lru_map.hpp

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#pragma once
 
/// @file userver/cache/lru_map.hpp
/// @brief @copybrief cache::LruMap
 
#include <userver/cache/impl/lru.hpp>
 
USERVER_NAMESPACE_BEGIN
 
/// Utilities for caching
namespace cache {
 
/// @ingroup userver_universal userver_containers
///
/// LRU key value storage (LRU cache), thread safety matches Standard Library
/// thread safety
template <
    typename T,
    typename U,
    typename Hash = std::hash<impl::StringToStringView<T>>,
    typename Equal = std::equal_to<impl::StringToStringView<T>>>
class LruMap final {
public:
    explicit LruMap(size_t max_size, const Hash& hash = Hash(), const Equal& equal = Equal())
        : impl_(max_size, hash, equal) {}
 
    LruMap(LruMap&& lru) noexcept = default;
    LruMap(const LruMap& lru) = delete;
    LruMap& operator=(LruMap&& lru) noexcept = default;
    LruMap& operator=(const LruMap& lru) = delete;
 
    /// Adds or rewrites key/value, updates its usage
    /// @returns true if key is a new one
    bool Put(const T& key, U value) { return impl_.Put(key, std::move(value)); }
 
    /// Returns pointer to value if the key is in LRU and updates its usage;
    /// constructs and adds a new key/value otherwise.
    /// @warning Returned pointer may be freed on the next map access!
    template <typename... Args>
    U* Emplace(const T& key, Args&&... args) {
        return impl_.Emplace(key, std::forward<Args>(args)...);
    }
 
    /// Removes key from LRU
    void Erase(const T& key) { impl_.Erase(key); }
 
    /// Returns pointer to value if the key is in LRU and updates its usage;
    /// returns nullptr otherwise.
    /// @warning Returned pointer may be freed on the next map access!
    U* Get(const T& key) { return impl_.Get(key); }
 
    /// Returns pointer to value if the key is in LRU and updates its usage;
    /// returns nullptr otherwise.
    /// @warning Returned pointer may be freed on the next map access!
    template <class Key>
    U* GetTransparent(const Key& key) {
        return impl_.GetTransparent(key);
    }
 
    /// Returns value by key and updates its usage; returns default_value
    /// otherwise without modifying the cache.
    U GetOr(const T& key, const U& default_value) {
        auto* ptr = impl_.Get(key);
        if (ptr) return *ptr;
        return default_value;
    }
 
    /// Returns pointer to the least recently used value;
    /// returns nullptr if LRU is empty.
    /// @warning Returned pointer may be freed on the next map access!
    U* GetLeastUsed() { return impl_.GetLeastUsedValue(); }
 
    /// Sets the max size of the LRU, truncates values if new_max_size < GetSize()
    void SetMaxSize(size_t new_max_size) { return impl_.SetMaxSize(new_max_size); }
 
    /// Removes all the elements
    void Clear() { return impl_.Clear(); }
 
    /// Call Function(const T&, const U&) for all items
    template <typename Function>
    void VisitAll(Function&& func) const {
        impl_.VisitAll(std::forward<Function>(func));
    }
 
    /// Call Function(const T&, U&) for all items
    template <typename Function>
    void VisitAll(Function&& func) {
        impl_.VisitAll(std::forward<Function>(func));
    }
 
    size_t GetSize() const { return impl_.GetSize(); }
 
    std::size_t GetCapacity() const { return impl_.GetCapacity(); }
 
private:
    impl::LruBase<T, U, Hash, Equal> impl_;
};
 
}  // namespace cache
 
USERVER_NAMESPACE_END