併發-新類庫中的構件 CyclicBarrier

CyclicBarrier

• 適用於如下情況：創建一組任務，並行執行工作，然後在進行下一個步驟之前等待，直至所有任務都完成（看起來有些像join（））。它使得所有的並行任務都將在柵欄處列隊，而CyclicBarrier可以多次重用。
• 賽馬遊戲

package com21concurrent;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.*;

/**
 * Created by Panda on 2018/6/1.
 */
//測試CyclicBarrier
class Horse implements Runnable{
    private static int counter=0;
    private final int id=counter++;
    private int strides=0;
    private static Random random=new Random(47);
    private static CyclicBarrier cyclicBarrier;

    public Horse(CyclicBarrier cyclicBarrier) {
        this.cyclicBarrier=cyclicBarrier;
    }
    public synchronized int getStrides(){return strides;}

    @Override
    public void run() {
        try{
            while (!Thread.interrupted()){
                synchronized (this){
                    strides+=random.nextInt(3);
                }
                cyclicBarrier.await();
            }
        }catch (InterruptedException e){

        }catch (BrokenBarrierException e){
            throw new RuntimeException();
        }
    }
    public String toString(){return "Horse "+id+" ";}
    public String tracks(){
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = 0; i < getStrides(); i++) {
            stringBuilder.append("*");
        }
        stringBuilder.append(id);
        return stringBuilder.toString();
    }
}
public class HorseRace {
    static final int FINISH_LINE=75;
    private List<Horse> horses=new ArrayList<>();
    private ExecutorService executorService = Executors.newCachedThreadPool();
    private CyclicBarrier cyclicBarrier;
    public HorseRace(int nHorses,final int pause){
        cyclicBarrier=new CyclicBarrier(nHorses, new Runnable() {
            @Override
            public void run() {
                StringBuilder stringBuilder= new StringBuilder();
                for (int i = 0; i <FINISH_LINE ; i++) {
                    stringBuilder.append("=");
                }
                System.out.println(stringBuilder);
                for (Horse horse:horses){
                    System.out.println(horse.tracks());
                }
                for(Horse horse:horses){
                    if(horse.getStrides()>=FINISH_LINE){
                        System.out.println(horse+" won");
                        executorService.shutdownNow();
                        return;
                    }
                }

                try{
                    TimeUnit.MILLISECONDS.sleep(pause);
                }catch (InterruptedException e){
                    System.out.println("barrier-action sleep interruptedException");
                }
            }
        });
        for (int i = 0; i <nHorses ; i++) {
            Horse horse = new Horse(cyclicBarrier);
            horses.add(horse);
            executorService.execute(horse);
        }
    }

    public static void main(String[] args) {
        int nHorse=7;
        int pause=200;
        if(args.length>0){
            int n=new Integer(args[0]);
            nHorse=n>0?n:nHorse;
        }
        if(args.length>1){
            int p=new Integer(args[1]);
            pause=p>-1?p:pause;
        }
        new HorseRace(nHorse,pause);
    }
}