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140 lines
3.3 KiB
C++
140 lines
3.3 KiB
C++
//
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// LRUStrategy.h
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//
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// Library: Foundation
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// Package: Cache
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// Module: LRUStrategy
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//
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// Definition of the LRUStrategy class.
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//
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// Copyright (c) 2006, Applied Informatics Software Engineering GmbH.
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// and Contributors.
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//
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// SPDX-License-Identifier: BSL-1.0
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//
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#ifndef Foundation_LRUStrategy_INCLUDED
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#define Foundation_LRUStrategy_INCLUDED
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#include <cstddef>
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#include <list>
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#include <map>
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#include "Poco/AbstractStrategy.h"
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#include "Poco/EventArgs.h"
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#include "Poco/Exception.h"
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#include "Poco/KeyValueArgs.h"
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#include "Poco/ValidArgs.h"
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namespace Poco
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{
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template <class TKey, class TValue>
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class LRUStrategy : public AbstractStrategy<TKey, TValue>
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/// An LRUStrategy implements least recently used cache replacement.
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{
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public:
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typedef std::list<TKey> Keys;
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typedef typename Keys::iterator Iterator;
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typedef typename Keys::const_iterator ConstIterator;
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typedef std::map<TKey, Iterator> KeyIndex;
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typedef typename KeyIndex::iterator IndexIterator;
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typedef typename KeyIndex::const_iterator ConstIndexIterator;
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public:
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LRUStrategy(std::size_t size) : _size(size)
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{
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if (_size < 1)
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throw InvalidArgumentException("size must be > 0");
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}
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~LRUStrategy() { }
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void onAdd(const void *, const KeyValueArgs<TKey, TValue> & args)
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{
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_keys.push_front(args.key());
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std::pair<IndexIterator, bool> stat = _keyIndex.insert(std::make_pair(args.key(), _keys.begin()));
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if (!stat.second)
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{
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stat.first->second = _keys.begin();
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}
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}
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void onRemove(const void *, const TKey & key)
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{
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IndexIterator it = _keyIndex.find(key);
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if (it != _keyIndex.end())
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{
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_keys.erase(it->second);
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_keyIndex.erase(it);
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}
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}
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void onGet(const void *, const TKey & key)
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{
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// LRU: in case of an hit, move to begin
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IndexIterator it = _keyIndex.find(key);
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if (it != _keyIndex.end())
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{
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_keys.splice(_keys.begin(), _keys, it->second); //_keys.erase(it->second)+_keys.push_front(key);
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it->second = _keys.begin();
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}
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}
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void onClear(const void *, const EventArgs & args)
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{
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_keys.clear();
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_keyIndex.clear();
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}
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void onIsValid(const void *, ValidArgs<TKey> & args)
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{
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if (_keyIndex.find(args.key()) == _keyIndex.end())
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{
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args.invalidate();
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}
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}
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void onReplace(const void *, std::set<TKey> & elemsToRemove)
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{
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// Note: replace only informs the cache which elements
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// it would like to remove!
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// it does not remove them on its own!
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std::size_t curSize = _keyIndex.size();
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if (curSize < _size)
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{
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return;
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}
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std::size_t diff = curSize - _size;
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Iterator it = --_keys.end(); /// --keys can never be invoked on an empty list due to the minSize==1 requirement of LRU
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std::size_t i = 0;
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while (i++ < diff)
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{
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elemsToRemove.insert(*it);
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if (it != _keys.begin())
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{
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--it;
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}
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}
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}
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protected:
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std::size_t _size; /// Number of keys the cache can store.
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Keys _keys;
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KeyIndex _keyIndex; /// For faster access to _keys
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};
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} // namespace Poco
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#endif // Foundation_LRUStrategy_INCLUDED
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