allocator.h
Go to the documentation of this file.
// Allocators -*- C++ -*-
// Copyright (C) 2001-2021 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/>.
/*
* Copyright (c) 1996-1997
* Silicon Graphics Computer Systems, Inc.
*
* Permission to use, copy, modify, distribute and sell this software
* and its documentation for any purpose is hereby granted without fee,
* provided that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice appear
* in supporting documentation. Silicon Graphics makes no
* representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied warranty.
*/
/** @file bits/allocator.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{memory}
*/
#ifndef _ALLOCATOR_H
#define _ALLOCATOR_H 1
#include <bits/c++allocator.h> // Define the base class to std::allocator.
#include <bits/memoryfwd.h>
#if __cplusplus >= 201103L
#include <type_traits>
#endif
#define __cpp_lib_incomplete_container_elements 201505
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @addtogroup allocators
* @{
*/
// Since C++20 the primary template should be used for allocator<void>,
// but then it would have a non-trivial default ctor and dtor for C++20,
// but trivial for C++98-17, which would be an ABI incompatibiliy between
// different standard dialects. So C++20 still uses the allocator<void>
// explicit specialization, with the historical ABI properties, but with
// the same members that are present in the primary template.
/// allocator<void> specialization.
template<>
class allocator<void>
{
public:
typedef void value_type;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
#if __cplusplus <= 201703L
// These were removed for C++20, allocator_traits does the right thing.
typedef void* pointer;
typedef const void* const_pointer;
template<typename _Tp1>
struct rebind
{ typedef allocator<_Tp1> other; };
#endif
#if __cplusplus >= 201103L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2103. std::allocator propagate_on_container_move_assignment
using propagate_on_container_move_assignment = true_type;
using is_always_equal
_GLIBCXX20_DEPRECATED_SUGGEST("allocator_traits::is_always_equal")
= true_type;
#if __cplusplus >= 202002L
// As noted above, these members are present for C++20 to provide the
// same API as the primary template, but still trivial as in pre-C++20.
allocator() = default;
~allocator() = default;
template<typename _Up>
constexpr
allocator(const allocator<_Up>&) noexcept { }
// No allocate member because it's ill-formed by LWG 3307.
// No deallocate member because it would be undefined to call it
// with any pointer which wasn't obtained from allocate.
#endif // C++20
#endif // C++11
};
/**
* @brief The @a standard allocator, as per C++03 [20.4.1].
*
* See https://gcc.gnu.org/onlinedocs/libstdc++/manual/memory.html#std.util.memory.allocator
* for further details.
*
* @tparam _Tp Type of allocated object.
*/
template<typename _Tp>
class allocator : public __allocator_base<_Tp>
{
public:
typedef _Tp value_type;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
#if __cplusplus <= 201703L
// These were removed for C++20.
typedef _Tp* pointer;
typedef const _Tp* const_pointer;
typedef _Tp& reference;
typedef const _Tp& const_reference;
template<typename _Tp1>
struct rebind
{ typedef allocator<_Tp1> other; };
#endif
#if __cplusplus >= 201103L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2103. std::allocator propagate_on_container_move_assignment
using propagate_on_container_move_assignment = true_type;
using is_always_equal
_GLIBCXX20_DEPRECATED_SUGGEST("allocator_traits::is_always_equal")
= true_type;
#endif
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3035. std::allocator's constructors should be constexpr
_GLIBCXX20_CONSTEXPR
allocator() _GLIBCXX_NOTHROW { }
_GLIBCXX20_CONSTEXPR
allocator(const allocator& __a) _GLIBCXX_NOTHROW
: __allocator_base<_Tp>(__a) { }
#if __cplusplus >= 201103L
// Avoid implicit deprecation.
allocator& operator=(const allocator&) = default;
#endif
template<typename _Tp1>
_GLIBCXX20_CONSTEXPR
allocator(const allocator<_Tp1>&) _GLIBCXX_NOTHROW { }
#if __cpp_constexpr_dynamic_alloc
constexpr
#endif
~allocator() _GLIBCXX_NOTHROW { }
#if __cplusplus > 201703L
[[nodiscard,__gnu__::__always_inline__]]
constexpr _Tp*
allocate(size_t __n)
{
#ifdef __cpp_lib_is_constant_evaluated
if (std::is_constant_evaluated())
return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp)));
#endif
return __allocator_base<_Tp>::allocate(__n, 0);
}
[[__gnu__::__always_inline__]]
constexpr void
deallocate(_Tp* __p, size_t __n)
{
#ifdef __cpp_lib_is_constant_evaluated
if (std::is_constant_evaluated())
{
::operator delete(__p);
return;
}
#endif
__allocator_base<_Tp>::deallocate(__p, __n);
}
#endif // C++20
friend _GLIBCXX20_CONSTEXPR bool
operator==(const allocator&, const allocator&) _GLIBCXX_NOTHROW
{ return true; }
#if __cpp_impl_three_way_comparison < 201907L
friend _GLIBCXX20_CONSTEXPR bool
operator!=(const allocator&, const allocator&) _GLIBCXX_NOTHROW
{ return false; }
#endif
// Inherit everything else.
};
template<typename _T1, typename _T2>
inline _GLIBCXX20_CONSTEXPR bool
operator==(const allocator<_T1>&, const allocator<_T2>&)
_GLIBCXX_NOTHROW
{ return true; }
#if __cpp_impl_three_way_comparison < 201907L
template<typename _T1, typename _T2>
inline _GLIBCXX20_CONSTEXPR bool
operator!=(const allocator<_T1>&, const allocator<_T2>&)
_GLIBCXX_NOTHROW
{ return false; }
#endif
// Invalid allocator<cv T> partial specializations.
// allocator_traits::rebind_alloc can be used to form a valid allocator type.
template<typename _Tp>
class allocator<const _Tp>
{
public:
typedef _Tp value_type;
template<typename _Up> allocator(const allocator<_Up>&) { }
};
template<typename _Tp>
class allocator<volatile _Tp>
{
public:
typedef _Tp value_type;
template<typename _Up> allocator(const allocator<_Up>&) { }
};
template<typename _Tp>
class allocator<const volatile _Tp>
{
public:
typedef _Tp value_type;
template<typename _Up> allocator(const allocator<_Up>&) { }
};
/// @} group allocator
// Inhibit implicit instantiations for required instantiations,
// which are defined via explicit instantiations elsewhere.
#if _GLIBCXX_EXTERN_TEMPLATE
extern template class allocator<char>;
extern template class allocator<wchar_t>;
#endif
// Undefine.
#undef __allocator_base
// To implement Option 3 of DR 431.
template<typename _Alloc, bool = __is_empty(_Alloc)>
struct __alloc_swap
{ static void _S_do_it(_Alloc&, _Alloc&) _GLIBCXX_NOEXCEPT { } };
template<typename _Alloc>
struct __alloc_swap<_Alloc, false>
{
static void
_S_do_it(_Alloc& __one, _Alloc& __two) _GLIBCXX_NOEXCEPT
{
// Precondition: swappable allocators.
if (__one != __two)
swap(__one, __two);
}
};
// Optimize for stateless allocators.
template<typename _Alloc, bool = __is_empty(_Alloc)>
struct __alloc_neq
{
static bool
_S_do_it(const _Alloc&, const _Alloc&)
{ return false; }
};
template<typename _Alloc>
struct __alloc_neq<_Alloc, false>
{
static bool
_S_do_it(const _Alloc& __one, const _Alloc& __two)
{ return __one != __two; }
};
#if __cplusplus >= 201103L
template<typename _Tp, bool
= __or_<is_copy_constructible<typename _Tp::value_type>,
is_nothrow_move_constructible<typename _Tp::value_type>>::value>
struct __shrink_to_fit_aux
{ static bool _S_do_it(_Tp&) noexcept { return false; } };
template<typename _Tp>
struct __shrink_to_fit_aux<_Tp, true>
{
static bool
_S_do_it(_Tp& __c) noexcept
{
#if __cpp_exceptions
try
{
_Tp(__make_move_if_noexcept_iterator(__c.begin()),
__make_move_if_noexcept_iterator(__c.end()),
__c.get_allocator()).swap(__c);
return true;
}
catch(...)
{ return false; }
#else
return false;
#endif
}
};
#endif
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif
memoryfwd.h
c++allocator.h
std::true_type
integral_constant< bool, true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:83
std::swap
void swap(any &__x, any &__y) noexcept
Exchange the states of two any objects.
Definition: any:428
std
ISO C++ entities toplevel namespace is std.
std::integral_constant
integral_constant
Definition: type_traits:66
std::allocator
The standard allocator, as per C++03 [20.4.1].
Definition: allocator.h:125
__gnu_cxx::new_allocator
An allocator that uses global new, as per C++03 [20.4.1].
Definition: new_allocator.h:56
type_traits