any_storage.hpp

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#pragma once
 
/// @file userver/utils/any_storage.hpp
/// @brief @copybrief utils::AnyStorage
 
#include <cstddef>
#include <memory>
#include <new>
#include <stdexcept>
#include <type_traits>
#include <vector>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
namespace any_storage::impl {
 
using Offset = std::size_t;
 
template <typename StorageTag>
inline Offset data_offset{0};
 
template <typename StorageTag>
inline std::size_t count{0};
 
template <typename StorageTag>
Offset RegisterData(std::size_t size, std::size_t alignment) noexcept {
    data_offset<StorageTag> += (alignment - (data_offset<StorageTag> % alignment)) % alignment;
    const Offset result = data_offset<StorageTag>;
    data_offset<StorageTag> += size;
 
    count<StorageTag> ++;
    return result;
}
 
void AssertStaticRegistrationAllowed();
 
template <typename T>
void Delete(std::byte* data) noexcept {
    std::destroy_at(reinterpret_cast<T*>(data));
}
 
}  // namespace any_storage::impl
 
template <typename StorageTag>
class AnyStorage;
 
template <typename StorageTag, typename Data>
class AnyStorageDataTag final {
public:
    AnyStorageDataTag() noexcept
        : number_(any_storage::impl::count<StorageTag>),
          offset_(any_storage::impl::RegisterData<StorageTag>(sizeof(Data), alignof(Data))) {
        static_assert(!std::is_reference_v<Data>);
        static_assert(!std::is_const_v<Data>);
        static_assert(
            __STDCPP_DEFAULT_NEW_ALIGNMENT__ >= alignof(Data),
            "Overaligned data members are not supported by AnyStorage"
        );
 
        any_storage::impl::AssertStaticRegistrationAllowed();
    }
 
private:
    const std::size_t number_;
    const any_storage::impl::Offset offset_;
 
    friend class AnyStorage<StorageTag>;
};
 
/// @ingroup userver_universal userver_containers
///
/// @brief map-like heterogeneous data storage
///
/// ## Usage example
/// @snippet utils/any_storage_test.cpp  AnyStorage
template <typename StorageTag>
class AnyStorage final {
public:
    AnyStorage();
 
    AnyStorage(AnyStorage&& other) noexcept = default;
    AnyStorage& operator=(AnyStorage&& other) noexcept;
    ~AnyStorage();
 
    /// @returns Stored data.
    template <typename Data>
    const Data& Get(const AnyStorageDataTag<StorageTag, Data>& tag) const;
 
    /// @returns Stored data.
    /// @throws std::runtime_error if no data was stored
    template <typename Data>
    Data& Get(const AnyStorageDataTag<StorageTag, Data>& tag);
 
    /// @brief Stores the data.
    template <typename Data>
    Data& Set(AnyStorageDataTag<StorageTag, Data> tag, Data data);
 
    /// @brief Emplaces the data. The data is rewritten if
    /// already stored.
    template <typename Data, typename... Args>
    Data& Emplace(const AnyStorageDataTag<StorageTag, Data>& tag, Args&&... args);
 
    /// @returns Pointer to stored data or nullptr if
    /// no data is found.
    template <typename Data>
    Data* GetOptional(const AnyStorageDataTag<StorageTag, Data>& tag) noexcept;
 
    /// @returns Pointer to stored data or nullptr if
    /// no data found.
    template <typename Data>
    const Data* GetOptional(const AnyStorageDataTag<StorageTag, Data>& tag) const noexcept;
 
    /// @brief Erase data.
    template <typename Data>
    void Erase(const AnyStorageDataTag<StorageTag, Data>& tag);
 
private:
    struct AllocRecord {
        void (*deleter)(std::byte*) noexcept;
        std::size_t offset;
    };
 
    AllocRecord* GetRecords() noexcept;
 
    static any_storage::impl::Offset CalcOffset() noexcept;
 
    void Destroy() noexcept;
 
    std::unique_ptr<std::byte[]> raw_data_;
};
 
template <typename StorageTag>
any_storage::impl::Offset AnyStorage<StorageTag>::CalcOffset() noexcept {
    const auto offset = any_storage::impl::data_offset<StorageTag>;
    return ((offset + alignof(AllocRecord) - 1) / alignof(AllocRecord)) * alignof(AllocRecord);
}
 
template <typename StorageTag>
AnyStorage<StorageTag>::AnyStorage()
    : raw_data_(new std::byte[CalcOffset() + sizeof(AllocRecord) * any_storage::impl::count<StorageTag>])
{
    static_assert(std::is_trivial_v<AllocRecord>);
 
    // NOLINTNEXTLINE(clang-analyzer-cplusplus.NewDeleteLeaks)
    auto records = GetRecords();
    for (std::size_t i = 0; i < any_storage::impl::count<StorageTag>; i++) {
        auto& record = records[i];
        record.deleter = nullptr;
    }
}
 
template <typename StorageTag>
AnyStorage<StorageTag>& AnyStorage<StorageTag>::operator=(AnyStorage&& other) noexcept {
    if (this != &other) {
        Destroy();
        raw_data_ = std::move(other.raw_data_);
    }
    return *this;
}
 
template <typename StorageTag>
AnyStorage<StorageTag>::~AnyStorage() {
    Destroy();
}
 
template <typename StorageTag>
void AnyStorage<StorageTag>::Destroy() noexcept {
    if (!raw_data_) {
        // moved out data
        return;
    }
 
    auto records = GetRecords();
 
    for (std::size_t i = 0; i < any_storage::impl::count<StorageTag>; i++) {
        auto& record = records[i];
        if (record.deleter) {
            record.deleter(&raw_data_[record.offset]);
        }
    }
}
 
template <typename StorageTag>
template <typename Data>
Data& AnyStorage<StorageTag>::Set(const AnyStorageDataTag<StorageTag, Data> tag, Data data) {
    auto number = tag.number_;
    if (!GetRecords()[number].deleter) {
        return Emplace(tag, std::move(data));
    }
 
    auto offset = tag.offset_;
    return *reinterpret_cast<Data*>(&raw_data_[offset]) = std::move(data);
}
 
template <typename StorageTag>
template <typename Data, typename... Args>
Data& AnyStorage<StorageTag>::Emplace(const AnyStorageDataTag<StorageTag, Data>& tag, Args&&... args) {
    auto number = tag.number_;
    auto& record = GetRecords()[number];
    if (record.deleter) {
        record.deleter(&raw_data_[tag.offset_]);
    }
 
    auto offset = tag.offset_;
    auto ptr = new (&raw_data_[offset]) Data(std::forward<Args>(args)...);
    record = {&any_storage::impl::Delete<Data>, offset};
    return *ptr;
}
 
template <typename StorageTag>
template <typename Data>
Data& AnyStorage<StorageTag>::Get(const AnyStorageDataTag<StorageTag, Data>& tag) {
    auto ptr = GetOptional(tag);
    if (ptr) {
        return *ptr;
    }
    throw std::runtime_error("No data");
}
 
template <typename StorageTag>
template <typename Data>
const Data& AnyStorage<StorageTag>::Get(const AnyStorageDataTag<StorageTag, Data>& tag) const {
    // NOLINTNEXTLINE(cppcoreguidelines-pro-type-const-cast)
    return const_cast<AnyStorage<StorageTag>*>(this)->Get<Data>(tag);
}
 
template <typename StorageTag>
template <typename Data>
Data* AnyStorage<StorageTag>::GetOptional(const AnyStorageDataTag<StorageTag, Data>& tag) noexcept {
    auto number = tag.number_;
    auto offset = tag.offset_;
    if (!GetRecords()[number].deleter) {
        return nullptr;
    }
    return reinterpret_cast<Data*>(&raw_data_[offset]);
}
 
template <typename StorageTag>
template <typename Data>
const Data* AnyStorage<StorageTag>::GetOptional(const AnyStorageDataTag<StorageTag, Data>& tag) const noexcept {
    // NOLINTNEXTLINE(cppcoreguidelines-pro-type-const-cast)
    return const_cast<AnyStorage*>(this)->GetOptional<Data>(tag);
}
 
template <typename StorageTag>
typename AnyStorage<StorageTag>::AllocRecord* AnyStorage<StorageTag>::GetRecords() noexcept {
    return reinterpret_cast<AllocRecord*>(&raw_data_[CalcOffset()]);
}
 
}  // namespace utils
 
USERVER_NAMESPACE_END