libstdc++
allocator.h
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1 // Allocators -*- C++ -*-
2 
3 // Copyright (C) 2001-2021 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  /// allocator<void> specialization.
64  template<>
65  class allocator<void>
66  {
67  public:
68  typedef void value_type;
69  typedef size_t size_type;
70  typedef ptrdiff_t difference_type;
71 #if __cplusplus <= 201703L
72  typedef void* pointer;
73  typedef const void* const_pointer;
74 
75  template<typename _Tp1>
76  struct rebind
77  { typedef allocator<_Tp1> other; };
78 #else
79  allocator() = default;
80 
81  template<typename _Up>
82  constexpr
83  allocator(const allocator<_Up>&) { }
84 #endif // ! C++20
85 
86 #if __cplusplus >= 201103L && __cplusplus <= 201703L
87  // _GLIBCXX_RESOLVE_LIB_DEFECTS
88  // 2103. std::allocator propagate_on_container_move_assignment
90 
91  typedef true_type is_always_equal;
92 
93  template<typename _Up, typename... _Args>
94  void
95  construct(_Up* __p, _Args&&... __args)
97  { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
98 
99  template<typename _Up>
100  void
101  destroy(_Up* __p)
103  { __p->~_Up(); }
104 #endif // C++11 to C++17
105  };
106 
107  /**
108  * @brief The @a standard allocator, as per [20.4].
109  *
110  * See https://gcc.gnu.org/onlinedocs/libstdc++/manual/memory.html#std.util.memory.allocator
111  * for further details.
112  *
113  * @tparam _Tp Type of allocated object.
114  */
115  template<typename _Tp>
116  class allocator : public __allocator_base<_Tp>
117  {
118  public:
119  typedef _Tp value_type;
120  typedef size_t size_type;
121  typedef ptrdiff_t difference_type;
122 #if __cplusplus <= 201703L
123  typedef _Tp* pointer;
124  typedef const _Tp* const_pointer;
125  typedef _Tp& reference;
126  typedef const _Tp& const_reference;
127 
128  template<typename _Tp1>
129  struct rebind
130  { typedef allocator<_Tp1> other; };
131 #endif
132 
133 #if __cplusplus >= 201103L
134  // _GLIBCXX_RESOLVE_LIB_DEFECTS
135  // 2103. std::allocator propagate_on_container_move_assignment
137 
138  typedef true_type is_always_equal;
139 #endif
140 
141  // _GLIBCXX_RESOLVE_LIB_DEFECTS
142  // 3035. std::allocator's constructors should be constexpr
143  _GLIBCXX20_CONSTEXPR
144  allocator() _GLIBCXX_NOTHROW { }
145 
146  _GLIBCXX20_CONSTEXPR
147  allocator(const allocator& __a) _GLIBCXX_NOTHROW
148  : __allocator_base<_Tp>(__a) { }
149 
150 #if __cplusplus >= 201103L
151  // Avoid implicit deprecation.
152  allocator& operator=(const allocator&) = default;
153 #endif
154 
155  template<typename _Tp1>
156  _GLIBCXX20_CONSTEXPR
157  allocator(const allocator<_Tp1>&) _GLIBCXX_NOTHROW { }
158 
159 #if __cpp_constexpr_dynamic_alloc
160  constexpr
161 #endif
162  ~allocator() _GLIBCXX_NOTHROW { }
163 
164 #if __cplusplus > 201703L
165  [[nodiscard,__gnu__::__always_inline__]]
166  constexpr _Tp*
167  allocate(size_t __n)
168  {
169 #ifdef __cpp_lib_is_constant_evaluated
170  if (std::is_constant_evaluated())
171  return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp)));
172 #endif
173  return __allocator_base<_Tp>::allocate(__n, 0);
174  }
175 
176  [[__gnu__::__always_inline__]]
177  constexpr void
178  deallocate(_Tp* __p, size_t __n)
179  {
180 #ifdef __cpp_lib_is_constant_evaluated
181  if (std::is_constant_evaluated())
182  {
183  ::operator delete(__p);
184  return;
185  }
186 #endif
188  }
189 #endif // C++20
190 
191  friend _GLIBCXX20_CONSTEXPR bool
192  operator==(const allocator&, const allocator&) _GLIBCXX_NOTHROW
193  { return true; }
194 
195 #if __cpp_impl_three_way_comparison < 201907L
196  friend _GLIBCXX20_CONSTEXPR bool
197  operator!=(const allocator&, const allocator&) _GLIBCXX_NOTHROW
198  { return false; }
199 #endif
200 
201  // Inherit everything else.
202  };
203 
204  template<typename _T1, typename _T2>
205  inline _GLIBCXX20_CONSTEXPR bool
206  operator==(const allocator<_T1>&, const allocator<_T2>&)
207  _GLIBCXX_NOTHROW
208  { return true; }
209 
210 #if __cpp_impl_three_way_comparison < 201907L
211  template<typename _T1, typename _T2>
212  inline _GLIBCXX20_CONSTEXPR bool
213  operator!=(const allocator<_T1>&, const allocator<_T2>&)
214  _GLIBCXX_NOTHROW
215  { return false; }
216 #endif
217 
218  // Invalid allocator<cv T> partial specializations.
219  // allocator_traits::rebind_alloc can be used to form a valid allocator type.
220  template<typename _Tp>
221  class allocator<const _Tp>
222  {
223  public:
224  typedef _Tp value_type;
225  template<typename _Up> allocator(const allocator<_Up>&) { }
226  };
227 
228  template<typename _Tp>
229  class allocator<volatile _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<const volatile _Tp>
238  {
239  public:
240  typedef _Tp value_type;
241  template<typename _Up> allocator(const allocator<_Up>&) { }
242  };
243 
244  /// @} group allocator
245 
246  // Inhibit implicit instantiations for required instantiations,
247  // which are defined via explicit instantiations elsewhere.
248 #if _GLIBCXX_EXTERN_TEMPLATE
249  extern template class allocator<char>;
250  extern template class allocator<wchar_t>;
251 #endif
252 
253  // Undefine.
254 #undef __allocator_base
255 
256  // To implement Option 3 of DR 431.
257  template<typename _Alloc, bool = __is_empty(_Alloc)>
258  struct __alloc_swap
259  { static void _S_do_it(_Alloc&, _Alloc&) _GLIBCXX_NOEXCEPT { } };
260 
261  template<typename _Alloc>
262  struct __alloc_swap<_Alloc, false>
263  {
264  static void
265  _S_do_it(_Alloc& __one, _Alloc& __two) _GLIBCXX_NOEXCEPT
266  {
267  // Precondition: swappable allocators.
268  if (__one != __two)
269  swap(__one, __two);
270  }
271  };
272 
273  // Optimize for stateless allocators.
274  template<typename _Alloc, bool = __is_empty(_Alloc)>
275  struct __alloc_neq
276  {
277  static bool
278  _S_do_it(const _Alloc&, const _Alloc&)
279  { return false; }
280  };
281 
282  template<typename _Alloc>
283  struct __alloc_neq<_Alloc, false>
284  {
285  static bool
286  _S_do_it(const _Alloc& __one, const _Alloc& __two)
287  { return __one != __two; }
288  };
289 
290 #if __cplusplus >= 201103L
291  template<typename _Tp, bool
292  = __or_<is_copy_constructible<typename _Tp::value_type>,
293  is_nothrow_move_constructible<typename _Tp::value_type>>::value>
294  struct __shrink_to_fit_aux
295  { static bool _S_do_it(_Tp&) noexcept { return false; } };
296 
297  template<typename _Tp>
298  struct __shrink_to_fit_aux<_Tp, true>
299  {
300  static bool
301  _S_do_it(_Tp& __c) noexcept
302  {
303 #if __cpp_exceptions
304  try
305  {
306  _Tp(__make_move_if_noexcept_iterator(__c.begin()),
307  __make_move_if_noexcept_iterator(__c.end()),
308  __c.get_allocator()).swap(__c);
309  return true;
310  }
311  catch(...)
312  { return false; }
313 #else
314  return false;
315 #endif
316  }
317  };
318 #endif
319 
320 _GLIBCXX_END_NAMESPACE_VERSION
321 } // namespace std
322 
323 #endif
void swap(any &__x, any &__y) noexcept
Exchange the states of two any objects.
Definition: any:412
ISO C++ entities toplevel namespace is std.
integral_constant
Definition: type_traits:58
is_nothrow_destructible
Definition: type_traits:899
is_nothrow_constructible
Definition: type_traits:977
The standard allocator, as per [20.4].
Definition: allocator.h:117
An allocator that uses global new, as per [20.4].
Definition: new_allocator.h:56