仿真跑马的代码，还挺有意思的（P724）

package thread;

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

public class Horse implements Runnable {
    private static int counter = 0;
    private final int id = counter++;
    private int strides = 0;
    private static Random rand = new Random(47);
    private static CyclicBarrier barrier;

    public Horse(CyclicBarrier b) {
        barrier = b;
    }

    public synchronized int getStrides() {
        return strides;
    }

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

        } catch (BrokenBarrierException e) {
            throw new RuntimeException(e);
        }
    }

    public String toString() {
        return "Horse" + id + " ";
    }
    public String tracks(){
        StringBuilder s = new StringBuilder();
        for(int i = 0;i < getStrides();i++) s.append("*");
        s.append(id);
        return s.toString();
    }
}

package thread;

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

public class HorseRace {
    static final int FINISH_LINE = 20;
    private List<Horse> horses = new ArrayList<Horse>();
    private ExecutorService exec = Executors.newCachedThreadPool();
    private CyclicBarrier barrier;

    public HorseRace(int nHorses, final int pause) throws Exception {
        barrier = new CyclicBarrier(nHorses, new Runnable() {
            public void run() {
                StringBuilder s = new StringBuilder();
                for (int i = 0; i < FINISH_LINE; i++) s.append("=");
                System.out.println(s);
                for (Horse horse : horses) {
                    System.out.println(horse.tracks());
                    try {
                        TimeUnit.MILLISECONDS.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                for (Horse horse : horses)
                    if (horse.getStrides() >= FINISH_LINE) {
                        System.out.println(horse + " won!");
                        exec.shutdownNow();
                        return;
                    }
                try {
                    TimeUnit.SECONDS.sleep(5);
                } catch (InterruptedException e) {
                    System.out.println("barrier-action sleep interrupted");
                }
            }
        });
        for(int i = 0;i < nHorses;i++){
            Horse horse = new Horse(barrier);
            horses.add(horse);
            exec.execute(horse);
        }
    }
    public static void main(String[] args){
        int nHorses = 7;
        int pause = 200;
        if(args.length > 0){
            int n = new Integer(args[0]);
            nHorses = n > 0 ? n: nHorses;
        }
        if(args.length > 1){
            int p = new Integer(args[1]);
            pause = p > -1 ? p : pause;
        }
        try {
            new HorseRace(nHorses,pause);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}