I have some C++ code where I need to implement cache replacement using LRU technique.
So far I know two methods to implement LRU cache replacement:
So, which of these is better to be used in production code?
Are their any other better methods?
Recently I implemented a LRU cache using a linked list spread over a hash map.
/// Typedef for URL/Entry pair
typedef std::pair< std::string, Entry > EntryPair;
/// Typedef for Cache list
typedef std::list< EntryPair > CacheList;
/// Typedef for URL-indexed map into the CacheList
typedef boost::unordered_map< std::string, CacheList::iterator > CacheMap;
/// Cache LRU list
CacheList mCacheList;
/// Cache map into the list
CacheMap mCacheMap;
It has the advantage of being O(1) for all important operations.
The insertion algorithm:
// create new entry
Entry iEntry( ... );
// push it to the front;
mCacheList.push_front( std::make_pair( aURL, iEntry ) );
// add it to the cache map
mCacheMap[ aURL ] = mCacheList.begin();
// increase count of entries
mEntries++;
// check if it's time to remove the last element
if ( mEntries > mMaxEntries )
{
// erease from the map the last cache list element
mCacheMap.erase( mCacheList.back().first );
// erase it from the list
mCacheList.pop_back();
// decrease count
mEntries--;
}