MemoryCache.cs

Go to the documentation of this file.

// 
//  Copyright 2010-2015 Deveel
// 
//    Licensed 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 Deveel.Data.Caching {
    public class MemoryCache : Cache {
        protected LinkedList<KeyValuePair<object, CacheValue>> IndexList { get; private set; }

        private readonly Dictionary<object, CacheValue> valueCache = new Dictionary<object, CacheValue>();

        private readonly object syncRoot = new object();
        private DateTime lastCacheAccess = DateTime.MaxValue;

        public MemoryCache() {
            IndexList = new LinkedList<KeyValuePair<object, CacheValue>>();
        }

        // Some statistics about the hashing algorithm.
        private long totalGets = 0;
        private long getTotal = 0;

        protected virtual void UpdateElementAccess(object key, CacheValue cacheValue) {
            // update last access and move it to the head of the list
            cacheValue.LastAccess = DateTime.Now;
            var idxRef = cacheValue.IndexRef;
            if (idxRef != null) {
                IndexList.Remove(idxRef);
            } else {
                idxRef = new LinkedListNode<KeyValuePair<object, CacheValue>>(new KeyValuePair<object, CacheValue>(key, cacheValue));
                cacheValue.IndexRef = idxRef;
            }

            IndexList.AddFirst(idxRef);
        }

        protected virtual CacheValue GetCacheValueUnlocked(object key) {
            CacheValue v;
            return valueCache.TryGetValue(key, out v) ? v : null;
        }

        protected virtual CacheValue SetValueUnlocked(object key, object value) {
            lastCacheAccess = DateTime.Now;
            var cacheValue = GetCacheValueUnlocked(key);

            if (cacheValue == null) {
                cacheValue = new CacheValue(value);
                cacheValue.IsNew = true;
                valueCache[key] = cacheValue;
            } else {
                cacheValue.Value = value;
                cacheValue.IsNew = false;
            }

            UpdateElementAccess(key, cacheValue);
            return cacheValue;
        }

        protected object RemoveUnlocked(object key) {
            var value = GetCacheValueUnlocked(key);
            if (value != null) {
                valueCache.Remove(key);
                IndexList.Remove(value.IndexRef);
                return value.Value;
            }

            return null;
        }

        protected override bool SetObject(object key, object value) {
            lock (syncRoot) {
                var cached = SetValueUnlocked(key, value);
                return cached.IsNew;
            }
        }

        protected override bool TryGetObject(object key, out object value) {
            CacheValue v;
            value = null;

            lock (syncRoot) {
                lastCacheAccess = DateTime.Now;
                v = GetCacheValueUnlocked(key);
                if (v != null) {
                    value = v.Value;
                    UpdateElementAccess(key, v);
                    return true;
                }
            }

            return false;
        }

        protected override object RemoveObject(object key) {
            lock (syncRoot) {
                lastCacheAccess = DateTime.Now;

                return RemoveUnlocked(key);
            }
        }

        public override void Clear() {
            lock (syncRoot) {
                valueCache.Clear();
                IndexList.Clear();
            }

            base.Clear();
        }

        protected override void Dispose(bool disposing) {
            if (disposing) {
                Clear();
            }


            base.Dispose(disposing);
        }

        #region CachedValue

        protected sealed class CacheValue {
            public CacheValue(object value) {
                LastAccess = DateTime.Now;
                Value = value;
            }

            public LinkedListNode<KeyValuePair<object, CacheValue>> IndexRef { get; set; }

            public DateTime LastAccess { get; set; }

            public object Value { get; set; }

            public bool IsNew { get; set; }
        }

        #endregion
    }
}