common/lru/lru_cache.h

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

#include <list>
#include <unordered_map>

namespace resdb {

template <typename KeyType, typename ValueType>
class LRUCache {
 public:
  LRUCache(int capacity);
  ~LRUCache();

  ValueType Get(KeyType key);
  void Put(KeyType key, ValueType value);
  int GetCapacity();
  void SetCapacity(int new_capacity);
  void Flush();
  int GetCacheHits() const;
  int GetCacheMisses() const;
  double GetCacheHitRatio() const;

 private:
  int capacity_;
  int cache_hits_;
  int cache_misses_;
  std::list<KeyType> key_list_;  // Doubly linked list to store keys
  std::unordered_map<KeyType, ValueType>
      lookup_;  // Hash map for key-value pairs
  std::unordered_map<KeyType, typename std::list<KeyType>::iterator>
      rlookup_;  // Hash map for key-iterator pairs
};

}  // namespace resdb