Imported Upstream version 5.4.0.167

Former-commit-id: 5624ac747d633e885131e8349322922b6a59baaa

external/api-doc-tools/monodoc/Mono.Utilities/MemoryLRU.cs

@@ -0,0 +1,92 @@
+/* 
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+using System;
+using System.Collections.Generic;
+
+namespace Mono.Utilities
+{
+    public class LRUCache<TKey, TValue>
+    {
+	    [ThreadStatic]
+	    static LRUCache<TKey, TValue> deflt;
+
+	    public static LRUCache<TKey, TValue> Default {
+		    get {
+			    return deflt != null ? deflt : (deflt = new LRUCache<TKey, TValue> (5));
+		    }
+	    }
+
+        int capacity;
+        LinkedList<ListValueEntry<TKey, TValue>> list;
+        Dictionary<TKey, LinkedListNode<ListValueEntry<TKey, TValue>>> lookup;
+        LinkedListNode<ListValueEntry<TKey, TValue>> openNode;
+
+        public LRUCache (int capacity)
+        {
+            this.capacity = capacity;
+            this.list = new LinkedList<ListValueEntry<TKey, TValue>>();
+            this.lookup = new Dictionary<TKey, LinkedListNode<ListValueEntry<TKey, TValue>>> (capacity + 1);
+            this.openNode = new LinkedListNode<ListValueEntry<TKey, TValue>>(new ListValueEntry<TKey, TValue> (default(TKey), default(TValue)));
+        }
+
+        public void Put (TKey key, TValue value)
+        {
+            if (Get(key) == null) {
+                this.openNode.Value.Itemkey = key;
+                this.openNode.Value.Itemvalue = value;
+                this.list.AddFirst (this.openNode);
+                this.lookup.Add (key, this.openNode);
+
+                if (this.list.Count > this.capacity) {
+                    // last node is to be removed and saved for the next addition to the cache
+                    this.openNode = this.list.Last;
+
+                    // remove from list & dictionary
+                    this.list.RemoveLast();
+                    this.lookup.Remove(this.openNode.Value.Itemkey);
+                } else {
+                    // still filling the cache, create a new open node for the next time
+                    this.openNode = new LinkedListNode<ListValueEntry<Tkey, Tvalue>>(new ListValueEntry<Tkey, Tvalue>(default(Tkey), default(Tvalue)));
+                }
+            }
+        }
+
+        public TValue Get (TKey key)
+        {
+            LinkedListNode<ListValueEntry<TKey, TValue>> node = null;
+            if (!this.lookup.TryGetValue (key, out node))
+                return default (TValue);
+            this.list.Remove (node);
+            this.list.AddFirst (node);
+            return node.Value.ItemValue;
+        }
+
+        class ListValueEntry<K, V> where K : TKey 
+                                   where V : TValue
+        {
+            internal V ItemValue;
+            internal K ItemKey;
+
+            internal ListValueEntry(K key, V value)
+            {
+                this.ItemKey = key;
+                this.ItemValue = value;
+            }
+        }
+    }
+}