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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,83 @@ | ||
| #pragma once | ||
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| #include <functional> | ||
| #include <list> | ||
| #include <mutex> | ||
| #include <optional> | ||
| #include <shared_mutex> | ||
| #include <unordered_map> | ||
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| namespace sisl { | ||
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| /** | ||
| * | ||
| * written by @jiankun | ||
| * | ||
| * A high performance LRU cache implementation. | ||
| * | ||
| * The cache provides two atomic operations: | ||
| * put(key, value): put an object into the cache. | ||
| * get(key): returns a optional reference to the value found by key in cache | ||
| * | ||
| * Important notes: | ||
| * 1. The get() method returns a const reference, any change to the reference | ||
| * needs to be done by a Put call. | ||
| * 2. The put/get methods are thread safe. | ||
| */ | ||
| template < typename key_t, typename value_t > | ||
| class LRUCache { | ||
| public: | ||
| using kv_pair_t = std::pair< key_t, value_t >; | ||
| using list_iterator_t = typename std::list< kv_pair_t >::iterator; | ||
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| explicit LRUCache(size_t capacity) : capacity_(capacity) {} | ||
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| template < typename K, typename V > | ||
| void put(K&& key, V&& value) { | ||
| std::unique_lock< std::shared_mutex > l{mtx_}; | ||
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| auto it = items_map_.find(key); | ||
| if (it != items_map_.end()) { | ||
| items_list_.erase(it->second); | ||
| items_map_.erase(it); | ||
| } | ||
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| items_list_.emplace_front(std::make_pair(std::forward< K >(key), std::forward< V >(value))); | ||
| items_map_[key] = items_list_.begin(); | ||
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| if (items_map_.size() > capacity_) { | ||
| auto last = items_list_.rbegin(); | ||
| items_map_.erase(last->first); | ||
| items_list_.pop_back(); | ||
| } | ||
| } | ||
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| [[nodiscard]] std::optional< value_t > get(const key_t& key) { | ||
| // we need unique lock for the splice operation | ||
| std::unique_lock< std::shared_mutex > l{mtx_}; | ||
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| auto it = items_map_.find(key); | ||
| if (it == items_map_.end()) { return std::nullopt; } | ||
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| items_list_.splice(items_list_.begin(), items_list_, it->second); | ||
| return std::optional(it->second->second); | ||
| } | ||
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| bool exists(const key_t& key) const { | ||
| std::shared_lock< std::shared_mutex > l{mtx_}; | ||
| return items_map_.find(key) != items_map_.end(); | ||
| } | ||
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| [[nodiscard]] size_t size() const { | ||
| std::shared_lock< std::shared_mutex > l{mtx_}; | ||
| return items_map_.size(); | ||
| } | ||
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| private: | ||
| std::list< kv_pair_t > items_list_; | ||
| std::unordered_map< key_t, list_iterator_t > items_map_; | ||
| size_t capacity_; | ||
| mutable std::shared_mutex mtx_; | ||
| }; | ||
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| } // namespace sisl |
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