学步园

package com.entel.research;

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

public class JunitSemaphore
{
	public static void main(String[] args)
	{
		ExecutorService executorService = Executors.newCachedThreadPool();
		final Semaphore semaphore = new Semaphore(5);
		
		for(int i=0;i<5;i++)
		{
			Runnable runnable = new Runnable()
			{
				@Override
				public void run()
				{
					try
					{
						semaphore.acquire();
						
						System.out.println("线程" + Thread.currentThread().getName() + 
								"进入，当前已有" + (3-semaphore.availablePermits()) + "个并发");
						
						Thread.sleep(3000);
						
						System.out.println("线程" + Thread.currentThread().getName() + 
								"即将离开");					
						semaphore.release();
						//下面代码有时候执行不准确，因为其没有和上面的代码合成原子单元
						System.out.println("线程" + Thread.currentThread().getName() + 
								"已离开，当前已有" + (3-semaphore.availablePermits()) + "个并发");
					}
					catch (Exception e)
					{
						e.printStackTrace();
					}
				}
			};
			executorService.execute(runnable);
		}
	}
}