1 /* 2 * File: lrucache.hpp 3 * Author: Alexander Ponomarev 4 * 5 * Created on June 20, 2013, 5:09 PM 6 */ 7 8 /* 9 * Redistribution and use in source and binary forms, with or without 10 modification, are permitted provided that the following conditions are met: 11 12 * Redistributions of source code must retain the above copyright notice, this 13 list of conditions and the following disclaimer. 14 15 * Redistributions in binary form must reproduce the above copyright notice, 16 this list of conditions and the following disclaimer in the documentation 17 and/or other materials provided with the distribution. 18 19 * Neither the name of lamerman nor the names of its 20 contributors may be used to endorse or promote products derived from 21 this software without specific prior written permission. 22 23 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 24 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 26 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE 27 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 29 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 30 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 31 OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 32 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 33 */ 34 35 #ifndef _LRUCACHE_HPP_INCLUDED_ 36 #define _LRUCACHE_HPP_INCLUDED_ 37 38 #include <unordered_map> 39 #include <list> 40 #include <cstddef> 41 #include <stdexcept> 42 43 namespace cache { 44 45 template<typename key_t, typename value_t> 46 class lru_cache { 47 public: 48 typedef typename std::pair<key_t, value_t> key_value_pair_t; 49 typedef typename std::list<key_value_pair_t>::iterator list_iterator_t; 50 lru_cache(size_t max_size)51 lru_cache(size_t max_size) : 52 _max_size(max_size) { 53 } 54 remove_last()55 value_t remove_last() { 56 auto last = _cache_items_list.end(); 57 last--; 58 auto t = last->second; 59 _cache_items_map.erase(last->first); 60 _cache_items_list.pop_back(); 61 62 return t; 63 } 64 put(const key_t & key,const value_t & value)65 value_t put(const key_t& key, const value_t& value) { 66 auto it = _cache_items_map.find(key); 67 _cache_items_list.push_front(key_value_pair_t(key, value)); 68 if (it != _cache_items_map.end()) { 69 _cache_items_list.erase(it->second); 70 _cache_items_map.erase(it); 71 } 72 _cache_items_map[key] = _cache_items_list.begin(); 73 74 if (_cache_items_map.size() > _max_size) { 75 auto t = remove_last(); 76 return t; 77 } else { 78 //throw std::range_error("no cache dropped from put"); 79 return nullptr; 80 } 81 } 82 83 //just retrieve value without updating position in the lru list __get(const key_t & key)84 value_t __get(const key_t& key) { 85 auto it = _cache_items_map.find(key); 86 if (it == _cache_items_map.end()) 87 return nullptr; 88 else 89 return it->second->second; 90 } 91 get(const key_t & key)92 value_t get(const key_t& key) { 93 auto it = _cache_items_map.find(key); 94 if (it == _cache_items_map.end()) { 95 //throw std::range_error("There is no such key in cache"); 96 return nullptr; 97 } else { 98 _cache_items_list.splice(_cache_items_list.begin(), _cache_items_list, it->second); 99 return it->second->second; 100 } 101 } 102 exists(const key_t & key) const103 bool exists(const key_t& key) const { 104 return _cache_items_map.find(key) != _cache_items_map.end(); 105 } 106 size() const107 size_t size() const { 108 return _cache_items_map.size(); 109 } 110 get_lru_list_ro() const111 const std::list<key_value_pair_t>& get_lru_list_ro() const { 112 return _cache_items_list; 113 } 114 115 private: 116 std::list<key_value_pair_t> _cache_items_list; 117 std::unordered_map<key_t, list_iterator_t> _cache_items_map; 118 size_t _max_size; 119 }; 120 121 } // namespace cache 122 123 #endif /* _LRUCACHE_HPP_INCLUDED_ */ 124 125