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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/**
* Copyright (c) 2013-2014 Regents of the University of California.
*
* This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
*
* ndn-cxx library is free software: you can redistribute it and/or modify it under the
* terms of the GNU Lesser General Public License as published by the Free Software
* Foundation, either version 3 of the License, or (at your option) any later version.
*
* ndn-cxx library 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 Lesser General Public License for more details.
*
* You should have received copies of the GNU General Public License and GNU Lesser
* General Public License along with ndn-cxx, e.g., in COPYING.md file. If not, see
* <http://www.gnu.org/licenses/>.
*
* See AUTHORS.md for complete list of ndn-cxx authors and contributors.
*/
#ifndef NDN_UTIL_IN_MEMORY_STORAGE_LFU_HPP
#define NDN_UTIL_IN_MEMORY_STORAGE_LFU_HPP
#include "in-memory-storage.hpp"
#include <boost/multi_index/member.hpp>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/hashed_index.hpp>
#include <boost/multi_index/identity.hpp>
namespace ndn {
namespace util {
/** @brief Provides an in-memory storage with Least Frequently Used (LFU) replacement policy.
* @note The frequency right now is usage count.
* @sa https://en.wikipedia.org/w/index.php?title=Least_frequently_used&oldid=604542656
*/
class InMemoryStorageLfu : public InMemoryStorage
{
public:
explicit
InMemoryStorageLfu(size_t limit = 10);
virtual
~InMemoryStorageLfu();
NDN_CXX_PUBLIC_WITH_TESTS_ELSE_PROTECTED:
/** @brief Removes one Data packet from in-memory storage based on LFU, i.e. evict the least
* frequently accessed Data packet
* @return{ whether the Data was removed }
*/
virtual bool
evictItem();
/** @brief Update the entry when the entry is returned by the find() function,
* increment the frequency according to LFU
*/
virtual void
afterAccess(InMemoryStorageEntry* entry);
/** @brief Update the entry after a entry is successfully inserted, add it to the cleanupIndex
*/
virtual void
afterInsert(InMemoryStorageEntry* entry);
/** @brief Update the entry or other data structures before a entry is successfully erased,
* erase it from the cleanupIndex
*/
virtual void
beforeErase(InMemoryStorageEntry* entry);
private:
//binds frequency and entry together
struct CleanupEntry
{
InMemoryStorageEntry* entry;
uint64_t frequency;//could potentially be overflowed
};
/** @brief Function to increment frequency of the entry in the CleanupEntry
*/
static inline void
incrementFrequency(CleanupEntry& cleanupEntry)
{
++cleanupEntry.frequency;
}
private:
//multi_index_container to implement LFU
class byFrequency;
class byEntity;
typedef boost::multi_index_container<
CleanupEntry,
boost::multi_index::indexed_by<
// by Entry itself
boost::multi_index::hashed_unique<
boost::multi_index::tag<byEntity>,
boost::multi_index::member<CleanupEntry, InMemoryStorageEntry*, &CleanupEntry::entry>
>,
// by frequency (LFU)
boost::multi_index::ordered_non_unique<
boost::multi_index::tag<byFrequency>,
boost::multi_index::member<CleanupEntry, uint64_t, &CleanupEntry::frequency>,
std::less<uint64_t>
>
>
> CleanupIndex;
CleanupIndex m_cleanupIndex;
};
} // namespace util
} // namespace ndn
#endif // NDN_UTIL_IN_MEMORY_STORAGE_LFU_HPP