicBarrier = new CyclicBarrier(size, () -> log.info("thread :{} run after barrier broken", Thread.currentThread().getName()));public static void main(String[] args) {for (int i = 0; i < size; i++) {new Thread() {@Overridepublic void run() {try {log.info("thread : {}, begin", Thread.currentThread().getName());cyclicBarrier.await();} catch (InterruptedException e) {e.printStackTrace();} catch (BrokenBarrierException e) {e.printStackTrace();}log.info("thread : {}, end", Thread.currentThread().getName());}}.start();}}
}

例子结果

2019-08-12 11:04:07,511   [Thread-0] INFO  CyclicBarrierTest  - thread : Thread-0, begin
2019-08-12 11:04:07,511   [Thread-2] INFO  CyclicBarrierTest  - thread : Thread-2, begin
2019-08-12 11:04:07,511   [Thread-4] INFO  CyclicBarrierTest  - thread : Thread-4, begin
2019-08-12 11:04:07,511   [Thread-1] INFO  CyclicBarrierTest  - thread : Thread-1, begin
2019-08-12 11:04:07,511   [Thread-3] INFO  CyclicBarrierTest  - thread : Thread-3, begin
2019-08-12 11:04:07,511   [Thread-3] INFO  CyclicBarrierTest  - thread :Thread-3 run after barrier broken
2019-08-12 11:04:07,511   [Thread-3] INFO  CyclicBarrierTest  - thread : Thread-3, end
2019-08-12 11:04:07,511   [Thread-0] INFO  CyclicBarrierTest  - thread : Thread-0, end
2019-08-12 11:04:07,511   [Thread-2] INFO  CyclicBarrierTest  - thread : Thread-2, end
2019-08-12 11:04:07,511   [Thread-4] INFO  CyclicBarrierTest  - thread : Thread-4, end
2019-08-12 11:04:07,511   [Thread-1] INFO  CyclicBarrierTest  - thread : Thread-1, end