class/Npgsql/Npgsql/Cache.cs

   1 // created on 29/11/2007
   2
   3 // Npgsql.NpgsqlConnectionStringBuilder.cs
   4 //
   5 // Author:
   6 //      Glen Parker (glenebob@nwlink.com)
   7 //      Ben Sagal (bensagal@gmail.com)
   8 //      Tao Wang (dancefire@gmail.com)
   9 //
  10 //      Copyright (C) 2007 The Npgsql Development Team
  11 //      npgsql-general@gborg.postgresql.org
  12 //      http://gborg.postgresql.org/project/npgsql/projdisplay.php
  13 //
  14 // Permission to use, copy, modify, and distribute this software and its
  15 // documentation for any purpose, without fee, and without a written
  16 // agreement is hereby granted, provided that the above copyright notice
  17 // and this paragraph and the following two paragraphs appear in all copies.
  18 //
  19 // IN NO EVENT SHALL THE NPGSQL DEVELOPMENT TEAM BE LIABLE TO ANY PARTY
  20 // FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
  21 // INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
  22 // DOCUMENTATION, EVEN IF THE NPGSQL DEVELOPMENT TEAM HAS BEEN ADVISED OF
  23 // THE POSSIBILITY OF SUCH DAMAGE.
  24 //
  25 // THE NPGSQL DEVELOPMENT TEAM SPECIFICALLY DISCLAIMS ANY WARRANTIES,
  26 // INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
  27 // AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
  28 // ON AN "AS IS" BASIS, AND THE NPGSQL DEVELOPMENT TEAM HAS NO OBLIGATIONS
  29 // TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
  30
  31 using System;
  32 using System.Collections.Generic;
  33 //using System.Text;
  34
  35 namespace Npgsql
  36 {
  37         internal class Cache<TEntity> : LinkedList<KeyValuePair<string, TEntity>>
  38                 where TEntity : class
  39         {
  40                 private int _cache_size = 20;
  41
  42                 /// <summary>
  43                 /// Set Cache Size. The default value is 20.
  44                 /// </summary>
  45                 public int CacheSize
  46                 {
  47                         get { return _cache_size; }
  48                         set
  49                         {
  50                                 if (value < 0) { throw new ArgumentOutOfRangeException("CacheSize"); }
  51
  52                                 _cache_size = value;
  53
  54                                 if (this.Count > _cache_size)
  55                                 {
  56                                         lock (this)
  57                                         {
  58                                                 while (_cache_size < this.Count)
  59                                                 {
  60                                                         RemoveLast();
  61                                                 }
  62                                         }
  63                                 }
  64                         }
  65                 }
  66
  67                 /// <summary>
  68                 /// Lookup cached entity. null will returned if not match.
  69                 /// For both get{} and set{} apply LRU rule.
  70                 /// </summary>
  71                 /// <param name="key">key</param>
  72                 /// <returns></returns>
  73                 public TEntity this[string key]
  74                 {
  75                         get
  76                         {
  77                                 lock (this)
  78                                 {
  79                                         for (LinkedListNode<KeyValuePair<string, TEntity>> node = this.First; node != null; node = node.Next)
  80                                         {
  81                                                 if (node.Value.Key == key)
  82                                                 {
  83                                                         this.Remove(node);
  84                                                         this.AddFirst(node);
  85                                                         return node.Value.Value;
  86                                                 }
  87                                         }
  88                                 }
  89                                 return null;
  90                         }
  91                         set
  92                         {
  93                                 lock (this)
  94                                 {
  95                                         for (LinkedListNode<KeyValuePair<string, TEntity>> node = this.First; node != null; node = node.Next)
  96                                         {
  97                                                 if (node.Value.Key == key)
  98                                                 {
  99                                                         this.Remove(node);
 100                                                         this.AddFirst(node);
 101                                                         return;
 102                                                 }
 103                                         }
 104                                         if (this.CacheSize > 0)
 105                                         {
 106                                                 this.AddFirst(new KeyValuePair<string, TEntity>(key, value));
 107                                                 if (this.Count > this.CacheSize)
 108                                                 {
 109                                                         this.RemoveLast();
 110                                                 }
 111                                         }
 112                                 }
 113                         }
 114                 }
 115
 116                 public Cache() : base() { }
 117                 public Cache(int cacheSize) : base()
 118                 {
 119                         this._cache_size = cacheSize;
 120                 }
 121         }
 122 }