memory_resource

// <experimental/memory_resource> -*- C++ -*-

// Copyright (C) 2015-2018 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 experimental/memory_resource
 *  This is a TS C++ Library header.
 */

#ifndef _GLIBCXX_EXPERIMENTAL_MEMORY_RESOURCE
#define _GLIBCXX_EXPERIMENTAL_MEMORY_RESOURCE 1

#include <memory>
#include <new>
#include <atomic>
#include <cstddef>
#include <bits/alloc_traits.h>
#include <experimental/bits/lfts_config.h>

namespace std {
_GLIBCXX_BEGIN_NAMESPACE_VERSION

namespace experimental {
inline namespace fundamentals_v2 {
namespace pmr {
#define __cpp_lib_experimental_memory_resources 201402L

  class memory_resource;

  template <typename _Tp>
    class polymorphic_allocator;

  template <typename _Alloc>
    class __resource_adaptor_imp;

  template <typename _Alloc>
    using resource_adaptor = __resource_adaptor_imp<
      typename allocator_traits<_Alloc>::template rebind_alloc<char>>;

  template <typename _Tp>
    struct __uses_allocator_construction_helper;

  // Global memory resources
  memory_resource* new_delete_resource() noexcept;
  memory_resource* null_memory_resource() noexcept;

  // The default memory resource
  memory_resource* get_default_resource() noexcept;
  memory_resource* set_default_resource(memory_resource* __r) noexcept;

  // Standard memory resources

  // 8.5 Class memory_resource
  class memory_resource
  {
  protected:
    static constexpr size_t _S_max_align = alignof(max_align_t);

  public:
    virtual ~memory_resource() { }

    void*
    allocate(size_t __bytes, size_t __alignment = _S_max_align)
    { return do_allocate(__bytes, __alignment); }

    void
    deallocate(void* __p, size_t __bytes, size_t __alignment = _S_max_align)
    { return do_deallocate(__p, __bytes, __alignment); }

    bool
    is_equal(const memory_resource& __other) const noexcept
    { return do_is_equal(__other); }

  protected:
    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;
  };

  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); }


  // 8.6 Class template polymorphic_allocator
  template <class _Tp>
    class polymorphic_allocator
    {
      using __uses_alloc1_ = __uses_alloc1<memory_resource*>;
      using __uses_alloc2_ = __uses_alloc2<memory_resource*>;

      template<typename _Tp1, typename... _Args>
	void
	_M_construct(__uses_alloc0, _Tp1* __p, _Args&&... __args)
	{ ::new(__p) _Tp1(std::forward<_Args>(__args)...); }

      template<typename _Tp1, typename... _Args>
	void
	_M_construct(__uses_alloc1_, _Tp1* __p, _Args&&...  __args)
	{ ::new(__p) _Tp1(allocator_arg, this->resource(),
			  std::forward<_Args>(__args)...); }

      template<typename _Tp1, typename... _Args>
	void
	_M_construct(__uses_alloc2_, _Tp1* __p, _Args&&...  __args)
	{ ::new(__p) _Tp1(std::forward<_Args>(__args)...,
			  this->resource()); }

    public:
      using value_type = _Tp;

      polymorphic_allocator() noexcept
      : _M_resource(get_default_resource())
      { }

      polymorphic_allocator(memory_resource* __r)
      : _M_resource(__r)
      { _GLIBCXX_DEBUG_ASSERT(__r); }

      polymorphic_allocator(const polymorphic_allocator& __other) = default;

      template <typename _Up>
	polymorphic_allocator(const polymorphic_allocator<_Up>&
			      __other) noexcept
	: _M_resource(__other.resource())
	{ }

      polymorphic_allocator&
	operator=(const polymorphic_allocator& __rhs) = default;

      _Tp* allocate(size_t __n)
      { return static_cast<_Tp*>(_M_resource->allocate(__n * sizeof(_Tp),
						       alignof(_Tp))); }

      void deallocate(_Tp* __p, size_t __n)
      { _M_resource->deallocate(__p, __n * sizeof(_Tp), alignof(_Tp)); }

      template <typename _Tp1, typename... _Args> //used here
	void construct(_Tp1* __p, _Args&&... __args)
	{
	  memory_resource* const __resource = this->resource();
	  auto __use_tag
	    = __use_alloc<_Tp1, memory_resource*, _Args...>(__resource);
	  _M_construct(__use_tag, __p, std::forward<_Args>(__args)...);
	}

      // Specializations for pair using piecewise construction
      template <typename _Tp1, typename _Tp2,
	       typename... _Args1, typename... _Args2>
	void construct(pair<_Tp1, _Tp2>* __p, piecewise_construct_t,
		       tuple<_Args1...> __x,
		       tuple<_Args2...> __y)
	{
	  memory_resource* const __resource = this->resource();
	  auto __x_use_tag =
	    __use_alloc<_Tp1, memory_resource*, _Args1...>(__resource);
	  auto __y_use_tag =
	    __use_alloc<_Tp2, memory_resource*, _Args2...>(__resource);

	  ::new(__p) std::pair<_Tp1, _Tp2>(piecewise_construct,
					   _M_construct_p(__x_use_tag, __x),
					   _M_construct_p(__y_use_tag, __y));
	}

      template <typename _Tp1, typename _Tp2>
	void construct(pair<_Tp1,_Tp2>* __p)
	{ this->construct(__p, piecewise_construct, tuple<>(), tuple<>()); }

      template <typename _Tp1, typename _Tp2, typename _Up, typename _Vp>
	void construct(pair<_Tp1,_Tp2>* __p, _Up&& __x, _Vp&& __y)
	{ this->construct(__p, piecewise_construct,
			  forward_as_tuple(std::forward<_Up>(__x)),
			  forward_as_tuple(std::forward<_Vp>(__y))); }

      template <typename _Tp1, typename _Tp2, typename _Up, typename _Vp>
	void construct(pair<_Tp1,_Tp2>* __p, const std::pair<_Up, _Vp>& __pr)
	{ this->construct(__p, piecewise_construct, forward_as_tuple(__pr.first),
			  forward_as_tuple(__pr.second)); }

      template <typename _Tp1, typename _Tp2, typename _Up, typename _Vp>
	void construct(pair<_Tp1,_Tp2>* __p, pair<_Up, _Vp>&& __pr)
	{ this->construct(__p, piecewise_construct,
			  forward_as_tuple(std::forward<_Up>(__pr.first)),
			  forward_as_tuple(std::forward<_Vp>(__pr.second))); }

      template <typename _Up>
	void destroy(_Up* __p)
	{ __p->~_Up(); }

      // Return a default-constructed allocator (no allocator propagation)
      polymorphic_allocator select_on_container_copy_construction() const
      { return polymorphic_allocator(); }

      memory_resource* resource() const
      { return _M_resource; }

    private:
      template<typename _Tuple>
	_Tuple&&
	_M_construct_p(__uses_alloc0, _Tuple& __t)
	{ return std::move(__t); }

      template<typename... _Args>
	decltype(auto)
	_M_construct_p(__uses_alloc1_ __ua, tuple<_Args...>& __t)
	{ return tuple_cat(make_tuple(allocator_arg, *(__ua._M_a)),
			   std::move(__t)); }

      template<typename... _Args>
	decltype(auto)
	_M_construct_p(__uses_alloc2_ __ua, tuple<_Args...>& __t)
	{ return tuple_cat(std::move(__t), make_tuple(*(__ua._M_a))); }

      memory_resource* _M_resource;
    };

  template <class _Tp1, class _Tp2>
    bool operator==(const polymorphic_allocator<_Tp1>& __a,
		    const polymorphic_allocator<_Tp2>& __b) noexcept
    { return *__a.resource() == *__b.resource(); }

  template <class _Tp1, class _Tp2>
    bool operator!=(const polymorphic_allocator<_Tp1>& __a,
		    const polymorphic_allocator<_Tp2>& __b) noexcept
    { return !(__a == __b); }

  // 8.7.1 __resource_adaptor_imp
  template <typename _Alloc>
    class __resource_adaptor_imp : public memory_resource
    {
    public:
      using allocator_type = _Alloc;

      __resource_adaptor_imp() = default;
      __resource_adaptor_imp(const __resource_adaptor_imp&) = default;
      __resource_adaptor_imp(__resource_adaptor_imp&&) = default;

      explicit __resource_adaptor_imp(const _Alloc& __a2)
      : _M_alloc(__a2)
      { }

      explicit __resource_adaptor_imp(_Alloc&& __a2)
      : _M_alloc(std::move(__a2))
      { }

      __resource_adaptor_imp&
      operator=(const __resource_adaptor_imp&) = default;

      allocator_type get_allocator() const { return _M_alloc; }

    protected:
      virtual void*
      do_allocate(size_t __bytes, size_t __alignment)
      {
	using _Aligned_alloc = std::__alloc_rebind<_Alloc, char>;
	size_t __new_size = _S_aligned_size(__bytes,
					    _S_supported(__alignment) ?
					    __alignment : _S_max_align);
	return _Aligned_alloc(_M_alloc).allocate(__new_size);
      }

      virtual void
      do_deallocate(void* __p, size_t __bytes, size_t __alignment)
      {
	using _Aligned_alloc = std::__alloc_rebind<_Alloc, char>;
	size_t __new_size = _S_aligned_size(__bytes,
					    _S_supported(__alignment) ?
					    __alignment : _S_max_align);
	using _Ptr = typename allocator_traits<_Aligned_alloc>::pointer;
	_Aligned_alloc(_M_alloc).deallocate(static_cast<_Ptr>(__p),
					    __new_size);
      }

      virtual bool
      do_is_equal(const memory_resource& __other) const noexcept
      {
	auto __p = dynamic_cast<const __resource_adaptor_imp*>(&__other);
	return __p ? (_M_alloc == __p->_M_alloc) : false;
      }

    private:
      // Calculate Aligned Size
      // Returns a size that is larger than or equal to __size and divisible
      // by __alignment, where __alignment is required to be the power of 2.
      static size_t
      _S_aligned_size(size_t __size, size_t __alignment)
      { return ((__size - 1)|(__alignment - 1)) + 1; }

      // Determine whether alignment meets one of those preconditions:
      // 1. Equals to Zero
      // 2. Is power of two
      static bool
      _S_supported (size_t __x)
      { return ((__x != 0) && !(__x & (__x - 1))); }

      _Alloc _M_alloc;
    };

  // Global memory resources
  inline std::atomic<memory_resource*>&
  __get_default_resource()
  {
    static atomic<memory_resource*> _S_default_resource(new_delete_resource());
    return _S_default_resource;
  }

  inline memory_resource*
  new_delete_resource() noexcept
  {
    static resource_adaptor<std::allocator<char>> __r;
    return static_cast<memory_resource*>(&__r);
  }

  template <typename _Alloc>
    class __null_memory_resource : private memory_resource
    {
    protected:
      void*
      do_allocate(size_t, size_t)
      { std::__throw_bad_alloc(); }

      void
      do_deallocate(void*, size_t, size_t) noexcept
      { }

      bool
      do_is_equal(const memory_resource& __other) const noexcept
      { return this == &__other; }

      friend memory_resource* null_memory_resource() noexcept;
    };

  inline memory_resource*
  null_memory_resource() noexcept
  {
    static __null_memory_resource<void> __r;
    return static_cast<memory_resource*>(&__r);
  }

  // The default memory resource
  inline memory_resource*
  get_default_resource() noexcept
  { return __get_default_resource().load(); }

  inline memory_resource*
  set_default_resource(memory_resource* __r) noexcept
  {
    if (__r == nullptr)
      __r = new_delete_resource();
    return __get_default_resource().exchange(__r);
  }
} // namespace pmr
} // namespace fundamentals_v2
} // namespace experimental

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif