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Lazy Alternatives - LazyAndWeak and BackgroundLoader

, 1 Dec 2011
This article will present two alternatives to Lazy.
LazyAlternatives.zip
LazyAlternatives
LazyAlternatives.suo
LazyAlternativesSample
Properties
Settings.settings
Pfz
Caching
Collections
DataTypes
DynamicObjects
Internal
Extensions
Factoring
Pfz.csproj.user
Pfz.Phone.csproj.user
Pfz.ruleset
Pfz.Silverlight.csproj.user
Pfz.snk
Pfz.suo
PhoneSpecific
Properties
Remoting
Instructions
Internal
Serializers
Udp
Serialization
BinaryBuiltIn
Threading
Contexts
Disposers
Unsafe
using System;
using System.IO.MemoryMappedFiles;
using System.Threading;
using Pfz.Caching;
using Pfz.Threading;

namespace Pfz.Remoting
{
	/// <summary>
	/// Creates a Listener using MemoryMappedFiles (local-only, but very fast).
	/// </summary>
	public sealed class MmfChannellerListener:
		ThreadSafeDisposable,
		IChannellerListener
	{
		private MemoryMappedFile _file;
		private MemoryMappedViewAccessor _accessor;
		private Mutex _mutex;

		private EventWaitHandle _requestEvent;
		private EventWaitHandle _resultEvent;
		private ManualResetEvent _mreDisposed;
		private WaitHandle[] _waitHandles;

		/// <summary>
		/// Creates a new listener with the given name.
		/// </summary>
		public MmfChannellerListener(string name)
		{
			if (name == null)
				throw new ArgumentNullException("name");

			try
			{
				bool createdNew;
				_mutex = new Mutex(false, "Pfz.Remoting.MmfListener.Mutex:" + name, out createdNew);
				if (!createdNew)
					throw new RemotingException("The given listener name is already used.");

				_requestEvent = new EventWaitHandle(false, EventResetMode.AutoReset, "Pfz.Remoting.MmfListener.RequestEvent:" + name, out createdNew);
				if (!createdNew)
					throw new RemotingException("The given listener name is already used.");

				_resultEvent = new EventWaitHandle(false, EventResetMode.AutoReset, "Pfz.Remoting.MmfListener.ResultEvent:" + name, out createdNew);
				if (!createdNew)
					throw new RemotingException("The given listener name is already used.");

				_file = MemoryMappedFile.CreateNew("Pfz.Remoting.MmfListener.MemoryMappedFile:" + name, sizeof(long));

				_accessor = _file.CreateViewAccessor();

				_mreDisposed = new ManualResetEvent(false);
				_waitHandles= new WaitHandle[2];
				_waitHandles[0] = _mreDisposed;
				_waitHandles[1] = _requestEvent;
			}
			catch
			{
				Dispose();
				throw;
			}
		}

		/// <summary>
		/// Releases all the resources used by this object.
		/// </summary>
		protected override void Dispose(bool disposing)
		{
			if (disposing)
			{
				var mreDisposed = _mreDisposed;
				if (mreDisposed != null)
					mreDisposed.Set();

				Disposer.Dispose(ref _requestEvent);
				Disposer.Dispose(ref _resultEvent);
				Disposer.Dispose(ref _mutex);
				Disposer.Dispose(ref _accessor);
				Disposer.Dispose(ref _file);
			}

			base.Dispose(disposing);
		}

		/// <summary>
		/// Tries to accept a new channeller.
		/// </summary>
		/// <returns></returns>
		public MmfChanneller TryAccept()
		{
			CheckUndisposed();

			int index = WaitHandle.WaitAny(_waitHandles);
			if (index == 0)
			{
				var mreDisposed = _mreDisposed;
				if (mreDisposed != null)
				{
					_mreDisposed = null;
					mreDisposed.Dispose();
				}

				return null;
			}

			long newId = TicksOrIncrement.GetNext();

			lock(DisposeLock)
			{
				if (WasDisposed)
				{
					var mreDisposed = _mreDisposed;
					if (mreDisposed != null)
					{
						_mreDisposed = null;
						mreDisposed.Dispose();
					}

					return null;
				}

				var result = new MmfChanneller(newId, true);
				_accessor.Write(0, newId);
				_resultEvent.Set();
				return result;
			}
		}

		IChanneller IChannellerListener.TryAccept()
		{
			return TryAccept();
		}
	}
}

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About the Author

Paulo Zemek
Architect
Canada Canada
I started to program computers when I was 11 years old, as a hobbist, programming in AMOS Basic and Blitz Basic for Amiga.
At 12 I had my first try with assembler, but it was too difficult at the time. Then, in the same year, I learned C and, after learning C, I was finally able to learn assembler (for Motorola 680x0).
Not sure, but probably between 12 and 13, I started to learn C++. I always programmed "in an object oriented way", but using function pointers instead of virtual methods.
 
At 15 I started to learn Pascal at school and to use Delphi. At 16 I started my first internship (using Delphi). At 18 I started to work professionally using C++ and since then I've developed my programming skills as a professional developer in C++ and C#, generally creating libraries that help other developers do they work easier, faster and with less errors.
 
Want more info or simply want to contact me?
Take a look at: http://paulozemek.azurewebsites.net/
Or e-mail me at: paulozemek@outlook.com
 
Codeproject MVP 2012
Microsoft MVP 2013

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