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Lazy Alternatives - LazyAndWeak and BackgroundLoader

, 1 Dec 2011 CPOL
This article will present two alternatives to Lazy.
LazyAlternatives
LazyAlternatives.suo
LazyAlternativesSample
Properties
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.Collections.Generic;
using System.Threading;
using Pfz.Caching;

namespace Pfz.Threading
{
	/// <summary>
	/// Base class for DiposableThreadLocal and its generic version.
	/// </summary>
	public class BaseDisposableThreadLocal:
		IDisposable,
		IGarbageCollectionAware
	{
		internal readonly object _lock = new object();
		internal Dictionary<Thread, DisposeAssurer> _dictionary = new Dictionary<Thread, DisposeAssurer>(ReferenceComparer.Instance);

		internal BaseDisposableThreadLocal()
		{
			GCUtils.RegisterForCollectedNotification(this);
		}

		/// <summary>
		/// Releases the values used by all threads that accessed this thread-local variable.
		/// </summary>
		public void Dispose()
		{
			GCUtils.UnregisterFromCollectedNotification(this);

			Dictionary<Thread, DisposeAssurer> dictionary;
			lock(_lock)
			{
				dictionary = _dictionary;

				if (dictionary == null)
					return;

				_dictionary = null;
			}

			foreach(var value in dictionary.Values)
				if (value != null)
					value.Dispose();
		}
		void IGarbageCollectionAware.OnCollected()
		{
			int count = 0;
			KeyValuePair<Thread, DisposeAssurer>[] toRemove;
			lock(_lock)
			{
				var dictionary = _dictionary;
				if (dictionary == null)
				{
					GCUtils.UnregisterFromCollectedNotification(this);
					return;
				}

				try
				{
					toRemove = new KeyValuePair<Thread, DisposeAssurer>[dictionary.Count];
					foreach(var pair in dictionary)
					{
						var thread = pair.Key;
						
						if (!thread.IsAlive)
						{
							toRemove[count] = pair;
							count++;
						}
					}
				}
				catch
				{
					return;
				}

				for(int i=0; i<count; i++)
					dictionary.Remove(toRemove[i].Key);
			}

			for(int i=0; i<count; i++)
				toRemove[i].Value.Dispose();
		}

		internal IDisposable _GetOrCreateValue(Func<IDisposable> valueFactory)
		{
			if (valueFactory == null)
				throw new ArgumentNullException("valueFactory");

			var thread = Thread.CurrentThread;

			if (thread.IsThreadPoolThread)
				throw new InvalidOperationException("Can't create ThreadLocal variables for .Net default ThreadPool. Such threads are revived with all their variables.");

			lock(_lock)
			{
				var dictionary = _dictionary;
				if (dictionary == null)
					throw new ObjectDisposedException(GetType().FullName);

				DisposeAssurer disposeCaller;
				if (_dictionary.TryGetValue(thread, out disposeCaller))
					return disposeCaller.Value;

				var result = valueFactory();
				disposeCaller = DisposeAssurer.Create(result);
				_dictionary.Add(thread, disposeCaller);
				return result;
			}
		}
		internal IDisposable _Value
		{
			get
			{
				var thread = Thread.CurrentThread;
				lock(_lock)
				{
					var dictionary = _dictionary;
					if (dictionary == null)
						throw new ObjectDisposedException(GetType().FullName);

					DisposeAssurer disposeCaller;
					if (_dictionary.TryGetValue(thread, out disposeCaller))
						return disposeCaller.Value;

					return null;
				}
			}
			set
			{
				var thread = Thread.CurrentThread;

				if (thread.IsThreadPoolThread)
					throw new InvalidOperationException("Can't create ThreadLocal variables for .Net default ThreadPool. Such threads are revived with all their variables.");

				DisposeAssurer oldDisposeCaller;

				lock(_lock)
				{
					var dictionary = _dictionary;
					if (dictionary == null)
						throw new ObjectDisposedException(GetType().FullName);

					_dictionary.TryGetValue(thread, out oldDisposeCaller);

					if (value == null)
						_dictionary.Remove(thread);
					else
					{
						DisposeAssurer newDisposeCaller = DisposeAssurer.Create(value);
						_dictionary[thread] = newDisposeCaller;
					}
				}

				if (oldDisposeCaller != null)
					oldDisposeCaller.Dispose();
			}
		}
	}
}

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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
Engineer Microsoft Corporation
United States United States
I started to program computers when I was 11 years old, as a hobbyist, 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 their work easier, faster and with less errors.

Now I just started working as a Senior Software Engineer at Microsoft.

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, 2015 & 2016
Microsoft MVP 2013-2014 (now I work at Microsoft so I can't be a Microsoft MVP anymore)

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