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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.Diagnostics.CodeAnalysis;

namespace Pfz.Threading
{
	/// <summary>
	/// This class is useful if you need to implement the dispose pattern
	/// in a thread-safe manner.
	/// It guarantees that dispose will be called only once, even if many 
	/// threads try to call Dispose at once. In your code, you must lock 
	/// DisposeLock, check if the object is disposed and call anything that 
	/// must be guaranteed to run before dispose inside the lock block.
	/// </summary>
	public abstract class ThreadSafeDisposable:
		IAdvancedDisposable
	{
		#region Destructor
			/// <summary>
			/// Calls Dispose(false);
			/// </summary>
			~ThreadSafeDisposable()
			{
				Dispose(false);
			}
		#endregion
		#region Dispose
			#region Without parameters
				/// <summary>
				/// Calls Dispose(true) to release all resources.
				/// Guarantees that only a single call to Dispose(true) is done 
				/// even if  this method is invoked multiple times or by many 
				/// different threads at the same time.
				/// </summary>
				[SuppressMessage("Microsoft.Design", "CA1063:ImplementIDisposableCorrectly")]
				public void Dispose()
				{
					if (_wasDisposed)
						return;

					bool mustDispose = false;
					try
					{
						lock(_disposeLock)
						{
							if (_wasDisposed)
								return;

							try
							{
							}
							finally
							{
								_wasDisposed = true;
								mustDispose = true;
							}
						}
					}
					finally
					{
						if (mustDispose)
						{
							Dispose(true);
							GC.SuppressFinalize(this);
						}
					}
				}
			#endregion
			#region Protected - bool disposing
				/// <summary>
				/// Implement this method to release all resources used by this object.
				/// </summary>
				/// <param name="disposing">
				/// This parameter is true if it was called by a user call to Dispose(),
				/// and false if it was called by a destructor. If false, you don't need
				/// to release managed resources (in general, you don't need to set any
				/// variables to null or even reference other objects, only freeing 
				/// "unsafe" pointers).
				/// </param>
				protected virtual void Dispose(bool disposing)
				{
				}
			#endregion
		#endregion
		
		#region Properties
			#region WasDisposed
				private volatile bool _wasDisposed;
				
				/// <summary>
				/// Returns true if a call to Dispose was already done (or still in
				/// progress in another thread). If it is true, you can't continue
				/// to use your object.
				/// </summary>
				public bool WasDisposed
				{
					get
					{
						return _wasDisposed;
					}
				}
			#endregion
			#region DisposeLock
				private readonly object _disposeLock = new object();
				
				/// <summary>
				/// This is the lock used during dispose. You may want to lock
				/// some of your code against dispose using this lock.
				/// The preferred way to use it is: 
				///	lock(DisposeLock)
				///	{
				///		CheckUndisposed();
				///		
				///		... your protected code here ...
				///	}
				/// </summary>
				internal protected object DisposeLock
				{
					get
					{
						return _disposeLock;
					}
				}
			#endregion
		#endregion
		#region Methods
			#region CheckUndisposed
				/// <summary>
				/// Checks if the objects is disposed. If it is, throws an 
				/// ObjectDisposedException. Call this as the first method inside a 
				/// lock(DisposeLock)
				///	{
				///		CheckUndisposed(); 
				///		... your protected code here ...
				///	}
				/// 
				/// or simple call it without any lock if you only want to throw
				/// an exception if the object is already disposed but such a call
				/// is read-only.
				/// </summary>
				protected void CheckUndisposed()
				{
					if (_wasDisposed)
						throw new ObjectDisposedException(GetType().FullName);
				}
			#endregion
		#endregion
	}
}

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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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