memory_resource.h

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// <memory_resource> -*- C++ -*-
 
// Copyright (C) 2018-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
 
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
 
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
/** @file include/bits/memory_resource.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{memory_resource}
 */
 
#ifndef _GLIBCXX_MEMORY_RESOURCE_H
#define _GLIBCXX_MEMORY_RESOURCE_H 1
 
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
 
#if __cplusplus >= 201703L
 
#include <new>                          // operator new(size_t, void*)
#include <cstddef>                      // size_t, max_align_t, byte
#include <bits/new_throw.h>             // __throw_bad_array_new_length
#include <bits/uses_allocator.h>        // allocator_arg_t, __use_alloc
#include <bits/uses_allocator_args.h>   // uninitialized_construct_using_alloc
#include <ext/numeric_traits.h>         // __int_traits
#include <debug/assertions.h>
 
#if ! __glibcxx_make_obj_using_allocator
# include <bits/utility.h>              // index_sequence
# include <tuple>                       // tuple, forward_as_tuple
#endif
#include <bits/memoryfwd.h>
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace pmr
{
  /// Class `memory_resource`
  /**
   * @ingroup pmr
   * @headerfile memory_resource
   * @since C++17
   */
  class memory_resource
  {
    static constexpr size_t _S_max_align = alignof(max_align_t);
 
  public:
    memory_resource() = default;
    memory_resource(const memory_resource&) = default;
    virtual ~memory_resource(); // key function
 
    memory_resource& operator=(const memory_resource&) = default;
 
    [[nodiscard]]
    void*
    allocate(size_t __bytes, size_t __alignment = _S_max_align)
    __attribute__((__returns_nonnull__,__alloc_size__(2),__alloc_align__(3)))
    { return ::operator new(__bytes, do_allocate(__bytes, __alignment)); }
 
    void
    deallocate(void* __p, size_t __bytes, size_t __alignment = _S_max_align)
    __attribute__((__nonnull__))
    { return do_deallocate(__p, __bytes, __alignment); }
 
    [[nodiscard]]
    bool
    is_equal(const memory_resource& __other) const noexcept
    { return do_is_equal(__other); }
 
  private:
    virtual void*
    do_allocate(size_t __bytes, size_t __alignment) = 0;
 
    virtual void
    do_deallocate(void* __p, size_t __bytes, size_t __alignment) = 0;
 
    virtual bool
    do_is_equal(const memory_resource& __other) const noexcept = 0;
  };
 
  [[nodiscard]]
  inline bool
  operator==(const memory_resource& __a, const memory_resource& __b) noexcept
  { return &__a == &__b || __a.is_equal(__b); }
 
#if __cpp_impl_three_way_comparison < 201907L
  [[nodiscard]]
  inline bool
  operator!=(const memory_resource& __a, const memory_resource& __b) noexcept
  { return !(__a == __b); }
#endif
 
  // C++17 23.12.3 Class template polymorphic_allocator
 
  /// Class template polymorphic_allocator
  /**
   * @ingroup pmr
   * @headerfile memory_resource
   * @since C++17
   */
  template<typename _Tp>
    class polymorphic_allocator
    {
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2975. Missing case for pair construction in polymorphic allocators
      template<typename _Up>
        struct __not_pair { using type = void; };
 
      template<typename _Up1, typename _Up2>
        struct __not_pair<pair<_Up1, _Up2>> { };
 
    public:
      using value_type = _Tp;
 
      polymorphic_allocator() noexcept
      {
        extern memory_resource* get_default_resource() noexcept
          __attribute__((__returns_nonnull__));
        _M_resource = get_default_resource();
      }
 
      polymorphic_allocator(memory_resource* __r) noexcept
      __attribute__((__nonnull__))
      : _M_resource(__r)
      { _GLIBCXX_DEBUG_ASSERT(__r); }
 
      polymorphic_allocator(const polymorphic_allocator& __other) = default;
 
      template<typename _Up>
        polymorphic_allocator(const polymorphic_allocator<_Up>& __x) noexcept
        : _M_resource(__x.resource())
        { }
 
      polymorphic_allocator&
      operator=(const polymorphic_allocator&) = delete;
 
      [[nodiscard]]
      _Tp*
      allocate(size_t __n)
      __attribute__((__returns_nonnull__))
      {
        if ((__gnu_cxx::__int_traits<size_t>::__max / sizeof(_Tp)) < __n)
          std::__throw_bad_array_new_length();
        return static_cast<_Tp*>(_M_resource->allocate(__n * sizeof(_Tp),
                                                       alignof(_Tp)));
      }
 
      void
      deallocate(_Tp* __p, size_t __n) noexcept
      __attribute__((__nonnull__))
      { _M_resource->deallocate(__p, __n * sizeof(_Tp), alignof(_Tp)); }
 
#ifdef __glibcxx_polymorphic_allocator // >= C++20
      [[nodiscard]] void*
      allocate_bytes(size_t __nbytes,
                     size_t __alignment = alignof(max_align_t))
      { return _M_resource->allocate(__nbytes, __alignment); }
 
      void
      deallocate_bytes(void* __p, size_t __nbytes,
                       size_t __alignment = alignof(max_align_t))
      { _M_resource->deallocate(__p, __nbytes, __alignment); }
 
      template<typename _Up>
        [[nodiscard]] _Up*
        allocate_object(size_t __n = 1)
        {
          if ((__gnu_cxx::__int_traits<size_t>::__max / sizeof(_Up)) < __n)
            std::__throw_bad_array_new_length();
          return static_cast<_Up*>(allocate_bytes(__n * sizeof(_Up),
                                                  alignof(_Up)));
        }
 
      template<typename _Up>
        void
        deallocate_object(_Up* __p, size_t __n = 1)
        { deallocate_bytes(__p, __n * sizeof(_Up), alignof(_Up)); }
 
      template<typename _Up, typename... _CtorArgs>
        [[nodiscard]] _Up*
        new_object(_CtorArgs&&... __ctor_args)
        {
          _Up* __p = allocate_object<_Up>();
          __try
            {
              construct(__p, std::forward<_CtorArgs>(__ctor_args)...);
            }
          __catch (...)
            {
              deallocate_object(__p);
              __throw_exception_again;
            }
          return __p;
        }
 
      template<typename _Up>
        void
        delete_object(_Up* __p)
        {
          __p->~_Up();
          deallocate_object(__p);
        }
#endif // C++20
 
#if ! __glibcxx_make_obj_using_allocator // >= C++20
      template<typename _Tp1, typename... _Args>
        __attribute__((__nonnull__))
        typename __not_pair<_Tp1>::type
        construct(_Tp1* __p, _Args&&... __args)
        {
          // _GLIBCXX_RESOLVE_LIB_DEFECTS
          // 2969. polymorphic_allocator::construct() shouldn't pass resource()
          using __use_tag
            = std::__uses_alloc_t<_Tp1, polymorphic_allocator, _Args...>;
          if constexpr (is_base_of_v<__uses_alloc0, __use_tag>)
            ::new(__p) _Tp1(std::forward<_Args>(__args)...);
          else if constexpr (is_base_of_v<__uses_alloc1_, __use_tag>)
            ::new(__p) _Tp1(allocator_arg, *this,
                            std::forward<_Args>(__args)...);
          else
            ::new(__p) _Tp1(std::forward<_Args>(__args)..., *this);
        }
 
      template<typename _Tp1, typename _Tp2,
               typename... _Args1, typename... _Args2>
        __attribute__((__nonnull__))
        void
        construct(pair<_Tp1, _Tp2>* __p, piecewise_construct_t,
                  tuple<_Args1...> __x, tuple<_Args2...> __y)
        {
          auto __x_tag =
            __use_alloc<_Tp1, polymorphic_allocator, _Args1...>(*this);
          auto __y_tag =
            __use_alloc<_Tp2, polymorphic_allocator, _Args2...>(*this);
          index_sequence_for<_Args1...> __x_i;
          index_sequence_for<_Args2...> __y_i;
 
          ::new(__p) pair<_Tp1, _Tp2>(piecewise_construct,
                                      _S_construct_p(__x_tag, __x_i, __x),
                                      _S_construct_p(__y_tag, __y_i, __y));
        }
 
      template<typename _Tp1, typename _Tp2>
        __attribute__((__nonnull__))
        void
        construct(pair<_Tp1, _Tp2>* __p)
        { this->construct(__p, piecewise_construct, tuple<>(), tuple<>()); }
 
      template<typename _Tp1, typename _Tp2, typename _Up, typename _Vp>
        __attribute__((__nonnull__))
        void
        construct(pair<_Tp1, _Tp2>* __p, _Up&& __x, _Vp&& __y)
        {
          this->construct(__p, piecewise_construct,
              std::forward_as_tuple(std::forward<_Up>(__x)),
              std::forward_as_tuple(std::forward<_Vp>(__y)));
        }
 
      template <typename _Tp1, typename _Tp2, typename _Up, typename _Vp>
        __attribute__((__nonnull__))
        void
        construct(pair<_Tp1, _Tp2>* __p, const std::pair<_Up, _Vp>& __pr)
        {
          this->construct(__p, piecewise_construct,
              std::forward_as_tuple(__pr.first),
              std::forward_as_tuple(__pr.second));
        }
 
      template<typename _Tp1, typename _Tp2, typename _Up, typename _Vp>
        __attribute__((__nonnull__))
        void
        construct(pair<_Tp1, _Tp2>* __p, pair<_Up, _Vp>&& __pr)
        {
          this->construct(__p, piecewise_construct,
              std::forward_as_tuple(std::forward<_Up>(__pr.first)),
              std::forward_as_tuple(std::forward<_Vp>(__pr.second)));
        }
#else // make_obj_using_allocator
      template<typename _Tp1, typename... _Args>
        __attribute__((__nonnull__))
        void
        construct(_Tp1* __p, _Args&&... __args)
        {
          std::uninitialized_construct_using_allocator(__p, *this,
              std::forward<_Args>(__args)...);
        }
#endif
 
      template<typename _Up>
        __attribute__((__nonnull__))
        void
        destroy(_Up* __p)
        { __p->~_Up(); }
 
      polymorphic_allocator
      select_on_container_copy_construction() const noexcept
      { return polymorphic_allocator(); }
 
      memory_resource*
      resource() const noexcept
      __attribute__((__returns_nonnull__))
      { return _M_resource; }
 
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 3683. operator== for polymorphic_allocator cannot deduce template arg
      [[nodiscard]]
      friend bool
      operator==(const polymorphic_allocator& __a,
                 const polymorphic_allocator& __b) noexcept
      { return *__a.resource() == *__b.resource(); }
 
#if __cpp_impl_three_way_comparison < 201907L
      [[nodiscard]]
      friend bool
      operator!=(const polymorphic_allocator& __a,
                 const polymorphic_allocator& __b) noexcept
      { return !(__a == __b); }
#endif
 
    private:
#if ! __glibcxx_make_obj_using_allocator // >= C++20
      using __uses_alloc1_ = __uses_alloc1<polymorphic_allocator>;
      using __uses_alloc2_ = __uses_alloc2<polymorphic_allocator>;
 
      template<typename _Ind, typename... _Args>
        static tuple<_Args&&...>
        _S_construct_p(__uses_alloc0, _Ind, tuple<_Args...>& __t)
        { return std::move(__t); }
 
      template<size_t... _Ind, typename... _Args>
        static tuple<allocator_arg_t, polymorphic_allocator, _Args&&...>
        _S_construct_p(__uses_alloc1_ __ua, index_sequence<_Ind...>,
                       tuple<_Args...>& __t)
        {
          return {
              allocator_arg, *__ua._M_a, std::get<_Ind>(std::move(__t))...
          };
        }
 
      template<size_t... _Ind, typename... _Args>
        static tuple<_Args&&..., polymorphic_allocator>
        _S_construct_p(__uses_alloc2_ __ua, index_sequence<_Ind...>,
                       tuple<_Args...>& __t)
        { return { std::get<_Ind>(std::move(__t))..., *__ua._M_a }; }
#endif
 
      memory_resource* _M_resource;
    };
 
  template<typename _Tp1, typename _Tp2>
    [[nodiscard]]
    inline bool
    operator==(const polymorphic_allocator<_Tp1>& __a,
               const polymorphic_allocator<_Tp2>& __b) noexcept
    { return *__a.resource() == *__b.resource(); }
 
#if __cpp_impl_three_way_comparison < 201907L
  template<typename _Tp1, typename _Tp2>
    [[nodiscard]]
    inline bool
    operator!=(const polymorphic_allocator<_Tp1>& __a,
               const polymorphic_allocator<_Tp2>& __b) noexcept
    { return !(__a == __b); }
#endif
 
} // namespace pmr
 
  template<typename _Alloc> struct allocator_traits;
 
  /// Partial specialization for `std::pmr::polymorphic_allocator`
  /**
   * @ingroup pmr
   * @headerfile memory_resource
   * @since C++17
   */
  template<typename _Tp>
    struct allocator_traits<pmr::polymorphic_allocator<_Tp>>
    {
      /// The allocator type
      using allocator_type = pmr::polymorphic_allocator<_Tp>;
 
      /// The allocated type
      using value_type = _Tp;
 
      /// The allocator's pointer type.
      using pointer = _Tp*;
 
      /// The allocator's const pointer type.
      using const_pointer = const _Tp*;
 
      /// The allocator's void pointer type.
      using void_pointer = void*;
 
      /// The allocator's const void pointer type.
      using const_void_pointer = const void*;
 
      /// The allocator's difference type
      using difference_type = std::ptrdiff_t;
 
      /// The allocator's size type
      using size_type = std::size_t;
 
      /** @{
       * A `polymorphic_allocator` does not propagate when a
       * container is copied, moved, or swapped.
       */
      using propagate_on_container_copy_assignment = false_type;
      using propagate_on_container_move_assignment = false_type;
      using propagate_on_container_swap = false_type;
 
      static allocator_type
      select_on_container_copy_construction(const allocator_type&) noexcept
      { return allocator_type(); }
      /// @}
 
      /// Whether all instances of the allocator type compare equal.
      using is_always_equal = false_type;
 
      template<typename _Up>
        using rebind_alloc = pmr::polymorphic_allocator<_Up>;
 
      template<typename _Up>
        using rebind_traits = allocator_traits<pmr::polymorphic_allocator<_Up>>;
 
      /**
       *  @brief  Allocate memory.
       *  @param  __a  An allocator.
       *  @param  __n  The number of objects to allocate space for.
       *
       *  Calls `a.allocate(n)`.
      */
      [[nodiscard]] static pointer
      allocate(allocator_type& __a, size_type __n)
      { return __a.allocate(__n); }
 
      /**
       *  @brief  Allocate memory.
       *  @param  __a  An allocator.
       *  @param  __n  The number of objects to allocate space for.
       *  @return Memory of suitable size and alignment for `n` objects
       *          of type `value_type`.
       *
       *  The third parameter is ignored..
       *
       *  Returns `a.allocate(n)`.
      */
      [[nodiscard]] static pointer
      allocate(allocator_type& __a, size_type __n, const_void_pointer)
      { return __a.allocate(__n); }
 
#ifdef __glibcxx_allocate_at_least
      /**
       *  @brief  Allocate memory.
       *  @param  __a  An allocator.
       *  @param  __n  The number of objects to allocate space for.
       *  @return Memory of suitable size and alignment for `n` objects
       *          of type `value_type`.
       *
       *  Just returns `{ a.allocate(n), n }`: `polymorphic_allocator`
       *  cannot be extended without breaking ABI.
      */
      [[nodiscard]] static std::allocation_result<pointer, size_type>
      allocate_at_least(allocator_type& __a, size_type __n)
      { return { __a.allocate(__n), __n }; }
#endif
 
      /**
       *  @brief  Deallocate memory.
       *  @param  __a  An allocator.
       *  @param  __p  Pointer to the memory to deallocate.
       *  @param  __n  The number of objects space was allocated for.
       *
       *  Calls `a.deallocate(p, n)`.
      */
      static void
      deallocate(allocator_type& __a, pointer __p, size_type __n)
      { __a.deallocate(__p, __n); }
 
      /**
       *  @brief  Construct an object of type `_Up`
       *  @param  __a  An allocator.
       *  @param  __p  Pointer to memory of suitable size and alignment for
       *               an object of type `_Up`.
       *  @param  __args Constructor arguments.
       *
       *  Calls `__a.construct(__p, std::forward<_Args>(__args)...)`
       *  in C++11, C++14 and C++17. Changed in C++20 to call
       *  `std::construct_at(__p, std::forward<_Args>(__args)...)` instead.
      */
      template<typename _Up, typename... _Args>
        static void
        construct(allocator_type& __a, _Up* __p, _Args&&... __args)
        { __a.construct(__p, std::forward<_Args>(__args)...); }
 
      /**
       *  @brief  Destroy an object of type `_Up`
       *  @param  __a  An allocator.
       *  @param  __p  Pointer to the object to destroy
       *
       *  Calls `p->_Up()`.
      */
      template<typename _Up>
        static _GLIBCXX20_CONSTEXPR void
        destroy(allocator_type&, _Up* __p)
        noexcept(is_nothrow_destructible<_Up>::value)
        { __p->~_Up(); }
 
      /**
       *  @brief  The maximum supported allocation size
       *  @return `numeric_limits<size_t>::max() / sizeof(value_type)`
      */
      static _GLIBCXX20_CONSTEXPR size_type
      max_size(const allocator_type&) noexcept
      { return size_t(-1) / sizeof(value_type); }
    };
 
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
 
#endif // C++17
#endif // _GLIBCXX_MEMORY_RESOURCE_H