apewer-dotnet/Apewer.Source/Externals/MySql.Data-6.10.9/MySqlClient/TableCache.cs

#if MYSQL_6_10

// Copyright ?2016, 2018, Oracle and/or its affiliates. All rights reserved.
//
// MySQL Connector/NET is licensed under the terms of the GPLv2
// <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most 
// MySQL Connectors. There are special exceptions to the terms and 
// conditions of the GPLv2 as it is applied to this software, see the 
// FLOSS License Exception
// <http://www.mysql.com/about/legal/licensing/foss-exception.html>.
//
// This program is free software; you can redistribute it and/or modify 
// it under the terms of the GNU General Public License as published 
// by the Free Software Foundation; version 2 of the License.
//
// This program is distributed in the hope that it will be useful, but 
// WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 
// for more details.
//
// You should have received a copy of the GNU General Public License along 
// with this program; if not, write to the Free Software Foundation, Inc., 
// 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA

using System;
using System.Collections.Generic;
using System.Linq;

namespace Externals.MySql.Data.MySqlClient
{
    internal class TableCache
    {
        private static readonly BaseTableCache cache;

        static TableCache()
        {
            cache = new BaseTableCache(480 /* 8 hour max by default */);
        }

        public static void AddToCache(string commandText, ResultSet resultSet)
        {
            cache.AddToCache(commandText, resultSet);
        }

        public static ResultSet RetrieveFromCache(string commandText, int cacheAge)
        {
            return (ResultSet)cache.RetrieveFromCache(commandText, cacheAge);
        }

        public static void RemoveFromCache(string commandText)
        {
            cache.RemoveFromCache(commandText);
        }

        public static void DumpCache()
        {
            cache.Dump();
        }
    }

    /// <summary>
    /// Defines the basic operations to be performed on the table cache.
    /// </summary>
    internal class BaseTableCache
    {
        /// <summary>
        /// The maximum age allowed for cache entries.
        /// </summary>
        protected int MaxCacheAge;

        private Dictionary<string, CacheEntry> cache = new Dictionary<string, CacheEntry>();

        public BaseTableCache(int maxCacheAge)
        {
            MaxCacheAge = maxCacheAge;
        }

        /// <summary>
        /// Adds the given command and result set to the cache.
        /// </summary>
        /// <param name="commandText">The command to store in the cache.</param>
        /// <param name="resultSet">The resultset associated to the stored command.</param>
        public virtual void AddToCache(string commandText, object resultSet)
        {
            CleanCache();
            CacheEntry entry = new CacheEntry();
            entry.CacheTime = DateTime.Now;
            entry.CacheElement = resultSet;
            lock (cache)
            {
                if (cache.ContainsKey(commandText)) return;
                cache.Add(commandText, entry);
            }
        }

        /// <summary>
        /// Retrieves the specified command from the cache.
        /// </summary>
        /// <param name="commandText">The command to retrieve.</param>
        /// <param name="cacheAge">The allowed age for the cache entry.</param>
        /// <returns></returns>
        public virtual object RetrieveFromCache(string commandText, int cacheAge)
        {
            CleanCache();
            lock (cache)
            {
                if (!cache.ContainsKey(commandText)) return null;
                CacheEntry entry = cache[commandText];
                if (DateTime.Now.Subtract(entry.CacheTime).TotalSeconds > cacheAge) return null;
                return entry.CacheElement;
            }
        }

        /// <summary>
        /// Removes the specified command from the cache.
        /// </summary>
        /// <param name="commandText">The command to remove from the cache.</param>
        public void RemoveFromCache(string commandText)
        {
            lock (cache)
            {
                if (!cache.ContainsKey(commandText)) return;
                cache.Remove(commandText);
            }
        }

        /// <summary>
        /// Clears the cache.
        /// </summary>
        public virtual void Dump()
        {
            lock (cache)
                cache.Clear();
        }

        /// <summary>
        /// Removes cache entries older than the value defined by <see cref="MaxCacheAge"/>.
        /// </summary>
        protected virtual void CleanCache()
        {
            DateTime now = DateTime.Now;
            List<string> keysToRemove = new List<string>();

            lock (cache)
            {
                keysToRemove.AddRange(from key in cache.Keys let diff = now.Subtract(cache[key].CacheTime) where diff.TotalSeconds > MaxCacheAge select key);

                foreach (string key in keysToRemove)
                    cache.Remove(key);
            }
        }

        private struct CacheEntry
        {
            public DateTime CacheTime;
            public object CacheElement;
        }
    }

}

#endif