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CSharp · Console

/Program.cs

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;
using System.Net;

namespace Rextester
{
    public class Program
    {
        public class SimpleLazy<T> where T : class
		{
			private readonly Func<T> valueFactory;
			private T instance;
			private readonly object locker = new object();

			public SimpleLazy(Func<T> valueFactory)
			{
				this.valueFactory = valueFactory;
				this.instance = null;
			}

			public T Value
			{
				get
				{
					lock (locker)
						return instance ?? (instance = valueFactory());
				}
			}
		}

        public class LightsaberProvider
        {
            private static int _firstTime = 1;

            public LightsaberProvider()
            {
                Console.WriteLine("LightsaberProvider ctor");
            }

            public string GetFor(string jedi)
            {
                Console.WriteLine("LightsaberProvider.GetFor jedi: {0}", jedi);

                Thread.Sleep(100);
                if (jedi == "2" && 1 == Interlocked.Exchange(ref _firstTime, 0))
                {
                    throw new Exception("Dark side happened...");
                }

                Thread.Sleep(100);
                return string.Format("Lightsaver for: {0}", jedi);
            }
        }

        public class LightsabersCache
        {
            private readonly LightsaberProvider _lightsaberProvider;
            private readonly ConcurrentDictionary<string, SimpleLazy<string>> _producedLightsabers;

            public LightsabersCache(LightsaberProvider lightsaberProvider)
            {
                _lightsaberProvider = lightsaberProvider;
                _producedLightsabers = new ConcurrentDictionary<string, SimpleLazy<string>>();
            }

            public string GetLightsaber(string jedi)
            {
                SimpleLazy<string> result;
                if (!_producedLightsabers.TryGetValue(jedi, out result))
                {
                    result = _producedLightsabers.GetOrAdd(jedi, key => new SimpleLazy<string>(() =>
                    {
                        Console.WriteLine("Lazy Enter");
                        var light = _lightsaberProvider.GetFor(jedi);
                        Console.WriteLine("Lightsaber produced");
                        return light;
                    }));
                }
                return result.Value;
            }
        }

        public static void Main(string[] args)
        {
            Test();
            Console.WriteLine("Maximum 1 'Dark side happened...' strings on the console there should be. No more, no less.");
            Console.WriteLine("Maximum 5 lightsabers produced should be. No more, no less.");
        }

        private static void Test()
        {
            var cache = new LightsabersCache(new LightsaberProvider());

            Parallel.For(0, 15, t =>
            {
                for (int i = 0; i < 10; i++)
                {
                    try
                    {
                        var result = cache.GetLightsaber((t % 5).ToString());
                    }
                    catch (Exception e)
                    {
                        Console.WriteLine(e.Message);
                    }
                }
            });
        }
    }
}