memory_resource_adapter.hpp

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// Copyright (C) 2015-2023 Jonathan Müller and foonathan/memory contributors
// SPDX-License-Identifier: Zlib
 
#ifndef WPI_MEMORY_MEMORY_RESOURCE_ADAPTER_HPP_INCLUDED
#define WPI_MEMORY_MEMORY_RESOURCE_ADAPTER_HPP_INCLUDED
 
/// \file
/// Class \ref wpi::memory::memory_resource_adapter and \ref wpi::memory::memory_resource_allocator to allow usage of PMRs.
 
#include "detail/assert.hpp"
#include "detail/utility.hpp"
#include "config.hpp"
#include "allocator_traits.hpp"
 
#if defined(__has_include) && __has_include(<memory_resource>)
 
#if !defined(__GNUC__) || __cplusplus >= 201703L
// The experimental/memory_resource header lacks a check for C++17 on older GCC,
// so we have to do it for them.
#include <memory_resource>
#endif
 
#elif defined(__has_include) && __has_include(<experimental/memory_resource>)
 
#if !defined(__GNUC__) || __cplusplus >= 201402L
// The experimental/memory_resource header lacks a check for C++14 on older GCC,
// so we have to do it for them.
#include <experimental/memory_resource>
#endif
 
#endif
 
#if defined(__cpp_lib_memory_resource)
 
// We use std::pmr::memory_resource.
namespace wpi_memory_pmr = std::pmr;
 
#elif defined(__cpp_lib_experimental_memory_resources)
 
// We use std::experimental::pmr::memory_resource.
namespace wpi_memory_pmr = std::experimental::pmr;
 
#else
 
// We use our own implementation.
namespace wpi_memory_pmr
{
    // see N3916 for documentation
    class memory_resource
    {
        static const std::size_t max_alignment = alignof(std::max_align_t);
 
    public:
        virtual ~memory_resource() noexcept {}
        void* allocate(std::size_t bytes, std::size_t alignment = max_alignment)
        {
            return do_allocate(bytes, alignment);
        }
        void deallocate(void* p, std::size_t bytes, std::size_t alignment = max_alignment)
        {
            do_deallocate(p, bytes, alignment);
        }
        bool is_equal(const memory_resource& other) const noexcept
        {
            return do_is_equal(other);
        }
 
    protected:
        virtual void* do_allocate(std::size_t bytes, std::size_t alignment)            = 0;
        virtual void  do_deallocate(void* p, std::size_t bytes, std::size_t alignment) = 0;
        virtual bool  do_is_equal(const memory_resource& other) const noexcept         = 0;
    };
    inline bool operator==(const memory_resource& a, const memory_resource& b) noexcept
    {
        return &a == &b || a.is_equal(b);
    }
    inline bool operator!=(const memory_resource& a, const memory_resource& b) noexcept
    {
        return !(a == b);
    }
} // namespace wpi_memory_pmr
 
#endif
 
namespace wpi
{
    namespace memory
    {
        /// The \c memory_resource abstract base class used in the implementation.
        /// \ingroup memory_adapter
        WPI_ALIAS_TEMPLATE(memory_resource, foonathan_memory_pmr::memory_resource);
 
        /// Wraps a RawAllocator and makes it a \ref memory_resource.
        /// \ingroup memory_adapter
        template <class RawAllocator>
        class memory_resource_adapter
        : public memory_resource,
          WPI_EBO(allocator_traits<RawAllocator>::allocator_type)
        {
        public:
            using allocator_type = typename allocator_traits<RawAllocator>::allocator_type;
 
            /// \effects Creates the resource by moving in the allocator.
            memory_resource_adapter(allocator_type&& other) noexcept
            : allocator_type(detail::move(other))
            {
            }
 
            /// @{
            /// \returns A reference to the wrapped allocator.
            allocator_type& get_allocator() noexcept
            {
                return *this;
            }
 
            const allocator_type& get_allocator() const noexcept
            {
                return *this;
            }
            /// @}
 
        protected:
            using traits_type = allocator_traits<RawAllocator>;
 
            /// \effects Allocates raw memory with given size and alignment.
            /// It forwards to \c allocate_node() or \c allocate_array() depending on the size.
            /// \returns The new memory as returned by the RawAllocator.
            /// \throws Anything thrown by the allocation function.
            void* do_allocate(std::size_t bytes, std::size_t alignment) override
            {
                auto max = traits_type::max_node_size(*this);
                if (bytes <= max)
                    return traits_type::allocate_node(*this, bytes, alignment);
                auto div = bytes / max;
                auto mod = bytes % max;
                auto n   = div + (mod != 0);
                return traits_type::allocate_array(*this, n, max, alignment);
            }
 
            /// \effects Deallocates memory previously allocated by \ref do_allocate.
            /// It forwards to \c deallocate_node() or \c deallocate_array() depending on the size.
            /// \throws Nothing.
            void do_deallocate(void* p, std::size_t bytes, std::size_t alignment) override
            {
                auto max = traits_type::max_node_size(*this);
                if (bytes <= max)
                    traits_type::deallocate_node(*this, p, bytes, alignment);
                else
                {
                    auto div = bytes / max;
                    auto mod = bytes % max;
                    auto n   = div + (mod != 0);
                    traits_type::deallocate_array(*this, p, n, max, alignment);
                }
            }
 
            /// \returns Whether or not \c *this is equal to \c other
            /// by comparing the addresses.
            bool do_is_equal(const memory_resource& other) const noexcept override
            {
                return this == &other;
            }
        };
 
        /// Wraps a \ref memory_resource and makes it a RawAllocator.
        /// \ingroup memory_adapter
        class memory_resource_allocator
        {
        public:
            /// \effects Creates it by giving it a pointer to the \ref memory_resource.
            /// \requires \c ptr must not be \c nullptr.
            memory_resource_allocator(memory_resource* ptr) noexcept : ptr_(ptr)
            {
                WPI_MEMORY_ASSERT(ptr);
            }
 
            /// \effects Allocates a node by forwarding to the \c allocate() function.
            /// \returns The node as returned by the \ref memory_resource.
            /// \throws Anything thrown by the \c allocate() function.
            void* allocate_node(std::size_t size, std::size_t alignment)
            {
                return ptr_->allocate(size, alignment);
            }
 
            /// \effects Deallocates a node by forwarding to the \c deallocate() function.
            void deallocate_node(void* ptr, std::size_t size, std::size_t alignment) noexcept
            {
                ptr_->deallocate(ptr, size, alignment);
            }
 
            /// \returns The maximum alignment which is the maximum value of type \c std::size_t.
            std::size_t max_alignment() const noexcept
            {
                return std::size_t(-1);
            }
 
            /// \returns A pointer to the used \ref memory_resource, this is never \c nullptr.
            memory_resource* resource() const noexcept
            {
                return ptr_;
            }
 
        private:
            memory_resource* ptr_;
        };
 
        /// @{
        /// \returns Whether `lhs` and `rhs` share the same resource.
        /// \relates memory_resource_allocator
        inline bool operator==(const memory_resource_allocator& lhs,
                               const memory_resource_allocator& rhs) noexcept
        {
            return lhs.resource() == rhs.resource();
        }
 
        inline bool operator!=(const memory_resource_allocator& lhs,
                               const memory_resource_allocator& rhs) noexcept
        {
            return !(lhs == rhs);
        }
        /// @}
 
#if !defined(DOXYGEN)
        template <class RawAllocator>
        struct is_shared_allocator;
#endif
 
        /// Specialization of \ref is_shared_allocator to mark \ref memory_resource_allocator as shared.
        /// This allows using it as \ref allocator_reference directly.
        /// \ingroup memory_adapter
        template <>
        struct is_shared_allocator<memory_resource_allocator> : std::true_type
        {
        };
    } // namespace memory
} // namespace wpi
 
#endif // WPI_MEMORY_MEMORY_RESOURCE_ADAPTER_HPP_INCLUDED