ObjectPool, C# - rextester

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

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

namespace Rextester
{
    class PoolResource : IDisposable
    {
        public void Dispose()
        {
            Console.WriteLine("Pool Resource Dispose Method called");
        }
    }
    
    class ObjectPool<T>:IDisposable where T:IDisposable,new()
    {
        private class CacheEntry<U> : IDisposable where U:IDisposable
        {
            public bool InUse{get; set;}
            public U Resource{get; private set;}
            
            public CacheEntry(U resource)
            {
                InUse = false;
                Resource = resource;
            }
            
            public void Dispose()
            {
                if(Resource!=null)
                {
                    Resource.Dispose();
                }
            }
        }
        
        private List<CacheEntry<T>> _entries = new List<CacheEntry<T>>();
        private int _capacity;
        
        public ObjectPool(int capacity)
        {
            _capacity = capacity;
        }
        
        public T AcquireResource()
        {
            foreach(var entry in _entries)
            {
                if(!entry.InUse)
                {
                    entry.InUse = true;
                    return entry.Resource;
                }
            }
            
            if(_entries.Count < _capacity)
            {
                var resource = new T();
                var cacheEntry = new CacheEntry<T>(resource);
                cacheEntry.InUse = true;
                _entries.Add(cacheEntry);
                return resource;
            }
            
            throw new InvalidOperationException();
        }
        
        public void ReleaseResource(T resource)
        {
            bool found = false;
            foreach(var entry in _entries)
            {
                if(entry.Resource.GetHashCode() == resource.GetHashCode())
                {
                    entry.InUse = false;
                    found = true;
                    break;
                }
            }
            
            if(!found)
            {
                throw new InvalidOperationException();
            }
        }
        
        public void Dispose()
        {
            Console.WriteLine("Object Pool Dispose called!");
            foreach(var d in _entries)
            {
                if(d != null)
                {
                    d.Dispose();
                }
            }
        }
    }
    
    public class Program
    {
        public static void Main(string[] args)
        {
            var objectPool = new ObjectPool<PoolResource>(2);
            using(objectPool)
            {
                var first = objectPool.AcquireResource();
                Console.WriteLine(first.GetHashCode());
                
                var second = objectPool.AcquireResource();
                Console.WriteLine(second.GetHashCode());
                
                try
                {
                    var third = objectPool.AcquireResource();
                    Console.WriteLine(third.GetHashCode());
                }
                catch(Exception ex)
                {
                    Console.WriteLine(ex.ToString());
                }
                
                objectPool.ReleaseResource(second);
                try
                {
                    var fourth = objectPool.AcquireResource();
                    Console.WriteLine(fourth.GetHashCode());
                }
                catch(Exception ex)
                {
                    Console.WriteLine(ex.ToString());
                }
            }
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,2 sec, absolute running time: 0,14 sec, cpu time: 0,12 sec, average memory usage: 14 Mb, average nr of threads: 3, absolute service time: 0,38 sec