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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 Pfz.Threading;
using Pfz.Remoting;
using System.Threading;

namespace Pfz.Collections
{
	/// <summary>
	/// This class is responsible for distributing a single enumerator
	/// among many enumerator readers, considering such readers can
	/// "loose" some of the items.
	/// This is useful for senting, for example, web-cam frames. A high-speed
	/// client can receive all frames, while a slow client can receive frame
	/// 1, then frame 6, frame 12... but will still receive the "most recent"
	/// frames.
	/// You can inherit this class the the MultiClientEnumerator themselves
	/// if you must only send the difference between frames.
	/// </summary>
	/// <typeparam name="T">
	/// The type of the item that the original enumerator returns.
	/// </typeparam>
	public class EnumeratorDistributor<T>:
		ThreadSafeExceptionAwareDisposable
	where
		T: class
	{
		internal AutoTrimHashSet<EnumeratorDistributorClient<T>> _clientEnumerators = new AutoTrimHashSet<EnumeratorDistributorClient<T>>();
	
		/// <summary>
		/// Creates a new Distributor over the given real enumerator.
		/// </summary>
		public EnumeratorDistributor(IFastEnumerator<T> baseEnumerator)
		{
			if (baseEnumerator == null)
				throw new ArgumentNullException("baseEnumerator");
			
			BaseEnumerator = baseEnumerator;
			
			UnlimitedThreadPool.Run(_KeepReading);
		}
		
		/// <summary>
		/// Disposes the base enumerator and the clients actually connected.
		/// </summary>
		protected override void Dispose(bool disposing)
		{
			if (disposing)
			{
				var baseEnumerator = BaseEnumerator;
				if (baseEnumerator != null)
				{
					BaseEnumerator = null;
					baseEnumerator.Dispose();
				}

				lock(DisposeLock)
					Monitor.PulseAll(DisposeLock);

				/*var clientEnumerators = _clientEnumerators;
				if (clientEnumerators != null)
				{
					_clientEnumerators = null;

					lock(DisposeLock)
						foreach(var client in clientEnumerators)
							client.Dispose();

					clientEnumerators.Dispose();
				}*/

				_actualValue = null;
				
				var disposedEvent = Disposed;
				if (disposedEvent != null)
					disposedEvent(this, EventArgs.Empty);
			}
			
			base.Dispose(disposing);
		}
		
		/// <summary>
		/// Gets the BaseEnumerator used by this distributor.
		/// </summary>
		public IFastEnumerator<T> BaseEnumerator { get; private set; }
		
		/// <summary>
		/// Called when this object is disposed.
		/// </summary>
		public event EventHandler Disposed;
		
		private volatile T _actualValue;
		
		/// <summary>
		/// Gets the Actual value without waiting.
		/// </summary>
		public T ActualValue
		{
			get
			{
				return _actualValue;
			}
		}
		
		private void _KeepReading()
		{
			using(new AllowSyncRemoting(true))
			{
				try
				{
					var baseEnumerator = BaseEnumerator;
					while(true)
					{
						if (WasDisposed)
							return;
					
						var actualValue = baseEnumerator.GetNext();
						_actualValue = actualValue;
					
						if (actualValue == null)
						{
							Dispose();
							return;
						}

						lock(DisposeLock)
							Monitor.PulseAll(DisposeLock);
    						//foreach(var client in _clientEnumerators)
	    						//client._autoResetEvent.Set();
					}
				}
				catch(Exception exception)
				{
					Dispose(exception);
				}
			}
		}
		
		/// <summary>
		/// Creates a client for this enumerator.
		/// Inheritors can initialize additional information before returning 
		/// the enumerator client to you.
		/// </summary>
		public virtual EnumeratorDistributorClient<T> CreateClient()
		{
			return new EnumeratorDistributorClient<T>(this);
		}
	}
}

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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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