Click here to Skip to main content
Click here to Skip to main content
Articles » Languages » C# » General » Downloads
 
Add your own
alternative version

Tagged as

Lazy Alternatives - LazyAndWeak and BackgroundLoader

, 1 Dec 2011 CPOL
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.Collections;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Runtime.Serialization;
using Pfz.Threading;

namespace Pfz.Caching
{
	/// <summary>
	/// HashSet class which allows items to be collected.
	/// </summary>
	[Serializable]
	public class WeakHashSet<T>:
		ReaderWriterSafeDisposable,
		IEnumerable<T>,
		ISerializable
	where
		T: class
	{
		private object _item;
		
		#region Private classes
			private sealed class _Values
			{
				public _Values(T item, int hashCode)
				{
					Handles = new GCHandle[1];
					Handles[0] = GCHandle.Alloc(item, GCHandleType.Weak);
					HashCode = hashCode;
					Count = 1;
				}
			
				public int HashCode;
				public int Count;
				public GCHandle[] Handles;

				internal void Add(object item)
				{
					if (Count == Handles.Length)
					{
						for (int i=0; i<Count; i++)
						{
							GCHandle handle = Handles[i];
							if (handle.Target == null)
							{
								handle.Target = item;
								return;
							}
						}
						
						Array.Resize(ref Handles, Count * 2);
					}
					
					try
					{
					}
					finally
					{
						Handles[Count] = GCHandle.Alloc(item, GCHandleType.Weak);
						Count++;
					}
				}
			}
		#endregion

		#region Constructor
			/// <summary>
			/// Creates a new instance of the WeakHashSet class.
			/// </summary>
			public WeakHashSet()
			{
				GCUtils.Collected += _Collected;
			}
		#endregion
		#region Dispose
			/// <summary>
			/// Releases all the GCHandles used internally.
			/// </summary>
			/// <param name="disposing"></param>
			protected override void Dispose(bool disposing)
			{
				if (disposing)
					GCUtils.Collected -= _Collected;
					
				_Dispose(_item);
			
				base.Dispose(disposing);
			}
			private static void _Dispose(object item)
			{
				if (item == null)
					return;
				
				var pair = item as object[];
				if (pair != null)
				{
					for (int i=0; i<16; i++)
						_Dispose(pair[i]);
					
					return;
				}
				
				_Values values = (_Values)item;
				for(int i=0; i<values.Count; i++)
					values.Handles[i].Free();
			}
		#endregion
		#region _Collected
			private void _Collected()
			{
				using(DisposeLock.WriteLock())
				{
					if (WasDisposed)
					{
						GCUtils.Collected -= _Collected;
						return;
					}
						
					_Collect(ref _item);
				}
			}
			private static bool _Collect(ref object item)
			{
				if (item == null)
					return true;
				
				var pair = item as object[];
				if (pair != null)
				{
					bool allCollected = true;
					for (int i=0; i<16; i++)
						allCollected &= _Collect(ref pair[i]);
					
					if (allCollected)
						item = null;
						
					return allCollected;
				}
				
				_Values values = (_Values)item;
				int count = values.Count;
				int countValid = 0;
				
				for (int i=0; i<count; i++)
					if (values.Handles[i].Target != null)
						countValid++;
						
				if (countValid == 0)
				{
					try
					{
					}
					finally
					{
						for (int i=0; i<count; i++)
							values.Handles[i].Free();
							
						item = null;
					}
					
					return true;
				}
				
				if (countValid < count)
				{
					GCHandle[] newArray = new GCHandle[countValid];
					int newArrayIndex = 0;
					try
					{
					}
					finally
					{
						for (int i=0; i<count; i++)
						{
							GCHandle handle = values.Handles[i];
							
							if (handle.Target == null)
								handle.Free();
							else
							{
								newArray[newArrayIndex] = handle;
								newArrayIndex++;
							}
						}
						
						values.Handles = newArray;
						values.Count = newArrayIndex;
					}
				}
				
				return false;
			}
		#endregion
		
		#region Clear
			/// <summary>
			/// Clears the contents of this weak hashset.
			/// </summary>
			public void Clear()
			{
				using(DisposeLock.WriteLock())
				{
					CheckUndisposed();

					try
					{
					}
					finally
					{
						_Dispose(_item);
						_item = null;
					}
				}
			}
		#endregion
		#region Add
			/// <summary>
			/// Tries to add an item in this hashset.
			/// Returns true if the item was added, or false if the item was
			/// already present.
			/// </summary>
			public bool Add(T item)
			{
				if (item == null)
					throw new ArgumentNullException("item");
				
				bool result = false;
				
				using(DisposeLock.WriteLock())
				{
					CheckUndisposed();
					
					int hashCode = item.GetHashCode();
						
					// 32-4: Reason - starting by the end (which changes more)
					// gives a better distribution.
					result = _Add(ref _item, hashCode, 32-4, item);
				}
				
				return result;
			}
		#endregion
		#region _Add
			private static bool _Add(ref object hashItem, int hashCode, int level, T item)
			{
				if (hashItem == null)
				{
					try
					{
					}
					finally
					{
						hashItem = new _Values(item, hashCode);
					}
					
					return true;
				}
				
				int index;
				var pair = hashItem as object[];
				if (pair != null)
				{
					index = (hashCode >> level) & 15;
					return _Add(ref pair[index], hashCode, level-4, item);
				}

				_Values values = (_Values)hashItem;
				if (hashCode == values.HashCode)
				{
					for (int i=0; i<values.Count; i++)
						if (item == values.Handles[i].Target)
							return false;

					values.Add(item);
					return true;
				}
				
				pair = new object[16];
				
				index = (values.HashCode >> level) & 15;
				pair[index] = values;
				hashItem = pair;
				
				index = (hashCode >> level) & 15;
				return _Add(ref pair[index], hashCode, level-4, item);
			}
		#endregion
		#region Contains
			/// <summary>
			/// Returns true if the given item is in this hashset, false otherwise.
			/// </summary>
			public bool Contains(T item)
			{
				if (item == null)
					throw new ArgumentNullException("item");
				
				using(DisposeLock.ReadLock())
				{
					CheckUndisposed();
					
					int hashCode = item.GetHashCode();
					int actualHashCode = hashCode;

					var hashItem = _item;
					while(true)
					{
						if (hashItem == null)
							return false;
							
						var pair = hashItem as object[];
						if (pair == null)
							break;
							
						int zeroOrOne = actualHashCode & 15;
						hashItem = pair[zeroOrOne];
							
						actualHashCode = actualHashCode >> 4;
					}
						
					_Values values = (_Values)hashItem;
					if (values.HashCode == hashCode)
						for(int i=0; i<values.Count; i++)
							if (item == values.Handles[i].Target)
								return true;
				}
				
				return false;
			}
		#endregion
		#region ToList
			/// <summary>
			/// Gets a list with all the non-collected items present in this
			/// hashset.
			/// </summary>
			/// <returns></returns>
			public List<T> ToList()
			{
				List<T> result = new List<T>();
				
				using(DisposeLock.ReadLock())
				{
					CheckUndisposed();
						
					_ToList(_item, result);
				}
				
				return result;
			}
		#endregion
		#region _ToList
			private static void _ToList(object hashItem, List<T> result)
			{
				if (hashItem == null)
					return;
				
				var pair = hashItem as object[];
				if (pair != null)
				{
					for (int i=0; i<16; i++)
						_ToList(pair[i], result);

					return;
				}

				_Values values = (_Values)hashItem;
				int count = values.Count;
				for (int i=0; i<count; i++)
				{
					GCHandle handle = values.Handles[i];
					object target = handle.Target;
					if (target != null)
						result.Add((T)target);
				}
			}
		#endregion
		#region Remove
			/// <summary>
			/// Removes the given item from this hashset.
			/// Returns a value indicating if the given item was in the hashset.
			/// </summary>
			public bool Remove(T item)
			{
				if (item == null)
					throw new ArgumentNullException("item");
				
				using(DisposeLock.WriteLock())
				{
					CheckUndisposed();
					
					int hashCode = item.GetHashCode();
					int actualHashCode = hashCode;

					var hashItem = _item;
					while(true)
					{
						if (hashItem == null)
							return false;
							
						var pair = hashItem as object[];
						if (pair == null)
							break;
							
						int zeroOrOne = actualHashCode & 15;
						hashItem = pair[zeroOrOne];
							
						actualHashCode = actualHashCode >> 4;
					}
						
					_Values values = (_Values)hashItem;
					if (values.HashCode == hashCode)
					{
						for(int i=0; i<values.Count; i++)
						{
							GCHandle handle = values.Handles[i];
								
							if (item == handle.Target)
							{
								handle.Target = null;
								return true;
							}
						}
					}
				}
				
				return false;
			}
		#endregion

		#region ISerializable Members
			/// <summary>
			/// Creates the class from serialization. At this level, does not read
			/// anything, as if everything was collected.
			/// </summary>
			protected WeakHashSet(SerializationInfo info, StreamingContext context)
			{
			}
			
			/// <summary>
			/// Does not add any items to the serialization info, as if everything
			/// was collected.
			/// </summary>
			protected virtual void GetObjectData(SerializationInfo info, StreamingContext context)
			{
				GCUtils.Collected += _Collected;
			}
			
			void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
			{
				GetObjectData(info, context);
			}
		#endregion
		#region IEnumerable<T> Members
			/// <summary>
			/// Gets an enumerator over the non-collected items in this hashset.
			/// </summary>
			public IEnumerator<T> GetEnumerator()
			{
				return ToList().GetEnumerator();
			}
		#endregion
		#region IEnumerable Members
			IEnumerator IEnumerable.GetEnumerator()
			{
				return GetEnumerator();
			}
		#endregion
	}
}

By viewing downloads associated with this article you agree to the Terms of Service and the article's licence.

If a file you wish to view isn't highlighted, and is a text file (not binary), please let us know and we'll add colourisation support for it.

License

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

Share

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 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.
 
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
Microsoft MVP 2013-2014

| Advertise | Privacy | Terms of Use | Mobile
Web02 | 2.8.150123.1 | Last Updated 1 Dec 2011
Article Copyright 2011 by Paulo Zemek
Everything else Copyright © CodeProject, 1999-2015
Layout: fixed | fluid