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/******************************************************************************
*
* Copyright 2020 Google, Inc.
*
* Licensed 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.
*
******************************************************************************/
#pragma once
#include <functional>
#include <iterator>
#include <list>
#include <mutex>
#include <optional>
#include <thread>
#include <unordered_map>
#include <base/logging.h>
#include "check.h"
namespace bluetooth {
namespace common {
template <typename K, typename V>
class LegacyLruCache {
public:
using Node = std::pair<K, V>;
/**
* Constructor of the cache
*
* @param capacity maximum size of the cache
* @param log_tag, keyword to put at the head of log.
*/
LegacyLruCache(const size_t& capacity, const std::string& log_tag)
: capacity_(capacity) {
if (capacity_ == 0) {
// don't allow invalid capacity
LOG(FATAL) << log_tag << " unable to have 0 LRU Cache capacity";
}
}
// delete copy constructor
LegacyLruCache(LegacyLruCache const&) = delete;
LegacyLruCache& operator=(LegacyLruCache const&) = delete;
~LegacyLruCache() { Clear(); }
/**
* Clear the cache
*/
void Clear() {
std::lock_guard<std::recursive_mutex> lock(lru_mutex_);
lru_map_.clear();
node_list_.clear();
}
/**
* Same as Get, but return an iterator to the accessed element
*
* Modifying the returned iterator does not warm up the cache
*
* @param key
* @return pointer to the underlying value to allow in-place modification
* nullptr when not found, will be invalidated when the key is evicted
*/
V* Find(const K& key) {
std::lock_guard<std::recursive_mutex> lock(lru_mutex_);
auto map_iterator = lru_map_.find(key);
if (map_iterator == lru_map_.end()) {
return nullptr;
}
node_list_.splice(node_list_.begin(), node_list_, map_iterator->second);
return &(map_iterator->second->second);
}
/**
* Get the value of a key, and move the key to the head of cache, if there is
* one
*
* @param key
* @param value, output parameter of value of the key
* @return true if the cache has the key
*/
bool Get(const K& key, V* value) {
CHECK(value != nullptr);
std::lock_guard<std::recursive_mutex> lock(lru_mutex_);
auto value_ptr = Find(key);
if (value_ptr == nullptr) {
return false;
}
*value = *value_ptr;
return true;
}
/**
* Check if the cache has the input key, move the key to the head
* if there is one
*
* @param key
* @return true if the cache has the key
*/
bool HasKey(const K& key) {
std::lock_guard<std::recursive_mutex> lock(lru_mutex_);
return Find(key) != nullptr;
}
/**
* Put a key-value pair to the head of cache
*
* @param key
* @param value
* @return evicted node if tail value is popped, std::nullopt if no value
* is popped. std::optional can be treated as a boolean as well
*/
std::optional<Node> Put(const K& key, V value) {
std::lock_guard<std::recursive_mutex> lock(lru_mutex_);
auto value_ptr = Find(key);
if (value_ptr != nullptr) {
// hasKey() calls get(), therefore already move the node to the head
*value_ptr = std::move(value);
return std::nullopt;
}
// remove tail
std::optional<Node> ret = std::nullopt;
if (lru_map_.size() == capacity_) {
lru_map_.erase(node_list_.back().first);
ret = std::move(node_list_.back());
node_list_.pop_back();
}
// insert to dummy next;
node_list_.emplace_front(key, std::move(value));
lru_map_.emplace(key, node_list_.begin());
return ret;
}
/**
* Delete a key from cache
*
* @param key
* @return true if deleted successfully
*/
bool Remove(const K& key) {
std::lock_guard<std::recursive_mutex> lock(lru_mutex_);
auto map_iterator = lru_map_.find(key);
if (map_iterator == lru_map_.end()) {
return false;
}
// remove from the list
node_list_.erase(map_iterator->second);
// delete key from map
lru_map_.erase(map_iterator);
return true;
}
/**
* Return size of the cache
*
* @return size of the cache
*/
int Size() const {
std::lock_guard<std::recursive_mutex> lock(lru_mutex_);
return lru_map_.size();
}
private:
std::list<Node> node_list_;
size_t capacity_;
std::unordered_map<K, typename std::list<Node>::iterator> lru_map_;
mutable std::recursive_mutex lru_mutex_;
};
} // namespace common
} // namespace bluetooth
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