in-memory-storage-lfu.hpp

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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
#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 {

class InMemoryStorageLfu : public InMemoryStorage
{
public:
  explicit
  InMemoryStorageLfu(size_t limit = 10);

  explicit
  InMemoryStorageLfu(boost::asio::io_service& ioService, size_t limit = 10);

NDN_CXX_PUBLIC_WITH_TESTS_ELSE_PROTECTED:
  virtual bool
  evictItem() override;

  virtual void
  afterAccess(InMemoryStorageEntry* entry) override;

  virtual void
  afterInsert(InMemoryStorageEntry* entry) override;

  virtual void
  beforeErase(InMemoryStorageEntry* entry) override;

private:
  // binds frequency and entry together
  struct CleanupEntry
  {
    InMemoryStorageEntry* entry;
    uint64_t frequency; // could potentially be overflowed
  };

  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