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LRUStrategy.h
//
// LRUStrategy.h
//
// $Id: //poco/1.4/Foundation/include/Poco/LRUStrategy.h#1 $
//
// Library: Foundation
// Package: Cache
// Module:  LRUStrategy
//
// Definition of the LRUStrategy class.
//
// Copyright (c) 2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_LRUStrategy_INCLUDED
#define Foundation_LRUStrategy_INCLUDED


#include "Poco/KeyValueArgs.h"
#include "Poco/ValidArgs.h"
#include "Poco/AbstractStrategy.h"
#include "Poco/EventArgs.h"
#include "Poco/Exception.h"
#include <list>
#include <map>
#include <cstddef>


namespace Poco {


template <class TKey, class TValue>
00057 class LRUStrategy: public AbstractStrategy<TKey, TValue>
      /// An LRUStrategy implements least recently used cache replacement.
{
public:
      typedef std::list<TKey>                   Keys;
      typedef typename Keys::iterator           Iterator;
      typedef typename Keys::const_iterator     ConstIterator;
      typedef std::map<TKey, Iterator>          KeyIndex;
      typedef typename KeyIndex::iterator       IndexIterator;
      typedef typename KeyIndex::const_iterator ConstIndexIterator;

public:
      LRUStrategy(std::size_t size): 
            _size(size)
      {
            if (_size < 1) throw InvalidArgumentException("size must be > 0");
      }

      ~LRUStrategy()
      {
      }

      void onAdd(const void*, const KeyValueArgs <TKey, TValue>& args)
      {
            _keys.push_front(args.key());
            std::pair<IndexIterator, bool> stat = _keyIndex.insert(std::make_pair(args.key(), _keys.begin()));
            if (!stat.second)
            {
                  stat.first->second = _keys.begin();
            }
      }

00089       void onRemove(const void*, const TKey& key)
      {
            IndexIterator it = _keyIndex.find(key);

            if (it != _keyIndex.end())
            {
                  _keys.erase(it->second);
                  _keyIndex.erase(it);
            }
      }

00100       void onGet(const void*, const TKey& key)
      {
            // LRU: in case of an hit, move to begin
            IndexIterator it = _keyIndex.find(key);

            if (it != _keyIndex.end())
            {
                  _keys.splice(_keys.begin(), _keys, it->second); //_keys.erase(it->second)+_keys.push_front(key);
                  it->second = _keys.begin();
            }
      }

00112       void onClear(const void*, const EventArgs& args)
      {
            _keys.clear();
            _keyIndex.clear();
      }

00118       void onIsValid(const void*, ValidArgs<TKey>& args)
      {
            if (_keyIndex.find(args.key()) == _keyIndex.end())
            {
                  args.invalidate();
            }
      }

00126       void onReplace(const void*, std::set<TKey>& elemsToRemove)
      {
            // Note: replace only informs the cache which elements
            // it would like to remove!
            // it does not remove them on its own!
            std::size_t curSize = _keyIndex.size();

            if (curSize < _size)
            {
                  return;
            }

            std::size_t diff = curSize - _size;
            Iterator it = --_keys.end(); //--keys can never be invoked on an empty list due to the minSize==1 requirement of LRU
            std::size_t i = 0;

            while (i++ < diff) 
            {
                  elemsToRemove.insert(*it);
                  if (it != _keys.begin())
                  {
                        --it;
                  }
            }
      }

protected:
      std::size_t _size;     /// Number of keys the cache can store.
00154       Keys        _keys;
      KeyIndex    _keyIndex; /// For faster access to _keys
};


} // namespace Poco


#endif // Foundation_LRUStrategy_INCLUDED

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