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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.Threading;
using Pfz.Threading;

namespace Pfz.Collections
{
	/// <summary>
	/// This class connects to a EnumeratorDistributor and is able
	/// to use GetNext to get a next frame when one is available, while it is 
	/// also able to "loose" values if the real enumerator is running faster 
	/// than this client. This is useful when getting frames from a web-cam, 
	/// for example.
	/// </summary>
	public class EnumeratorDistributorClient<T>:
		ThreadSafeDisposable,
		IFastEnumerator<T>
	where
		T: class
	{
		#region Constructor
			/// <summary>
			/// Creates a new multi-client enumerator connected to the given distributor.
			/// </summary>
			public EnumeratorDistributorClient(EnumeratorDistributor<T> distributor)
			{
				if (distributor == null)
					throw new ArgumentNullException("distributor");
				
				Distributor = distributor;
				lock(distributor.DisposeLock)
				{
					distributor.CheckUndisposed();
					distributor._clientEnumerators.Add(this);
				}
			}
		#endregion
		#region Dispose
			/// <summary>
			/// Releases the resources used by this enumerator and removes it from
			/// the distributor list.
			/// </summary>
			protected override void Dispose(bool disposing)
			{
				if (disposing)
				{
					var distributor = Distributor;
					if (distributor != null)
					{
						Distributor = null;
						
                        lock(distributor.DisposeLock)
						{
							if (!distributor.WasDisposed)
							{
								var clientEnumerators = distributor._clientEnumerators;
								if (clientEnumerators != null)
									clientEnumerators.Remove(this);

								Monitor.PulseAll(distributor.DisposeLock);
							}
						}
					}
				}
			
				base.Dispose(disposing);
			}
		#endregion
		
		#region Property - Distributor
			/// <summary>
			/// Gets the Distributor used by this enumerator.
			/// </summary>
			public EnumeratorDistributor<T> Distributor { get; private set; }
		#endregion
		#region Method - GetNext
			private T _lastValue;

			/// <summary>
			/// Gets the actual value of the distributor or waits until a new
			/// value is available.
			/// </summary>
			public virtual T GetNext()
			{
                var distributor = Distributor;
                if (distributor == null)
                    return null;

                lock(distributor.DisposeLock)
				{
					while(true)
					{
						if (distributor.WasDisposed)
						{
							var disposeException = distributor.DisposeException;
							if (disposeException != null)
								throw new ObjectDisposedException("This enumerator was disposed by an exception in its distributor.", disposeException);

							return null;
						}

						var result = distributor.ActualValue;
						if (object.Equals(result, _lastValue))
						{
							Monitor.Wait(distributor.DisposeLock);
							continue;
						}

						_lastValue = result;
						return result;
					}
				}
			}
		#endregion
	}
}

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This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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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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