lru_set.hpp

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#pragma once
 
/// @file userver/cache/lru_set.hpp
/// @brief @copybrief cache::LruSet
 
#include <userver/cache/impl/lru.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace cache {
 
/// @ingroup userver_universal userver_containers
///
/// LRU set, thread safety matches Standard Library thread safety
template <
    typename T,
    typename Hash = std::hash<impl::StringToStringView<T>>,
    typename Equal = std::equal_to<impl::StringToStringView<T>>>
class LruSet final {
public:
    explicit LruSet(size_t max_size, const Hash& hash = Hash(), const Equal& equal = Equal())
        : impl_(max_size, hash, equal)
    {}
 
    LruSet(LruSet&& lru) noexcept = default;
    LruSet(const LruSet& lru) = delete;
    LruSet& operator=(LruSet&& lru) noexcept = default;
    LruSet& operator=(const LruSet& lru) = delete;
 
    /// Adds key to the LRU or updates its usage
    /// @returns true if key is a new one
    bool Put(const T& key) { return impl_.Put(key, {}); }
 
    /// Removes key from LRU
    void Erase(const T& key) { return impl_.Erase(key); }
 
    /// Checks whether the key in LRU and updates its usage
    bool Has(const T& key) { return impl_.Get(key); }
 
    /// 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 Invalidate() { return impl_.Invalidate(); }
 
    /// Call Function(const T&) for all items
    template <typename Function>
    void VisitAll(Function&& func) const {
        impl_.VisitAll([&func](const auto& key, const auto& /*value*/) mutable { func(key); });
    }
 
    size_t GetSize() const { return impl_.GetSize(); }
 
    /// Returns pointer to the least recently used element
    /// or nullptr if LruSet is empty.
    /// @warning Returned pointer may be freed on the next set access!
    const T* GetLeastUsed() { return impl_.GetLeastUsedKey(); }
 
private:
    impl::LruBase<T, impl::EmptyPlaceholder, Hash, Equal> impl_;
};
 
}  // namespace cache
 
USERVER_NAMESPACE_END