1 /*
2  * Copyright (C) 2010 Apple Inc. All rights reserved.
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
7  * 1. Redistributions of source code must retain the above copyright
8  *    notice, this list of conditions and the following disclaimer.
9  * 2. Redistributions in binary form must reproduce the above copyright
10  *    notice, this list of conditions and the following disclaimer in the
11  *    documentation and/or other materials provided with the distribution.
12  *
13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
14  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
15  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
17  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
18  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
19  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
20  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
21  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
22  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
23  * THE POSSIBILITY OF SUCH DAMAGE.
24  */
25 
26 #ifndef AtomicStringKeyedMRUCache_h
27 #define AtomicStringKeyedMRUCache_h
28 
29 #include <wtf/text/AtomicString.h>
30 
31 namespace WebCore {
32 
33 template<typename T, size_t capacity = 4>
34 class AtomicStringKeyedMRUCache {
35 public:
get(const AtomicString & key)36     T get(const AtomicString& key)
37     {
38         if (key.isNull()) {
39             DEFINE_STATIC_LOCAL(T, valueForNull, (createValueForNullKey()));
40             return valueForNull;
41         }
42 
43         for (size_t i = 0; i < m_cache.size(); ++i) {
44             if (m_cache[i].first == key) {
45                 size_t foundIndex = i;
46                 if (foundIndex + 1 < m_cache.size()) {
47                     Entry entry = m_cache[foundIndex];
48                     m_cache.remove(foundIndex);
49                     foundIndex = m_cache.size();
50                     m_cache.append(entry);
51                 }
52                 return m_cache[foundIndex].second;
53             }
54         }
55         if (m_cache.size() == capacity)
56             m_cache.remove(0);
57 
58         m_cache.append(std::make_pair(key, createValueForKey(key)));
59         return m_cache.last().second;
60     }
61 
62 private:
63     T createValueForNullKey();
64     T createValueForKey(const AtomicString&);
65 
66     typedef pair<AtomicString, T> Entry;
67     typedef Vector<Entry, capacity> Cache;
68     Cache m_cache;
69 };
70 
71 }
72 
73 #endif // AtomicStringKeyedMRUCache_h
74