xref: /aosp_15_r20/external/ublksrv/qcow2/lrucache.hpp (revision 94c4a1e103eb1715230460aab379dff275992c20)

/*
 * File:   lrucache.hpp
 * Author: Alexander Ponomarev
 *
 * Created on June 20, 2013, 5:09 PM
 */

/*
 * Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are met:

 * Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer.

 * Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

 * Neither the name of lamerman nor the names of its
   contributors may be used to endorse or promote products derived from
   this software without specific prior written permission.

 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#ifndef _LRUCACHE_HPP_INCLUDED_
#define	_LRUCACHE_HPP_INCLUDED_

#include <unordered_map>
#include <list>
#include <cstddef>
#include <stdexcept>

namespace cache {

template<typename key_t, typename value_t>
class lru_cache {
public:
	typedef typename std::pair<key_t, value_t> key_value_pair_t;
	typedef typename std::list<key_value_pair_t>::iterator list_iterator_t;

	lru_cache(size_t max_size) :
		_max_size(max_size) {
	}

	value_t remove_last() {
		auto last = _cache_items_list.end();
		last--;
		auto t = last->second;
		_cache_items_map.erase(last->first);
		_cache_items_list.pop_back();

		return t;
	}

	value_t put(const key_t& key, const value_t& value) {
		auto it = _cache_items_map.find(key);
		_cache_items_list.push_front(key_value_pair_t(key, value));
		if (it != _cache_items_map.end()) {
			_cache_items_list.erase(it->second);
			_cache_items_map.erase(it);
		}
		_cache_items_map[key] = _cache_items_list.begin();

		if (_cache_items_map.size() > _max_size) {
			auto t = remove_last();
			return t;
		} else {
			//throw std::range_error("no cache dropped from put");
			return nullptr;
		}
	}

	//just retrieve value without updating position in the lru list
	value_t __get(const key_t& key) {
		auto it = _cache_items_map.find(key);
		if (it == _cache_items_map.end())
			return nullptr;
		else
			return it->second->second;
	}

	value_t get(const key_t& key) {
		auto it = _cache_items_map.find(key);
		if (it == _cache_items_map.end()) {
			//throw std::range_error("There is no such key in cache");
			return nullptr;
		} else {
			_cache_items_list.splice(_cache_items_list.begin(), _cache_items_list, it->second);
			return it->second->second;
		}
	}

	bool exists(const key_t& key) const {
		return _cache_items_map.find(key) != _cache_items_map.end();
	}

	size_t size() const {
		return _cache_items_map.size();
	}

	const std::list<key_value_pair_t>& get_lru_list_ro() const {
		return _cache_items_list;
	}

private:
	std::list<key_value_pair_t> _cache_items_list;
	std::unordered_map<key_t, list_iterator_t> _cache_items_map;
	size_t _max_size;
};

} // namespace cache

#endif	/* _LRUCACHE_HPP_INCLUDED_ */