CyclicBarrier

多线程执行的时候确保所有线程到达同一位置后再执行。

ThreadPoolExecutor

线程池，避免频繁新建现场的损耗。

代码示例

package com.fancv.concurrent.ThreadWait;

import java.util.concurrent.*;

/**
 * 要求是一组任务
 *  3 个线程 协作完成一个任务，3个线程都执行完成了 主线程打印任务结果
 *  重试3次
 */
public class CyclicBarrierDemo_2 {
          
   

    ThreadPoolExecutor threadPoolExecutor =new ThreadPoolExecutor(2, 9,
            10L, TimeUnit.MILLISECONDS,
            new LinkedBlockingQueue<Runnable>(3));
     CyclicBarrier cyclicBarrier = new CyclicBarrier(3,()->{
          
   
        System.out.println(Thread.currentThread().getName()+"完成了一组之后 回调执行");
    });

    public static void main(String[] args) throws InterruptedException {
          
   
        CyclicBarrierDemo_2 cyclicBarrierDemo_2=new CyclicBarrierDemo_2();
        cyclicBarrierDemo_2.threeTime();
        //执行shutdown
        if (!cyclicBarrierDemo_2.threadPoolExecutor.isShutdown()) {
          
   
            cyclicBarrierDemo_2.threadPoolExecutor.shutdown();
            System.out.println("start shutdown ...");
            //等待执行结束
            cyclicBarrierDemo_2.threadPoolExecutor.awaitTermination(16, TimeUnit.MINUTES);
        }
    }


    void threeTime(){
          
   
        for (int i=0;i<3;i++){
          
   
            threadPoolExecutor.submit(()->{
          
   
                System.out.println("A");
                try {
          
   
                    Thread.sleep(100);
                    cyclicBarrier.await();
                } catch (InterruptedException e) {
          
   
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
          
   
                    e.printStackTrace();
                }
                System.out.println("A 执行完毕");
            });
            threadPoolExecutor.submit(()->{
          
   
                System.out.println("B");
                try {
          
   
                    Thread.sleep(1000);
                    cyclicBarrier.await();
                } catch (InterruptedException e) {
          
   
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
          
   
                    e.printStackTrace();
                }
                System.out.println("B 执行完毕");
            });
            threadPoolExecutor.submit(()->{
          
   
                System.out.println("C");
                try {
          
   
                    Thread.sleep(1000);
                    cyclicBarrier.await();
                } catch (InterruptedException e) {
          
   
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
          
   
                    e.printStackTrace();
                }
                System.out.println("C 执行完毕");
            });
        }
    }

}

如果线程池参数配置为无界队列那么整个逻辑无法执行，CyclicBarrier 等待三个线程执行完毕，线程池只有两个工作线程，导致资源等待。