使用Java里的Semaphore信号量模拟顾客逛Coach店

    Coach店一般只允许保持不超过某个特定数量的顾客在店里，其余的顾客要在店外等候，直到店里有顾客出来才允许进入，Java中的Semaphore信号量的用法和这个场景非常相似，下面使用Semaphore仿真顾客逛Coach店的场景。
(1)顾客类Guest：

package coachStore;

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

public class Guest implements Runnable
{
	//Coach店一次允许进入的顾客数量
	private static final int SIZE = 10;
	private static int count = 0;
	private int id = count++;
	//允许SIZE个顾客同时访问的信号量
	private static Semaphore room = new Semaphore(SIZE, true);
	private int shoppingTime;
	
	public Guest(int shoppingTime)
	{
		this.shoppingTime = shoppingTime;
	}
	public void run()
	{
		try 
		{
			System.out.println("Guest " + id + " is waiting for entering the store");
			//顾客等待进入Coach店，如果店里的顾客已满，则等待(阻塞)
			room.acquire();
			System.out.println("Guest " + id + " entered the store and started to look around");
			//线程睡眠以模拟顾客在店里逛的动作
			TimeUnit.SECONDS.sleep(shoppingTime);
			//顾客离开时需要签离，释放一个位置
			room.release();
			System.out.println("Guest " + id + " stayed for " + shoppingTime + " seconds and left");
		} 
		catch (InterruptedException e)
		{
			e.printStackTrace();
		}
	}
}

(2)main类：

package coachStore;

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

public class CoachStoreDemo 
{
	//所有顾客的数量
	final static int GUEST_QUANTITY = 100;
	private static Random rand = new Random(47);
	public static void main(String[] args)
	{
		ExecutorService exec = Executors.newCachedThreadPool();
		for(int i = 0; i < GUEST_QUANTITY; i++)
		{
			//随机生成一个0到10之间的数字表示顾客在店里逗留的时间，启动一个顾客线程
			exec.execute(new Guest(rand.nextInt(10)));
		}
	}
	
}