12.线程通信CyclicBarrier

CountDownLatch

监听某个线程的初始化，等待初始化执行完毕后，通知主线程工作。延迟、阻塞的是主线程，在单个线程中。

CyclicBarrier

针对多个线程、线程池，多个线程初始化准备之后，去操作同一件事件(必须一定要所有准备才可执行，通知各的主线程去执行正常工作)。

package demo2;

import java.util.Random;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * Created by liudan on 2017/7/30.
 */
public class DemoCyclicBarrier {


    /**
     * 假设一个场景：3个运动员，当跑步运动员准备好了，才一起出发
     */


    static class Runner implements Runnable {

        private CyclicBarrier CYCLIC_BARRIER;
        private String name;

        public Runner(CyclicBarrier CYCLIC_BARRIER, String name) {
            this.CYCLIC_BARRIER = CYCLIC_BARRIER;
            this.name = name;
        }

        @Override
        public void run() {
            try {
                Thread.sleep(1000 * (new Random().nextInt(5)));
                System.err.println(name + "\t准备好了");
                CYCLIC_BARRIER.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }

            System.err.println("Go！");
        }

        public static void main(String[] args) {
            CyclicBarrier CYCLIC_BARRIER = new CyclicBarrier(3);
            ExecutorService executorService = Executors.newFixedThreadPool(3);
            executorService.execute(new Runner(CYCLIC_BARRIER, "1号"));
            executorService.execute(new Runner(CYCLIC_BARRIER, "2号"));
            executorService.execute(new Runner(CYCLIC_BARRIER, "2号"));
            executorService.shutdown();
        }
    }
}
输出：
1号	准备好了
2号	准备好了
2号	准备好了
Go！
Go！
Go！

案例2

public class TestCyclicBarrier {

    private static final int THREAD_NUM = 5;
    
    public static class WorkerThread implements Runnable{

        CyclicBarrier barrier;
        
        public WorkerThread(CyclicBarrier b){
            this.barrier = b;
        }
        
        @Override
        public void run() {
            // TODO Auto-generated method stub
            try{
                System.out.println("Worker's waiting");
                //线程在这里等待，直到所有线程都到达barrier。
                barrier.await();
                System.out.println("ID:"+Thread.currentThread().getId()+" Working");
            }catch(Exception e){
                e.printStackTrace();
            }
        }
        
    }
    
    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        CyclicBarrier cb = new CyclicBarrier(THREAD_NUM, new Runnable() {
            //当所有线程到达barrier时执行
            @Override
            public void run() {
                // TODO Auto-generated method stub
                System.out.println("Inside Barrier");
                
            }
        });
        
        for(int i=0;i<THREAD_NUM;i++){
            new Thread(new WorkerThread(cb)).start();
        }
    }

}
/*
以下是输出：
Worker's waiting
Worker's waiting
Worker's waiting
Worker's waiting
Worker's waiting
Inside Barrier
ID:12 Working
ID:8 Working
ID:11 Working
ID:9 Working
ID:10 Working
*/

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