using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace SemaphoreExample
{
    class SharedResource
    {
        public bool Used { get; set; }
        public object ResObject { get; set; }
    }

    class Program
    {
        static SharedResource[] resources;
        static Semaphore sem;

        static SharedResource GetResource()
        {
            sem.WaitOne();
            SharedResource res = resources.First(x => !x.Used);
            res.Used = true;
            Console.WriteLine("Thread {0} was granted a resource", Thread.CurrentThread.Name);
            return res;
        }

        static void FreeResource(SharedResource res)
        {
            if (res.Used)
            {
                res.Used = false;
                int i = sem.Release();
                Console.WriteLine("Thread {0} freed a resource, {1} resources was free", Thread.CurrentThread.Name, i);
            }
        }

        static void DoWork()
        {
            while (true)
            {
                SharedResource res = GetResource();
                Thread.Sleep(1000);
                FreeResource(res);
                Thread.Sleep(1000);
            }
        }

        static void Main(string[] args)
        {
            resources = new SharedResource[3] { new SharedResource(), new SharedResource(), new SharedResource() };
            sem = new Semaphore(3,3);

            for (int i =1; i <=6; i++)
            {
                Thread p = new Thread(DoWork);
                p.Name = i.ToString();
                p.Start();
                Thread.Sleep(100);
            }
        }
    }
}