Mercurial > hg > orthanc
comparison Core/MultiThreading/CacheIndex.h @ 282:915ed24547ea
cache lru policy
author | Sebastien Jodogne <s.jodogne@gmail.com> |
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date | Wed, 12 Dec 2012 13:17:42 +0100 |
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children | c9977db00e1d |
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1 /** | |
2 * Orthanc - A Lightweight, RESTful DICOM Store | |
3 * Copyright (C) 2012 Medical Physics Department, CHU of Liege, | |
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> | |
38 | |
39 namespace Orthanc | |
40 { | |
41 class NullType | |
42 { | |
43 }; | |
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> | |
52 class CacheIndex : public boost::noncopyable | |
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 | |
117 /** | |
118 * Check whether the cache index is empty. | |
119 * \return \c true iff the cache is empty. | |
120 **/ | |
121 bool IsEmpty() const | |
122 { | |
123 return index_.empty(); | |
124 } | |
125 }; | |
126 } |