Mercurial > hg > orthanc
annotate Core/Cache/LeastRecentlyUsedIndex.h @ 507:c4122c3a47c1
access to oldest item in LRUCache
author | Sebastien Jodogne <s.jodogne@gmail.com> |
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date | Fri, 16 Aug 2013 10:24:49 +0200 |
parents | f59e4518fd57 |
children | e7841864c97c |
rev | line source |
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282 | 1 /** |
2 * Orthanc - A Lightweight, RESTful DICOM Store | |
398 | 3 * Copyright (C) 2012-2013 Medical Physics Department, CHU of Liege, |
282 | 4 * Belgium |
5 * | |
6 * This program is free software: you can redistribute it and/or | |
7 * modify it under the terms of the GNU General Public License as | |
8 * published by the Free Software Foundation, either version 3 of the | |
9 * License, or (at your option) any later version. | |
10 * | |
11 * In addition, as a special exception, the copyright holders of this | |
12 * program give permission to link the code of its release with the | |
13 * OpenSSL project's "OpenSSL" library (or with modified versions of it | |
14 * that use the same license as the "OpenSSL" library), and distribute | |
15 * the linked executables. You must obey the GNU General Public License | |
16 * in all respects for all of the code used other than "OpenSSL". If you | |
17 * modify file(s) with this exception, you may extend this exception to | |
18 * your version of the file(s), but you are not obligated to do so. If | |
19 * you do not wish to do so, delete this exception statement from your | |
20 * version. If you delete this exception statement from all source files | |
21 * in the program, then also delete it here. | |
22 * | |
23 * This program is distributed in the hope that it will be useful, but | |
24 * WITHOUT ANY WARRANTY; without even the implied warranty of | |
25 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
26 * General Public License for more details. | |
27 * | |
28 * You should have received a copy of the GNU General Public License | |
29 * along with this program. If not, see <http://www.gnu.org/licenses/>. | |
30 **/ | |
31 | |
32 | |
33 #pragma once | |
34 | |
35 #include <list> | |
36 #include <map> | |
37 #include <boost/noncopyable.hpp> | |
283 | 38 #include <cassert> |
39 | |
40 #include "../OrthancException.h" | |
284
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41 #include "../Toolbox.h" |
282 | 42 |
43 namespace Orthanc | |
44 { | |
45 /** | |
46 * This class implements the index of a cache with least recently | |
47 * used (LRU) recycling policy. All the items of the cache index | |
48 * can be associated with a payload. | |
49 * Reference: http://stackoverflow.com/a/2504317 | |
50 **/ | |
51 template <typename T, typename Payload = NullType> | |
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52 class LeastRecentlyUsedIndex : public boost::noncopyable |
282 | 53 { |
54 private: | |
55 typedef std::list< std::pair<T, Payload> > Queue; | |
56 typedef std::map<T, typename Queue::iterator> Index; | |
57 | |
58 Index index_; | |
59 Queue queue_; | |
60 | |
61 /** | |
62 * Internal method for debug builds to check whether the internal | |
63 * data structures are not corrupted. | |
64 **/ | |
65 void CheckInvariants() const; | |
66 | |
67 public: | |
68 /** | |
69 * Add a new element to the cache index, and make it the most | |
70 * recent element. | |
71 * \param id The ID of the element. | |
72 * \param payload The payload of the element. | |
73 **/ | |
74 void Add(T id, Payload payload = Payload()); | |
75 | |
76 /** | |
77 * When accessing an element of the cache, this method tags the | |
78 * element as the most recently used. | |
79 * \param id The most recently accessed item. | |
80 **/ | |
81 void TagAsMostRecent(T id); | |
82 | |
83 /** | |
84 * Remove an element from the cache index. | |
85 * \param id The item to remove. | |
86 **/ | |
87 Payload Invalidate(T id); | |
88 | |
89 /** | |
90 * Get the oldest element in the cache and remove it. | |
91 * \return The oldest item. | |
92 **/ | |
93 T RemoveOldest() | |
94 { | |
95 Payload p; | |
96 return RemoveOldest(p); | |
97 } | |
98 | |
99 /** | |
100 * Get the oldest element in the cache, remove it and return the | |
101 * associated payload. | |
102 * \param payload Where to store the associated payload. | |
103 * \return The oldest item. | |
104 **/ | |
105 T RemoveOldest(Payload& payload); | |
106 | |
107 /** | |
108 * Check whether an element is contained in the cache. | |
109 * \param id The item. | |
110 * \return \c true iff the item is indexed by the cache. | |
111 **/ | |
112 bool Contains(T id) const | |
113 { | |
114 return index_.find(id) != index_.end(); | |
115 } | |
116 | |
283 | 117 bool Contains(T id, Payload& payload) const |
118 { | |
119 typename Index::const_iterator it = index_.find(id); | |
120 if (it == index_.end()) | |
121 { | |
122 return false; | |
123 } | |
124 else | |
125 { | |
126 payload = it->second->second; | |
127 return true; | |
128 } | |
129 } | |
130 | |
131 /** | |
132 * Return the number of elements in the cache. | |
133 * \return The number of elements. | |
134 **/ | |
135 size_t GetSize() const | |
136 { | |
137 assert(index_.size() == queue_.size()); | |
138 return queue_.size(); | |
139 } | |
140 | |
282 | 141 /** |
142 * Check whether the cache index is empty. | |
143 * \return \c true iff the cache is empty. | |
144 **/ | |
145 bool IsEmpty() const | |
146 { | |
147 return index_.empty(); | |
148 } | |
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149 |
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150 const T& GetOldest() const; |
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151 |
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152 const Payload& GetOldestPayload() const; |
282 | 153 }; |
283 | 154 |
155 | |
156 | |
157 | |
158 /****************************************************************** | |
159 ** Implementation of the template | |
160 ******************************************************************/ | |
161 | |
162 template <typename T, typename Payload> | |
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163 void LeastRecentlyUsedIndex<T, Payload>::CheckInvariants() const |
283 | 164 { |
165 #ifndef NDEBUG | |
166 assert(index_.size() == queue_.size()); | |
167 | |
168 for (typename Index::const_iterator | |
169 it = index_.begin(); it != index_.end(); it++) | |
170 { | |
171 assert(it->second != queue_.end()); | |
172 assert(it->second->first == it->first); | |
173 } | |
174 #endif | |
175 } | |
176 | |
177 | |
178 template <typename T, typename Payload> | |
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179 void LeastRecentlyUsedIndex<T, Payload>::Add(T id, Payload payload) |
283 | 180 { |
181 if (Contains(id)) | |
182 { | |
183 throw OrthancException(ErrorCode_BadSequenceOfCalls); | |
184 } | |
185 | |
186 queue_.push_front(std::make_pair(id, payload)); | |
187 index_[id] = queue_.begin(); | |
188 | |
189 CheckInvariants(); | |
190 } | |
191 | |
192 | |
193 template <typename T, typename Payload> | |
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194 void LeastRecentlyUsedIndex<T, Payload>::TagAsMostRecent(T id) |
283 | 195 { |
196 if (!Contains(id)) | |
197 { | |
198 throw OrthancException(ErrorCode_InexistentItem); | |
199 } | |
200 | |
201 typename Index::iterator it = index_.find(id); | |
202 assert(it != index_.end()); | |
203 | |
204 std::pair<T, Payload> item = *(it->second); | |
205 | |
206 queue_.erase(it->second); | |
207 queue_.push_front(item); | |
208 index_[id] = queue_.begin(); | |
209 | |
210 CheckInvariants(); | |
211 } | |
212 | |
213 | |
214 template <typename T, typename Payload> | |
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215 Payload LeastRecentlyUsedIndex<T, Payload>::Invalidate(T id) |
283 | 216 { |
217 if (!Contains(id)) | |
218 { | |
219 throw OrthancException(ErrorCode_InexistentItem); | |
220 } | |
221 | |
222 typename Index::iterator it = index_.find(id); | |
223 assert(it != index_.end()); | |
224 | |
225 Payload payload = it->second->second; | |
226 queue_.erase(it->second); | |
227 index_.erase(it); | |
228 | |
229 CheckInvariants(); | |
230 return payload; | |
231 } | |
232 | |
233 | |
234 template <typename T, typename Payload> | |
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235 T LeastRecentlyUsedIndex<T, Payload>::RemoveOldest(Payload& payload) |
283 | 236 { |
237 if (IsEmpty()) | |
238 { | |
239 throw OrthancException(ErrorCode_BadSequenceOfCalls); | |
240 } | |
241 | |
242 std::pair<T, Payload> item = queue_.back(); | |
243 T oldest = item.first; | |
244 payload = item.second; | |
245 | |
246 queue_.pop_back(); | |
247 assert(index_.find(oldest) != index_.end()); | |
248 index_.erase(oldest); | |
249 | |
250 CheckInvariants(); | |
251 | |
252 return oldest; | |
253 } | |
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254 |
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255 |
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256 template <typename T, typename Payload> |
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257 const T& LeastRecentlyUsedIndex<T, Payload>::GetOldest() const |
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258 { |
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259 if (IsEmpty()) |
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260 { |
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261 throw OrthancException(ErrorCode_BadSequenceOfCalls); |
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262 } |
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263 |
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264 return queue_.back().first; |
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265 } |
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266 |
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267 |
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268 template <typename T, typename Payload> |
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269 const Payload& LeastRecentlyUsedIndex<T, Payload>::GetOldestPayload() const |
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270 { |
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271 if (IsEmpty()) |
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272 { |
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273 throw OrthancException(ErrorCode_BadSequenceOfCalls); |
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274 } |
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275 |
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276 return queue_.back().second; |
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277 } |
282 | 278 } |