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comparison Core/MultiThreading/CacheIndex.h @ 282:915ed24547ea

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cache lru policy
author Sebastien Jodogne <s.jodogne@gmail.com>
date Wed, 12 Dec 2012 13:17:42 +0100
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children c9977db00e1d
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280:77e526e6fdf8 282:915ed24547ea
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 }