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      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:
     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