/Merlin/Main/Runtime/Microsoft.Dynamic/Utils/CacheDict.cs

  1/* ****************************************************************************
  2 *
  3 * Copyright (c) Microsoft Corporation. 
  4 *
  5 * This source code is subject to terms and conditions of the Microsoft Public License. A 
  6 * copy of the license can be found in the License.html file at the root of this distribution. If 
  7 * you cannot locate the  Microsoft Public License, please send an email to 
  8 * dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound 
  9 * by the terms of the Microsoft Public License.
 10 *
 11 * You must not remove this notice, or any other, from this software.
 12 *
 13 *
 14 * ***************************************************************************/
 15
 16using System;
 17using System.Collections.Generic;
 18using System.Text;
 19using System.Diagnostics;
 20
 21namespace Microsoft.Scripting.Utils {
 22    /// <summary>
 23    /// Provides a dictionary-like object used for caches which holds onto a maximum
 24    /// number of elements specified at construction time.
 25    /// 
 26    /// This class is not thread safe.
 27    /// </summary>
 28    public class CacheDict<TKey, TValue> {
 29        private readonly Dictionary<TKey, KeyInfo> _dict = new Dictionary<TKey, KeyInfo>();
 30        private readonly LinkedList<TKey> _list = new LinkedList<TKey>();
 31        private readonly int _maxSize;
 32
 33        /// <summary>
 34        /// Creates a dictionary-like object used for caches.
 35        /// </summary>
 36        /// <param name="maxSize">The maximum number of elements to store.</param>
 37        public CacheDict(int maxSize) {
 38            _maxSize = maxSize;
 39        }
 40
 41        /// <summary>
 42        /// Tries to get the value associated with 'key', returning true if it's found and
 43        /// false if it's not present.
 44        /// </summary>
 45        public bool TryGetValue(TKey key, out TValue value) {
 46            KeyInfo storedValue;
 47            if (_dict.TryGetValue(key, out storedValue)) {
 48                LinkedListNode<TKey> node = storedValue.List;
 49                if (node.Previous != null) {
 50                    // move us to the head of the list...
 51                    _list.Remove(node);
 52                    _list.AddFirst(node);
 53                }
 54
 55                value = storedValue.Value;
 56                return true;
 57            }
 58
 59            value = default(TValue);
 60            return false;
 61        }
 62
 63        /// <summary>
 64        /// Adds a new element to the cache, replacing and moving it to the front if the
 65        /// element is already present.
 66        /// </summary>
 67        public void Add(TKey key, TValue value) {
 68            KeyInfo keyInfo;
 69            if (_dict.TryGetValue(key, out keyInfo)) {
 70                // remove original entry from the linked list
 71                _list.Remove(keyInfo.List);
 72            } else if (_list.Count == _maxSize) {
 73                // we've reached capacity, remove the last used element...
 74                LinkedListNode<TKey> node = _list.Last;
 75                _list.RemoveLast();
 76                bool res = _dict.Remove(node.Value);
 77                Debug.Assert(res);
 78            }
 79            
 80            // add the new entry to the head of the list and into the dictionary
 81            LinkedListNode<TKey> listNode = new LinkedListNode<TKey>(key);
 82            _list.AddFirst(listNode);
 83            _dict[key] = new CacheDict<TKey, TValue>.KeyInfo(value, listNode);
 84        }
 85
 86        /// <summary>
 87        /// Returns the value associated with the given key, or throws KeyNotFoundException
 88        /// if the key is not present.
 89        /// </summary>
 90        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1065:DoNotRaiseExceptionsInUnexpectedLocations")]
 91        public TValue this[TKey key] {
 92            get {
 93                TValue res;
 94                if (TryGetValue(key, out res)) {
 95                    return res;
 96                }
 97                throw new KeyNotFoundException();
 98            }
 99            set {
100                Add(key, value);
101            }
102        }
103
104        private struct KeyInfo {
105            internal readonly TValue Value;
106            internal readonly LinkedListNode<TKey> List;
107
108            internal KeyInfo(TValue value, LinkedListNode<TKey> list) {
109                Value = value;
110                List = list;
111            }
112        }
113    }
114}