Mercurial > hg > orthanc
view Core/Cache/LeastRecentlyUsedIndex.h @ 2810:1e8c4ecd02f4
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author | Sebastien Jodogne <s.jodogne@gmail.com> |
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date | Thu, 06 Sep 2018 11:06:54 +0200 |
parents | 878b59270859 |
children | 4e43e67f8ecf |
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/** * Orthanc - A Lightweight, RESTful DICOM Store * Copyright (C) 2012-2016 Sebastien Jodogne, Medical Physics * Department, University Hospital of Liege, Belgium * Copyright (C) 2017-2018 Osimis S.A., Belgium * * This program is free software: you can redistribute it and/or * modify it under the terms of the GNU General Public License as * published by the Free Software Foundation, either version 3 of the * License, or (at your option) any later version. * * In addition, as a special exception, the copyright holders of this * program give permission to link the code of its release with the * OpenSSL project's "OpenSSL" library (or with modified versions of it * that use the same license as the "OpenSSL" library), and distribute * the linked executables. You must obey the GNU General Public License * in all respects for all of the code used other than "OpenSSL". If you * modify file(s) with this exception, you may extend this exception to * your version of the file(s), but you are not obligated to do so. If * you do not wish to do so, delete this exception statement from your * version. If you delete this exception statement from all source files * in the program, then also delete it here. * * This program is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. **/ #pragma once #include <list> #include <map> #include <boost/noncopyable.hpp> #include <cassert> #include "../OrthancException.h" #include "../Toolbox.h" namespace Orthanc { /** * This class implements the index of a cache with least recently * used (LRU) recycling policy. All the items of the cache index * can be associated with a payload. * Reference: http://stackoverflow.com/a/2504317 **/ template <typename T, typename Payload = NullType> class LeastRecentlyUsedIndex : public boost::noncopyable { private: typedef std::list< std::pair<T, Payload> > Queue; typedef std::map<T, typename Queue::iterator> Index; Index index_; Queue queue_; /** * Internal method for debug builds to check whether the internal * data structures are not corrupted. **/ void CheckInvariants() const; public: /** * Add a new element to the cache index, and make it the most * recent element. * \param id The ID of the element. * \param payload The payload of the element. **/ void Add(T id, Payload payload = Payload()); void AddOrMakeMostRecent(T id, Payload payload = Payload()); /** * When accessing an element of the cache, this method tags the * element as the most recently used. * \param id The most recently accessed item. **/ void MakeMostRecent(T id); void MakeMostRecent(T id, Payload updatedPayload); /** * Remove an element from the cache index. * \param id The item to remove. **/ Payload Invalidate(T id); /** * Get the oldest element in the cache and remove it. * \return The oldest item. **/ T RemoveOldest(); /** * Get the oldest element in the cache, remove it and return the * associated payload. * \param payload Where to store the associated payload. * \return The oldest item. **/ T RemoveOldest(Payload& payload); /** * Check whether an element is contained in the cache. * \param id The item. * \return \c true iff the item is indexed by the cache. **/ bool Contains(T id) const { return index_.find(id) != index_.end(); } bool Contains(T id, Payload& payload) const { typename Index::const_iterator it = index_.find(id); if (it == index_.end()) { return false; } else { payload = it->second->second; return true; } } /** * Return the number of elements in the cache. * \return The number of elements. **/ size_t GetSize() const { assert(index_.size() == queue_.size()); return queue_.size(); } /** * Check whether the cache index is empty. * \return \c true iff the cache is empty. **/ bool IsEmpty() const { return index_.empty(); } const T& GetOldest() const; const Payload& GetOldestPayload() const; }; /****************************************************************** ** Implementation of the template ******************************************************************/ template <typename T, typename Payload> void LeastRecentlyUsedIndex<T, Payload>::CheckInvariants() const { #ifndef NDEBUG assert(index_.size() == queue_.size()); for (typename Index::const_iterator it = index_.begin(); it != index_.end(); it++) { assert(it->second != queue_.end()); assert(it->second->first == it->first); } #endif } template <typename T, typename Payload> void LeastRecentlyUsedIndex<T, Payload>::Add(T id, Payload payload) { if (Contains(id)) { throw OrthancException(ErrorCode_BadSequenceOfCalls); } queue_.push_front(std::make_pair(id, payload)); index_[id] = queue_.begin(); CheckInvariants(); } template <typename T, typename Payload> void LeastRecentlyUsedIndex<T, Payload>::MakeMostRecent(T id) { if (!Contains(id)) { throw OrthancException(ErrorCode_InexistentItem); } typename Index::iterator it = index_.find(id); assert(it != index_.end()); std::pair<T, Payload> item = *(it->second); queue_.erase(it->second); queue_.push_front(item); index_[id] = queue_.begin(); CheckInvariants(); } template <typename T, typename Payload> void LeastRecentlyUsedIndex<T, Payload>::AddOrMakeMostRecent(T id, Payload payload) { typename Index::iterator it = index_.find(id); if (it != index_.end()) { // Already existing. Make it most recent. std::pair<T, Payload> item = *(it->second); item.second = payload; queue_.erase(it->second); queue_.push_front(item); } else { // New item queue_.push_front(std::make_pair(id, payload)); } index_[id] = queue_.begin(); CheckInvariants(); } template <typename T, typename Payload> void LeastRecentlyUsedIndex<T, Payload>::MakeMostRecent(T id, Payload updatedPayload) { if (!Contains(id)) { throw OrthancException(ErrorCode_InexistentItem); } typename Index::iterator it = index_.find(id); assert(it != index_.end()); std::pair<T, Payload> item = *(it->second); item.second = updatedPayload; queue_.erase(it->second); queue_.push_front(item); index_[id] = queue_.begin(); CheckInvariants(); } template <typename T, typename Payload> Payload LeastRecentlyUsedIndex<T, Payload>::Invalidate(T id) { if (!Contains(id)) { throw OrthancException(ErrorCode_InexistentItem); } typename Index::iterator it = index_.find(id); assert(it != index_.end()); Payload payload = it->second->second; queue_.erase(it->second); index_.erase(it); CheckInvariants(); return payload; } template <typename T, typename Payload> T LeastRecentlyUsedIndex<T, Payload>::RemoveOldest(Payload& payload) { if (IsEmpty()) { throw OrthancException(ErrorCode_BadSequenceOfCalls); } std::pair<T, Payload> item = queue_.back(); T oldest = item.first; payload = item.second; queue_.pop_back(); assert(index_.find(oldest) != index_.end()); index_.erase(oldest); CheckInvariants(); return oldest; } template <typename T, typename Payload> T LeastRecentlyUsedIndex<T, Payload>::RemoveOldest() { if (IsEmpty()) { throw OrthancException(ErrorCode_BadSequenceOfCalls); } std::pair<T, Payload> item = queue_.back(); T oldest = item.first; queue_.pop_back(); assert(index_.find(oldest) != index_.end()); index_.erase(oldest); CheckInvariants(); return oldest; } template <typename T, typename Payload> const T& LeastRecentlyUsedIndex<T, Payload>::GetOldest() const { if (IsEmpty()) { throw OrthancException(ErrorCode_BadSequenceOfCalls); } return queue_.back().first; } template <typename T, typename Payload> const Payload& LeastRecentlyUsedIndex<T, Payload>::GetOldestPayload() const { if (IsEmpty()) { throw OrthancException(ErrorCode_BadSequenceOfCalls); } return queue_.back().second; } }