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1 /**
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2 * Orthanc - A Lightweight, RESTful DICOM Store
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3 * Copyright (C) 2012 Medical Physics Department, CHU of Liege,
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4 * Belgium
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5 *
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6 * This program is free software: you can redistribute it and/or
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7 * modify it under the terms of the GNU General Public License as
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8 * published by the Free Software Foundation, either version 3 of the
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9 * License, or (at your option) any later version.
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10 *
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11 * In addition, as a special exception, the copyright holders of this
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12 * program give permission to link the code of its release with the
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13 * OpenSSL project's "OpenSSL" library (or with modified versions of it
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14 * that use the same license as the "OpenSSL" library), and distribute
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15 * the linked executables. You must obey the GNU General Public License
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16 * in all respects for all of the code used other than "OpenSSL". If you
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17 * modify file(s) with this exception, you may extend this exception to
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18 * your version of the file(s), but you are not obligated to do so. If
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19 * you do not wish to do so, delete this exception statement from your
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20 * version. If you delete this exception statement from all source files
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21 * in the program, then also delete it here.
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22 *
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23 * This program is distributed in the hope that it will be useful, but
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24 * WITHOUT ANY WARRANTY; without even the implied warranty of
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25 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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26 * General Public License for more details.
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27 *
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28 * You should have received a copy of the GNU General Public License
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29 * along with this program. If not, see <http://www.gnu.org/licenses/>.
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30 **/
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31
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32
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33 #pragma once
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34
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35 #include <list>
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36 #include <map>
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37 #include <boost/noncopyable.hpp>
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38
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39 namespace Orthanc
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40 {
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41 class NullType
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42 {
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43 };
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44
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45 /**
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46 * This class implements the index of a cache with least recently
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47 * used (LRU) recycling policy. All the items of the cache index
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48 * can be associated with a payload.
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49 * Reference: http://stackoverflow.com/a/2504317
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50 **/
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51 template <typename T, typename Payload = NullType>
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52 class CacheIndex : public boost::noncopyable
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53 {
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54 private:
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55 typedef std::list< std::pair<T, Payload> > Queue;
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56 typedef std::map<T, typename Queue::iterator> Index;
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57
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58 Index index_;
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59 Queue queue_;
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60
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61 /**
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62 * Internal method for debug builds to check whether the internal
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63 * data structures are not corrupted.
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64 **/
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65 void CheckInvariants() const;
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66
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67 public:
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68 /**
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69 * Add a new element to the cache index, and make it the most
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70 * recent element.
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71 * \param id The ID of the element.
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72 * \param payload The payload of the element.
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73 **/
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74 void Add(T id, Payload payload = Payload());
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75
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76 /**
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77 * When accessing an element of the cache, this method tags the
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78 * element as the most recently used.
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79 * \param id The most recently accessed item.
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80 **/
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81 void TagAsMostRecent(T id);
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82
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83 /**
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84 * Remove an element from the cache index.
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85 * \param id The item to remove.
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86 **/
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87 Payload Invalidate(T id);
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88
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89 /**
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90 * Get the oldest element in the cache and remove it.
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91 * \return The oldest item.
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92 **/
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93 T RemoveOldest()
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94 {
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95 Payload p;
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96 return RemoveOldest(p);
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97 }
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98
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99 /**
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100 * Get the oldest element in the cache, remove it and return the
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101 * associated payload.
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102 * \param payload Where to store the associated payload.
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103 * \return The oldest item.
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104 **/
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105 T RemoveOldest(Payload& payload);
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106
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107 /**
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108 * Check whether an element is contained in the cache.
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109 * \param id The item.
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110 * \return \c true iff the item is indexed by the cache.
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111 **/
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112 bool Contains(T id) const
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113 {
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114 return index_.find(id) != index_.end();
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115 }
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116
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117 /**
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118 * Check whether the cache index is empty.
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119 * \return \c true iff the cache is empty.
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120 **/
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121 bool IsEmpty() const
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122 {
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123 return index_.empty();
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124 }
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125 };
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126 }
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