libstdc++-v3/include/bits/allocator.h

   1 // Allocators -*- C++ -*-
   2
   3 // Copyright (C) 2001-2024 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 /*
  26  * Copyright (c) 1996-1997
  27  * Silicon Graphics Computer Systems, Inc.
  28  *
  29  * Permission to use, copy, modify, distribute and sell this software
  30  * and its documentation for any purpose is hereby granted without fee,
  31  * provided that the above copyright notice appear in all copies and
  32  * that both that copyright notice and this permission notice appear
  33  * in supporting documentation.  Silicon Graphics makes no
  34  * representations about the suitability of this software for any
  35  * purpose.  It is provided "as is" without express or implied warranty.
  36  */
  37
  38 /** @file bits/allocator.h
  39  *  This is an internal header file, included by other library headers.
  40  *  Do not attempt to use it directly. @headername{memory}
  41  */
  42
  43 #ifndef _ALLOCATOR_H
  44 #define _ALLOCATOR_H 1
  45
  46 #include <bits/c++allocator.h> // Define the base class to std::allocator.
  47 #include <bits/memoryfwd.h>
  48 #if __cplusplus >= 201103L
  49 #include <type_traits>
  50 #endif
  51
  52 namespace std _GLIBCXX_VISIBILITY(default)
  53 {
  54 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  55
  56   /**
  57    *  @addtogroup allocators
  58    *  @{
  59    */
  60
  61   // Since C++20 the primary template should be used for allocator<void>,
  62   // but then it would have a non-trivial default ctor and dtor for C++20,
  63   // but trivial for C++98-17, which would be an ABI incompatibility between
  64   // different standard dialects. So C++20 still uses the allocator<void>
  65   // explicit specialization, with the historical ABI properties, but with
  66   // the same members that are present in the primary template.
  67
  68   /** std::allocator<void> specialization.
  69    *
  70    * @headerfile memory
  71    */
  72   template<>
  73     class allocator<void>
  74     {
  75     public:
  76       typedef void        value_type;
  77       typedef size_t      size_type;
  78       typedef ptrdiff_t   difference_type;
  79
  80 #if __cplusplus <= 201703L
  81       // These were removed for C++20, allocator_traits does the right thing.
  82       typedef void*       pointer;
  83       typedef const void* const_pointer;
  84
  85       template<typename _Tp1>
  86         struct rebind
  87         { typedef allocator<_Tp1> other; };
  88 #endif
  89
  90 #if __cplusplus >= 201103L
  91       // _GLIBCXX_RESOLVE_LIB_DEFECTS
  92       // 2103. std::allocator propagate_on_container_move_assignment
  93       using propagate_on_container_move_assignment = true_type;
  94
  95       using is_always_equal
  96         _GLIBCXX20_DEPRECATED_SUGGEST("std::allocator_traits::is_always_equal")
  97         = true_type;
  98
  99 #if __cplusplus >= 202002L
 100       // As noted above, these members are present for C++20 to provide the
 101       // same API as the primary template, but still trivial as in pre-C++20.
 102       allocator() = default;
 103       ~allocator() = default;
 104
 105       template<typename _Up>
 106         __attribute__((__always_inline__))
 107         constexpr
 108         allocator(const allocator<_Up>&) noexcept { }
 109
 110       // No allocate member because it's ill-formed by LWG 3307.
 111       // No deallocate member because it would be undefined to call it
 112       // with any pointer which wasn't obtained from allocate.
 113 #endif // C++20
 114 #endif // C++11
 115     };
 116
 117   /**
 118    * @brief  The @a standard allocator, as per C++03 [20.4.1].
 119    *
 120    *  See https://gcc.gnu.org/onlinedocs/libstdc++/manual/memory.html#std.util.memory.allocator
 121    *  for further details.
 122    *
 123    *  @tparam  _Tp  Type of allocated object.
 124    *
 125    *  @headerfile memory
 126    */
 127   template<typename _Tp>
 128     class allocator : public __allocator_base<_Tp>
 129     {
 130     public:
 131       typedef _Tp        value_type;
 132       typedef size_t     size_type;
 133       typedef ptrdiff_t  difference_type;
 134
 135 #if __cplusplus <= 201703L
 136       // These were removed for C++20.
 137       typedef _Tp*       pointer;
 138       typedef const _Tp* const_pointer;
 139       typedef _Tp&       reference;
 140       typedef const _Tp& const_reference;
 141
 142       template<typename _Tp1>
 143         struct rebind
 144         { typedef allocator<_Tp1> other; };
 145 #endif
 146
 147 #if __cplusplus >= 201103L
 148       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 149       // 2103. std::allocator propagate_on_container_move_assignment
 150       using propagate_on_container_move_assignment = true_type;
 151
 152       using is_always_equal
 153         _GLIBCXX20_DEPRECATED_SUGGEST("std::allocator_traits::is_always_equal")
 154         = true_type;
 155 #endif
 156
 157       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 158       // 3035. std::allocator's constructors should be constexpr
 159       __attribute__((__always_inline__))
 160       _GLIBCXX20_CONSTEXPR
 161       allocator() _GLIBCXX_NOTHROW { }
 162
 163       __attribute__((__always_inline__))
 164       _GLIBCXX20_CONSTEXPR
 165       allocator(const allocator& __a) _GLIBCXX_NOTHROW
 166       : __allocator_base<_Tp>(__a) { }
 167
 168 #if __cplusplus >= 201103L
 169       // Avoid implicit deprecation.
 170       allocator& operator=(const allocator&) = default;
 171 #endif
 172
 173       template<typename _Tp1>
 174         __attribute__((__always_inline__))
 175         _GLIBCXX20_CONSTEXPR
 176         allocator(const allocator<_Tp1>&) _GLIBCXX_NOTHROW { }
 177
 178       __attribute__((__always_inline__))
 179 #if __cpp_constexpr_dynamic_alloc
 180       constexpr
 181 #endif
 182       ~allocator() _GLIBCXX_NOTHROW { }
 183
 184 #if __cplusplus > 201703L
 185       [[nodiscard,__gnu__::__always_inline__]]
 186       constexpr _Tp*
 187       allocate(size_t __n)
 188       {
 189         if (std::__is_constant_evaluated())
 190           {
 191             if (__builtin_mul_overflow(__n, sizeof(_Tp), &__n))
 192               std::__throw_bad_array_new_length();
 193             return static_cast<_Tp*>(::operator new(__n));
 194           }
 195
 196         return __allocator_base<_Tp>::allocate(__n, 0);
 197       }
 198
 199       [[__gnu__::__always_inline__]]
 200       constexpr void
 201       deallocate(_Tp* __p, size_t __n)
 202       {
 203         if (std::__is_constant_evaluated())
 204           {
 205             ::operator delete(__p);
 206             return;
 207           }
 208         __allocator_base<_Tp>::deallocate(__p, __n);
 209       }
 210 #endif // C++20
 211
 212       friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR
 213       bool
 214       operator==(const allocator&, const allocator&) _GLIBCXX_NOTHROW
 215       { return true; }
 216
 217 #if __cpp_impl_three_way_comparison < 201907L
 218       friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR
 219       bool
 220       operator!=(const allocator&, const allocator&) _GLIBCXX_NOTHROW
 221       { return false; }
 222 #endif
 223
 224       // Inherit everything else.
 225     };
 226
 227   /** Equality comparison for std::allocator objects
 228    *
 229    * @return true, for all std::allocator objects.
 230    * @relates std::allocator
 231    */
 232   template<typename _T1, typename _T2>
 233     __attribute__((__always_inline__))
 234     inline _GLIBCXX20_CONSTEXPR bool
 235     operator==(const allocator<_T1>&, const allocator<_T2>&)
 236     _GLIBCXX_NOTHROW
 237     { return true; }
 238
 239 #if __cpp_impl_three_way_comparison < 201907L
 240   template<typename _T1, typename _T2>
 241     __attribute__((__always_inline__))
 242     inline _GLIBCXX20_CONSTEXPR bool
 243     operator!=(const allocator<_T1>&, const allocator<_T2>&)
 244     _GLIBCXX_NOTHROW
 245     { return false; }
 246 #endif
 247
 248   /// @cond undocumented
 249
 250   // Invalid allocator<cv T> partial specializations.
 251   // allocator_traits::rebind_alloc can be used to form a valid allocator type.
 252   template<typename _Tp>
 253     class allocator<const _Tp>
 254     {
 255     public:
 256       typedef _Tp value_type;
 257       template<typename _Up> allocator(const allocator<_Up>&) { }
 258     };
 259
 260   template<typename _Tp>
 261     class allocator<volatile _Tp>
 262     {
 263     public:
 264       typedef _Tp value_type;
 265       template<typename _Up> allocator(const allocator<_Up>&) { }
 266     };
 267
 268   template<typename _Tp>
 269     class allocator<const volatile _Tp>
 270     {
 271     public:
 272       typedef _Tp value_type;
 273       template<typename _Up> allocator(const allocator<_Up>&) { }
 274     };
 275   /// @endcond
 276
 277   /// @} group allocator
 278
 279   // Inhibit implicit instantiations for required instantiations,
 280   // which are defined via explicit instantiations elsewhere.
 281 #if _GLIBCXX_EXTERN_TEMPLATE
 282   extern template class allocator<char>;
 283   extern template class allocator<wchar_t>;
 284 #endif
 285
 286   // Undefine.
 287 #undef __allocator_base
 288
 289 _GLIBCXX_END_NAMESPACE_VERSION
 290 } // namespace std
 291
 292 #endif