feat: Initial commit of WeakKeyDictionary for keeping caches of items that can not invalidate themselves

ICD.Common.Utils/Collections/WeakKeyDictionary.cs

@@ -0,0 +1,283 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using ICD.Common.Properties;
+using ICD.Common.Utils.Extensions;
+
+namespace ICD.Common.Utils.Collections
+{
+	public sealed class WeakKeyReference<T> : WeakReference
+	{
+		private readonly int m_HashCode;
+
+		public new T Target { get { return (T)base.Target; } }
+
+		public int HashCode { get { return m_HashCode; } }
+
+		/// <summary>
+		/// Constructor.
+		/// </summary>
+		/// <param name="key"></param>
+		public WeakKeyReference(T key)
+			: this(key, EqualityComparer<T>.Default)
+		{
+		}
+
+		/// <summary>
+		/// Constructor.
+		/// </summary>
+		/// <param name="key"></param>
+		/// <param name="comparer"></param>
+		public WeakKeyReference(T key, IEqualityComparer<T> comparer)
+			: base(key)
+		{
+			if (comparer == null)
+				throw new ArgumentNullException("comparer");
+
+			// Retain the object's hash code immediately so that even
+			// if the target is GC'ed we will be able to find and
+			// remove the dead weak reference.
+			m_HashCode = comparer.GetHashCode(key);
+		}
+	}
+
+	public sealed class WeakKeyComparer<T> : IEqualityComparer<WeakKeyReference<T>>
+	{
+		private readonly IEqualityComparer<T> m_Comparer;
+
+		/// <summary>
+		/// Constructor.
+		/// </summary>
+		/// <param name="comparer"></param>
+		public WeakKeyComparer(IEqualityComparer<T> comparer)
+		{
+			if (comparer == null)
+				comparer = EqualityComparer<T>.Default;
+
+			m_Comparer = comparer;
+		}
+
+		public int GetHashCode(WeakKeyReference<T> weakKey)
+		{
+			return weakKey.HashCode;
+		}
+
+		// Note: There are actually 9 cases to handle here.
+		//
+		//  Let Wa = Alive Weak Reference
+		//  Let Wd = Dead Weak Reference
+		//  Let S  = Strong Reference
+		//  
+		//  x  | y  | Equals(x,y)
+		// -------------------------------------------------
+		//  Wa | Wa | comparer.Equals(x.Target, y.Target) 
+		//  Wa | Wd | false
+		//  Wa | S  | comparer.Equals(x.Target, y)
+		//  Wd | Wa | false
+		//  Wd | Wd | x == y
+		//  Wd | S  | false
+		//  S  | Wa | comparer.Equals(x, y.Target)
+		//  S  | Wd | false
+		//  S  | S  | comparer.Equals(x, y)
+		// -------------------------------------------------
+		public bool Equals(WeakKeyReference<T> x, WeakKeyReference<T> y)
+		{
+			bool xIsDead;
+			bool yIsDead;
+
+			T first = GetTarget(x, out xIsDead);
+			T second = GetTarget(y, out yIsDead);
+
+			if (xIsDead)
+				return yIsDead && x == y;
+
+			return !yIsDead && m_Comparer.Equals(first, second);
+		}
+
+		private static T GetTarget(WeakKeyReference<T> obj, out bool isDead)
+		{
+			T target = obj.Target;
+			isDead = !obj.IsAlive;
+			return target;
+		}
+	}
+
+
+	/// <summary>
+	/// WeakDictionary keeps weak references to keys and drops key/value pairs once the key is garbage collected.
+	/// </summary>
+	/// <typeparam name="TKey"></typeparam>
+	/// <typeparam name="TValue"></typeparam>
+	public sealed class WeakKeyDictionary<TKey, TValue> : IDictionary<TKey, TValue>
+	{
+		private readonly Dictionary<WeakKeyReference<TKey>, TValue> m_Dictionary;
+		private readonly IEqualityComparer<TKey> m_Comparer;
+
+		#region Properties
+
+		public int Count
+		{
+			get
+			{
+				RemoveCollectedEntries();
+				return m_Dictionary.Count;
+			}
+		}
+
+		public bool IsReadOnly { get { return false; } }
+
+		public ICollection<TKey> Keys { get { throw new NotImplementedException(); } }
+
+		public ICollection<TValue> Values { get { throw new NotImplementedException(); } }
+
+		public TValue this[TKey key]
+		{
+			get
+			{
+				TValue output;
+				if (TryGetValue(key, out output))
+					return output;
+
+				throw new KeyNotFoundException();
+			}
+			set
+			{
+				if (key == null)
+					throw new ArgumentNullException("key");
+
+				WeakKeyReference<TKey> weakKey = new WeakKeyReference<TKey>(key, m_Comparer);
+				m_Dictionary[weakKey] = value;
+			}
+		}
+
+		#endregion
+
+		public WeakKeyDictionary()
+			: this(0)
+		{
+		}
+
+		public WeakKeyDictionary(int capacity)
+			: this(capacity, EqualityComparer<TKey>.Default)
+		{
+		}
+
+		public WeakKeyDictionary(IEqualityComparer<TKey> comparer)
+			: this(0, comparer)
+		{
+		}
+
+		public WeakKeyDictionary(int capacity, IEqualityComparer<TKey> comparer)
+		{
+			m_Comparer = comparer;
+
+			WeakKeyComparer<TKey> keyComparer = new WeakKeyComparer<TKey>(m_Comparer);
+			m_Dictionary = new Dictionary<WeakKeyReference<TKey>, TValue>(capacity, keyComparer);
+		}
+
+		#region Methods
+
+		bool ICollection<KeyValuePair<TKey, TValue>>.Remove(KeyValuePair<TKey, TValue> item)
+		{
+			throw new NotImplementedException();
+		}
+
+		public void Add(TKey key, TValue value)
+		{
+			if (key == null)
+				throw new ArgumentNullException("key");
+
+			WeakKeyReference<TKey> weakKey = new WeakKeyReference<TKey>(key, m_Comparer);
+			IcdConsole.PrintLine("Adding key {0} with hash code {1}", weakKey.Target, weakKey.HashCode);
+
+			m_Dictionary.Add(weakKey, value);
+
+			IcdConsole.PrintLine("Internal dict count is now {0}", m_Dictionary.Count);
+		}
+
+		public bool ContainsKey(TKey key)
+		{
+			TValue unused;
+			return TryGetValue(key, out unused);
+		}
+
+		public bool Remove(TKey key)
+		{
+			return m_Dictionary.Remove(new WeakKeyReference<TKey>(key, m_Comparer));
+		}
+
+		public bool TryGetValue(TKey key, out TValue value)
+		{
+			return m_Dictionary.TryGetValue(new WeakKeyReference<TKey>(key, m_Comparer), out value);
+		}
+
+		public void Clear()
+		{
+			m_Dictionary.Clear();
+		}
+
+		/// <summary>
+		/// Removes the left-over weak references for entries in the dictionary
+		/// whose key or value has already been reclaimed by the garbage
+		/// collector. This will reduce the dictionary's Count by the number
+		/// of dead key-value pairs that were eliminated.
+		/// </summary>
+		[PublicAPI]
+		public void RemoveCollectedEntries()
+		{
+			IEnumerable<WeakKeyReference<TKey>> toRemove =
+				m_Dictionary.Select(pair => pair.Key)
+				            .Where(weakKey => !weakKey.IsAlive)
+							.ToArray();
+
+			IcdConsole.PrintLine("-------------------");
+			foreach (var item in toRemove)
+				IcdConsole.PrintLine("{0} - {1}", item, item.Target);
+			IcdConsole.PrintLine("-------------------");
+
+			m_Dictionary.RemoveAll(toRemove);
+		}
+
+		#region ICollection
+
+		void ICollection<KeyValuePair<TKey, TValue>>.Add(KeyValuePair<TKey, TValue> item)
+		{
+			Add(item.Key, item.Value);
+		}
+
+		bool ICollection<KeyValuePair<TKey, TValue>>.Contains(KeyValuePair<TKey, TValue> item)
+		{
+			throw new NotImplementedException();
+		}
+
+		void ICollection<KeyValuePair<TKey, TValue>>.CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
+		{
+			throw new NotImplementedException();
+		}
+
+		#endregion
+
+		#region IEnumerator
+
+		public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
+		{
+			foreach (KeyValuePair<WeakKeyReference<TKey>, TValue> kvp in m_Dictionary)
+			{
+				WeakKeyReference<TKey> weakKey = kvp.Key;
+				TKey key = weakKey.Target;
+				if (weakKey.IsAlive)
+					yield return new KeyValuePair<TKey, TValue>(key, kvp.Value);
+			}
+		}
+
+		IEnumerator IEnumerable.GetEnumerator()
+		{
+			return GetEnumerator();
+		}
+
+		#endregion
+
+		#endregion
+	}
+}