java并发初探CyclicBarrier

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() {
                @Override
                public 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