beagled/Lucene.Net/Search/CachingWrapperFilter.cs

   1 /*
   2  * Copyright 2004 The Apache Software Foundation
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  * http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 using System;
  17 using System.Runtime.InteropServices;
  18 using IndexReader = Lucene.Net.Index.IndexReader;
  19 namespace Lucene.Net.Search
  20 {
  21
  22         /// <summary> Wraps another filters result and caches it.  The caching
  23         /// behavior is like {@link QueryFilter}.  The purpose is to allow
  24         /// filters to simply filter, and then wrap with this class to add
  25         /// caching, keeping the two concerns decoupled yet composable.
  26         /// </summary>
  27         [Serializable]
  28         public class CachingWrapperFilter:Filter
  29         {
  30                 private Filter filter;
  31
  32                 /// <todo>  What about serialization in RemoteSearchable?  Caching won't work. </todo>
  33                 /// <summary>       Should transient be removed?
  34                 /// </summary>
  35                 [NonSerialized]
  36                 private System.Collections.IDictionary cache;
  37
  38                 /// <param name="filter">Filter to cache results of
  39                 /// </param>
  40                 public CachingWrapperFilter(Filter filter)
  41                 {
  42                         this.filter = filter;
  43                 }
  44
  45                 public override System.Collections.BitArray Bits(IndexReader reader)
  46                 {
  47                         if (cache == null)
  48                         {
  49                                 cache = new System.Collections.Hashtable();
  50                         }
  51
  52                         lock (cache.SyncRoot)
  53                         {
  54                                 // check cache
  55                                 System.Collections.BitArray cached = (System.Collections.BitArray) cache[reader];
  56                                 if (cached != null)
  57                                 {
  58                                         return cached;
  59                                 }
  60                         }
  61
  62                         System.Collections.BitArray bits = filter.Bits(reader);
  63
  64                         lock (cache.SyncRoot)
  65                         {
  66                                 // update cache
  67                                 cache[reader] = bits;
  68                         }
  69
  70                         return bits;
  71                 }
  72
  73                 public override System.String ToString()
  74                 {
  75                         return "CachingWrapperFilter(" + filter + ")";
  76                 }
  77         }
  78 }