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Better LRU Cache implementation

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DennisOSRM 2011-12-13 13:59:01 +01:00
parent e849d18c1b
commit a04eb2bba1
1 changed files with 58 additions and 113 deletions
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171
DataStructures/LRUCache.h
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@ -1,127 +1,72 @@
#include <climits>
#include <iostream>
#include <list>
#include <vector>
/*
open source routing machine
Copyright (C) Dennis Luxen, others 2010
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU AFFERO General Public License as published by
the Free Software Foundation; either version 3 of the License, or
any later version.
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 Affero General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
or see http://www.gnu.org/licenses/agpl.txt.
*/
#ifndef LRUCACHE_H
#define LRUCACHE_H
#include <list>
#include <boost/unordered_map.hpp>
template < class T >
struct Countfn {
unsigned long operator()( const T &x ) { return 1; }
};
template< class Key, class Data, class Sizefn = Countfn< Data > > class LRUCache {
public:
typedef std::list< std::pair< Key, Data > > List; ///< Main cache storage typedef
typedef typename List::iterator List_Iter; ///< Main cache iterator
typedef typename List::const_iterator List_cIter; ///< Main cache iterator (const)
typedef std::vector< Key > Key_List; ///< List of keys
typedef typename Key_List::iterator Key_List_Iter; ///< Main cache iterator
typedef typename Key_List::const_iterator Key_List_cIter; ///< Main cache iterator (const)
typedef boost::unordered_map< Key, List_Iter > Map; ///< Index typedef
typedef std::pair< Key, List_Iter > Pair; ///< Pair of Map elements
typedef typename Map::iterator Map_Iter; ///< Index iterator
typedef typename Map::const_iterator Map_cIter; ///< Index iterator (const)
template<typename ValueT>
class LRUCache {
private:
List _list; ///< Main cache storage
Map _index; ///< Cache storage index
unsigned long _max_size; ///< Maximum abstract size of the cache
unsigned long _curr_size; ///< Current abstract size of the cache
public:
LRUCache( const unsigned long Size ) : _max_size( Size ), _curr_size( 0 ) { }
~LRUCache() { clear(); }
inline const unsigned long size( void ) const { return _curr_size; }
inline const unsigned long max_size( void ) const { return _max_size; }
/// Clears all storage and indices.
void clear( void ) {
_list.clear();
_index.clear();
struct CacheEntry {
CacheEntry(unsigned k, ValueT v) : key(k), value(v) {}
unsigned key;
ValueT value;
};
unsigned capacity;
std::list<CacheEntry> itemsInCache;
boost::unordered_map<unsigned, typename std::list<CacheEntry>::iterator > positionMap;
public:
LRUCache(unsigned c) : capacity(c) {}
inline bool exists( const Key &key ) const {
return _index.find( key ) != _index.end();
bool Holds(unsigned key) {
if(positionMap.find(key) != positionMap.end()) {
return true;
}
return false;
}
inline void remove( const Key &key ) {
Map_Iter miter = _index.find( key );
if( miter == _index.end() ) return;
_remove( miter );
}
inline void touch( const Key &key ) {
_touch( key );
}
inline Data *fetch_ptr( const Key &key, bool touch = true ) {
Map_Iter miter = _index.find( key );
if( miter == _index.end() ) return NULL;
_touch( key );
return &(miter->second->second);
}
inline bool fetch( const Key &key, Data &data, bool touch_data = true ) {
Map_Iter miter = _index.find( key );
if( miter == _index.end() ) return false;
if( touch_data )
_touch( key );
data = miter->second->second;
return true;
}
inline void insert( const Key &key, const Data data ) {
// Touch the key, if it exists, then replace the content.
Map_Iter miter = _touch( key );
if( miter != _index.end() )
_remove( miter );
// Ok, do the actual insert at the head of the list
_list.push_front( std::make_pair( key, data ) );
List_Iter liter = _list.begin();
// Store the index
_index.insert( std::make_pair( key, liter ) );
_curr_size += Sizefn()( data );
// Check to see if we need to remove an element due to exceeding max_size
while( _curr_size > _max_size ) {
std::cout << "removing element " << std::endl;
// Remove the last element.
liter = _list.end();
--liter;
_remove( liter->first );
void Insert(const unsigned key, ValueT value) {
itemsInCache.push_front(CacheEntry(key, value));
positionMap.insert(std::make_pair(key, itemsInCache.begin()));
if(itemsInCache.size() > capacity) {
positionMap.erase(itemsInCache.back().key);
itemsInCache.pop_back();
}
}
bool Fetch(const unsigned key, ValueT& result) {
if(Holds(key)) {
CacheEntry e = *(positionMap.find(key)->second);
result = e.value;
inline const Key_List get_all_keys( void ) {
Key_List ret;
for( List_cIter liter = _list.begin(); liter != _list.end(); liter++ )
ret.push_back( liter->first );
return ret;
//move to front
itemsInCache.splice(positionMap.find(key)->second, itemsInCache, itemsInCache.begin());
positionMap.find(key)->second = itemsInCache.begin();
return true;
}
return false;
}
private:
inline Map_Iter _touch( const Key &key ) {
Map_Iter miter = _index.find( key );
if( miter == _index.end() ) return miter;
// Move the found node to the head of the list.
_list.splice( _list.begin(), _list, miter->second );
return miter;
}
inline void _remove( const Map_Iter &miter ) {
_curr_size -= Sizefn()( miter->second->second );
_list.erase( miter->second );
_index.erase( miter );
}
inline void _remove( const Key &key ) {
Map_Iter miter = _index.find( key );
_remove( miter );
unsigned Size() const {
return itemsInCache.size();
}
};
#endif //LRUCACHE_H