Initial commit - WPinternals 2.6

DiscUtils/ObjectCache.cs

@@ -0,0 +1,150 @@
+//
+// Copyright (c) 2008-2011, Kenneth Bell
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+//
+
+namespace DiscUtils
+{
+    using System;
+    using System.Collections;
+    using System.Collections.Generic;
+
+    /// <summary>
+    /// Caches objects.
+    /// </summary>
+    /// <typeparam name="K">The type of the object key.</typeparam>
+    /// <typeparam name="V">The type of the objects to cache.</typeparam>
+    /// <remarks>
+    /// Can be use for two purposes - to ensure there is only one instance of a given object,
+    /// and to prevent the need to recreate objects that are expensive to create.
+    /// </remarks>
+    internal class ObjectCache<K, V>
+    {
+        private const int MostRecentListSize = 20;
+        private const int PruneGap = 500;
+
+        private Dictionary<K, WeakReference> _entries;
+        private List<KeyValuePair<K, V>> _recent;
+        private int _nextPruneCount;
+
+        public ObjectCache()
+        {
+            _entries = new Dictionary<K, WeakReference>();
+            _recent = new List<KeyValuePair<K, V>>();
+        }
+
+        public V this[K key]
+        {
+            get
+            {
+                for (int i = 0; i < _recent.Count; ++i)
+                {
+                    KeyValuePair<K, V> recentEntry = _recent[i];
+                    if (recentEntry.Key.Equals(key))
+                    {
+                        MakeMostRecent(i);
+                        return recentEntry.Value;
+                    }
+                }
+
+                WeakReference wRef;
+                if (_entries.TryGetValue(key, out wRef))
+                {
+                    V val = (V)wRef.Target;
+                    if (val != null)
+                    {
+                        MakeMostRecent(key, val);
+                    }
+
+                    return val;
+                }
+
+                return default(V);
+            }
+
+            set
+            {
+                _entries[key] = new WeakReference(value);
+                MakeMostRecent(key, value);
+                PruneEntries();
+            }
+        }
+
+        internal void Remove(K key)
+        {
+            for (int i = 0; i < _recent.Count; ++i)
+            {
+                if (_recent[i].Key.Equals(key))
+                {
+                    _recent.RemoveAt(i);
+                    break;
+                }
+            }
+
+            _entries.Remove(key);
+        }
+
+        private void PruneEntries()
+        {
+            _nextPruneCount++;
+
+            if (_nextPruneCount > PruneGap)
+            {
+                List<K> toPrune = new List<K>();
+                foreach (var entry in _entries)
+                {
+                    if (!entry.Value.IsAlive)
+                    {
+                        toPrune.Add(entry.Key);
+                    }
+                }
+
+                foreach (var key in toPrune)
+                {
+                    _entries.Remove(key);
+                }
+
+                _nextPruneCount = 0;
+            }
+        }
+
+        private void MakeMostRecent(int i)
+        {
+            if (i == 0)
+            {
+                return;
+            }
+
+            KeyValuePair<K, V> entry = _recent[i];
+            _recent.RemoveAt(i);
+            _recent.Insert(0, entry);
+        }
+
+        private void MakeMostRecent(K key, V val)
+        {
+            while (_recent.Count >= MostRecentListSize)
+            {
+                _recent.RemoveAt(_recent.Count - 1);
+            }
+
+            _recent.Insert(0, new KeyValuePair<K, V>(key, val));
+        }
+    }
+}