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1   package org.apache.commons.jcs.engine.memory.lru;
2   
3   /*
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *   http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing,
15   * software distributed under the License is distributed on an
16   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17   * KIND, either express or implied.  See the License for the
18   * specific language governing permissions and limitations
19   * under the License.
20   */
21  
22  import java.io.IOException;
23  
24  import org.apache.commons.jcs.engine.behavior.ICacheElement;
25  import org.apache.commons.jcs.engine.memory.AbstractDoubleLinkedListMemoryCache;
26  import org.apache.commons.jcs.engine.memory.util.MemoryElementDescriptor;
27  
28  /**
29   * A fast reference management system. The least recently used items move to the end of the list and
30   * get spooled to disk if the cache hub is configured to use a disk cache. Most of the cache
31   * bottlenecks are in IO. There are no io bottlenecks here, it's all about processing power.
32   * <p>
33   * Even though there are only a few adjustments necessary to maintain the double linked list, we
34   * might want to find a more efficient memory manager for large cache regions.
35   * <p>
36   * The LRUMemoryCache is most efficient when the first element is selected. The smaller the region,
37   * the better the chance that this will be the case. &lt; .04 ms per put, p3 866, 1/10 of that per get
38   */
39  public class LRUMemoryCache<K, V>
40      extends AbstractDoubleLinkedListMemoryCache<K, V>
41  {
42      /**
43       * Puts an item to the cache. Removes any pre-existing entries of the same key from the linked
44       * list and adds this one first.
45       * <p>
46       * @param ce The cache element, or entry wrapper
47       * @return MemoryElementDescriptor the new node
48       * @throws IOException
49       */
50      @Override
51      protected MemoryElementDescriptor<K, V> adjustListForUpdate( ICacheElement<K, V> ce )
52          throws IOException
53      {
54          return addFirst( ce );
55      }
56  
57      /**
58       * Makes the item the first in the list.
59       * <p>
60       * @param me
61       */
62      @Override
63      protected void adjustListForGet( MemoryElementDescriptor<K, V> me )
64      {
65          list.makeFirst( me );
66      }
67  }