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

   1 // Allocators -*- C++ -*-
   2
   3 // Copyright (C) 2001-2022 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 #define __cpp_lib_incomplete_container_elements 201505
  53
  54 namespace std _GLIBCXX_VISIBILITY(default)
  55 {
  56 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  57
  58   /**
  59    *  @addtogroup allocators
  60    *  @{
  61    */
  62
  63   // Since C++20 the primary template should be used for allocator<void>,
  64   // but then it would have a non-trivial default ctor and dtor for C++20,
  65   // but trivial for C++98-17, which would be an ABI incompatibiliy between
  66   // different standard dialects. So C++20 still uses the allocator<void>
  67   // explicit specialization, with the historical ABI properties, but with
  68   // the same members that are present in the primary template.
  69
  70   /// allocator<void> specialization.
  71   template<>
  72     class allocator<void>
  73     {
  74     public:
  75       typedef void        value_type;
  76       typedef size_t      size_type;
  77       typedef ptrdiff_t   difference_type;
  78
  79 #if __cplusplus <= 201703L
  80       // These were removed for C++20, allocator_traits does the right thing.
  81       typedef void*       pointer;
  82       typedef const void* const_pointer;
  83
  84       template<typename _Tp1>
  85         struct rebind
  86         { typedef allocator<_Tp1> other; };
  87 #endif
  88
  89 #if __cplusplus >= 201103L
  90       // _GLIBCXX_RESOLVE_LIB_DEFECTS
  91       // 2103. std::allocator propagate_on_container_move_assignment
  92       using propagate_on_container_move_assignment = true_type;
  93
  94       using is_always_equal
  95         _GLIBCXX20_DEPRECATED_SUGGEST("allocator_traits::is_always_equal")
  96         = true_type;
  97
  98 #if __cplusplus >= 202002L
  99       // As noted above, these members are present for C++20 to provide the
 100       // same API as the primary template, but still trivial as in pre-C++20.
 101       allocator() = default;
 102       ~allocator() = default;
 103
 104       template<typename _Up>
 105         constexpr
 106         allocator(const allocator<_Up>&) noexcept { }
 107
 108       // No allocate member because it's ill-formed by LWG 3307.
 109       // No deallocate member because it would be undefined to call it
 110       // with any pointer which wasn't obtained from allocate.
 111 #endif // C++20
 112 #endif // C++11
 113     };
 114
 115   /**
 116    * @brief  The @a standard allocator, as per C++03 [20.4.1].
 117    *
 118    *  See https://gcc.gnu.org/onlinedocs/libstdc++/manual/memory.html#std.util.memory.allocator
 119    *  for further details.
 120    *
 121    *  @tparam  _Tp  Type of allocated object.
 122    */
 123   template<typename _Tp>
 124     class allocator : public __allocator_base<_Tp>
 125     {
 126     public:
 127       typedef _Tp        value_type;
 128       typedef size_t     size_type;
 129       typedef ptrdiff_t  difference_type;
 130
 131 #if __cplusplus <= 201703L
 132       // These were removed for C++20.
 133       typedef _Tp*       pointer;
 134       typedef const _Tp* const_pointer;
 135       typedef _Tp&       reference;
 136       typedef const _Tp& const_reference;
 137
 138       template<typename _Tp1>
 139         struct rebind
 140         { typedef allocator<_Tp1> other; };
 141 #endif
 142
 143 #if __cplusplus >= 201103L
 144       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 145       // 2103. std::allocator propagate_on_container_move_assignment
 146       using propagate_on_container_move_assignment = true_type;
 147
 148       using is_always_equal
 149         _GLIBCXX20_DEPRECATED_SUGGEST("allocator_traits::is_always_equal")
 150         = true_type;
 151 #endif
 152
 153       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 154       // 3035. std::allocator's constructors should be constexpr
 155       _GLIBCXX20_CONSTEXPR
 156       allocator() _GLIBCXX_NOTHROW { }
 157
 158       _GLIBCXX20_CONSTEXPR
 159       allocator(const allocator& __a) _GLIBCXX_NOTHROW
 160       : __allocator_base<_Tp>(__a) { }
 161
 162 #if __cplusplus >= 201103L
 163       // Avoid implicit deprecation.
 164       allocator& operator=(const allocator&) = default;
 165 #endif
 166
 167       template<typename _Tp1>
 168         _GLIBCXX20_CONSTEXPR
 169         allocator(const allocator<_Tp1>&) _GLIBCXX_NOTHROW { }
 170
 171 #if __cpp_constexpr_dynamic_alloc
 172       constexpr
 173 #endif
 174       ~allocator() _GLIBCXX_NOTHROW { }
 175
 176 #if __cplusplus > 201703L
 177       [[nodiscard,__gnu__::__always_inline__]]
 178       constexpr _Tp*
 179       allocate(size_t __n)
 180       {
 181         if (std::__is_constant_evaluated())
 182           return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp)));
 183         return __allocator_base<_Tp>::allocate(__n, 0);
 184       }
 185
 186       [[__gnu__::__always_inline__]]
 187       constexpr void
 188       deallocate(_Tp* __p, size_t __n)
 189       {
 190         if (std::__is_constant_evaluated())
 191           {
 192             ::operator delete(__p);
 193             return;
 194           }
 195         __allocator_base<_Tp>::deallocate(__p, __n);
 196       }
 197 #endif // C++20
 198
 199       friend _GLIBCXX20_CONSTEXPR bool
 200       operator==(const allocator&, const allocator&) _GLIBCXX_NOTHROW
 201       { return true; }
 202
 203 #if __cpp_impl_three_way_comparison < 201907L
 204       friend _GLIBCXX20_CONSTEXPR bool
 205       operator!=(const allocator&, const allocator&) _GLIBCXX_NOTHROW
 206       { return false; }
 207 #endif
 208
 209       // Inherit everything else.
 210     };
 211
 212   template<typename _T1, typename _T2>
 213     inline _GLIBCXX20_CONSTEXPR bool
 214     operator==(const allocator<_T1>&, const allocator<_T2>&)
 215     _GLIBCXX_NOTHROW
 216     { return true; }
 217
 218 #if __cpp_impl_three_way_comparison < 201907L
 219   template<typename _T1, typename _T2>
 220     inline _GLIBCXX20_CONSTEXPR bool
 221     operator!=(const allocator<_T1>&, const allocator<_T2>&)
 222     _GLIBCXX_NOTHROW
 223     { return false; }
 224 #endif
 225
 226   // Invalid allocator<cv T> partial specializations.
 227   // allocator_traits::rebind_alloc can be used to form a valid allocator type.
 228   template<typename _Tp>
 229     class allocator<const _Tp>
 230     {
 231     public:
 232       typedef _Tp value_type;
 233       template<typename _Up> allocator(const allocator<_Up>&) { }
 234     };
 235
 236   template<typename _Tp>
 237     class allocator<volatile _Tp>
 238     {
 239     public:
 240       typedef _Tp value_type;
 241       template<typename _Up> allocator(const allocator<_Up>&) { }
 242     };
 243
 244   template<typename _Tp>
 245     class allocator<const volatile _Tp>
 246     {
 247     public:
 248       typedef _Tp value_type;
 249       template<typename _Up> allocator(const allocator<_Up>&) { }
 250     };
 251
 252   /// @} group allocator
 253
 254   // Inhibit implicit instantiations for required instantiations,
 255   // which are defined via explicit instantiations elsewhere.
 256 #if _GLIBCXX_EXTERN_TEMPLATE
 257   extern template class allocator<char>;
 258   extern template class allocator<wchar_t>;
 259 #endif
 260
 261   // Undefine.
 262 #undef __allocator_base
 263
 264   // To implement Option 3 of DR 431.
 265   template<typename _Alloc, bool = __is_empty(_Alloc)>
 266     struct __alloc_swap
 267     { static void _S_do_it(_Alloc&, _Alloc&) _GLIBCXX_NOEXCEPT { } };
 268
 269   template<typename _Alloc>
 270     struct __alloc_swap<_Alloc, false>
 271     {
 272       static void
 273       _S_do_it(_Alloc& __one, _Alloc& __two) _GLIBCXX_NOEXCEPT
 274       {
 275         // Precondition: swappable allocators.
 276         if (__one != __two)
 277           swap(__one, __two);
 278       }
 279     };
 280
 281   // Optimize for stateless allocators.
 282   template<typename _Alloc, bool = __is_empty(_Alloc)>
 283     struct __alloc_neq
 284     {
 285       static bool
 286       _S_do_it(const _Alloc&, const _Alloc&)
 287       { return false; }
 288     };
 289
 290   template<typename _Alloc>
 291     struct __alloc_neq<_Alloc, false>
 292     {
 293       static bool
 294       _S_do_it(const _Alloc& __one, const _Alloc& __two)
 295       { return __one != __two; }
 296     };
 297
 298 #if __cplusplus >= 201103L
 299   template<typename _Tp, bool
 300     = __or_<is_copy_constructible<typename _Tp::value_type>,
 301             is_nothrow_move_constructible<typename _Tp::value_type>>::value>
 302     struct __shrink_to_fit_aux
 303     { static bool _S_do_it(_Tp&) noexcept { return false; } };
 304
 305   template<typename _Tp>
 306     struct __shrink_to_fit_aux<_Tp, true>
 307     {
 308       _GLIBCXX20_CONSTEXPR
 309       static bool
 310       _S_do_it(_Tp& __c) noexcept
 311       {
 312 #if __cpp_exceptions
 313         try
 314           {
 315             _Tp(__make_move_if_noexcept_iterator(__c.begin()),
 316                 __make_move_if_noexcept_iterator(__c.end()),
 317                 __c.get_allocator()).swap(__c);
 318             return true;
 319           }
 320         catch(...)
 321           { return false; }
 322 #else
 323         return false;
 324 #endif
 325       }
 326     };
 327 #endif
 328
 329 _GLIBCXX_END_NAMESPACE_VERSION
 330 } // namespace std
 331
 332 #endif