libstdc++
allocator.h
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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
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10 
11 // This library is distributed in the hope that it will be useful,
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15 
16 // Under Section 7 of GPL version 3, you are granted additional
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18 // 3.1, as published by the Free Software Foundation.
19 
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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  }
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
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  allocator() { }
258  template<typename _Up> allocator(const allocator<_Up>&) { }
259  };
260 
261  template<typename _Tp>
262  class allocator<volatile _Tp>
263  {
264  public:
265  typedef _Tp value_type;
266  allocator() { }
267  template<typename _Up> allocator(const allocator<_Up>&) { }
268  };
269 
270  template<typename _Tp>
271  class allocator<const volatile _Tp>
272  {
273  public:
274  typedef _Tp value_type;
275  allocator() { }
276  template<typename _Up> allocator(const allocator<_Up>&) { }
277  };
278  /// @endcond
279 
280  /// @} group allocator
281 
282  // Inhibit implicit instantiations for required instantiations,
283  // which are defined via explicit instantiations elsewhere.
284 #if _GLIBCXX_EXTERN_TEMPLATE
285  extern template class allocator<char>;
286  extern template class allocator<wchar_t>;
287 #endif
288 
289  // Undefine.
290 #undef __allocator_base
291 
292 _GLIBCXX_END_NAMESPACE_VERSION
293 } // namespace std
294 
295 #endif
ISO C++ entities toplevel namespace is std.
An allocator that uses global new, as per C++03 [20.4.1].This is precisely the allocator defined in t...
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:111
The standard allocator, as per C++03 [20.4.1].
Definition: allocator.h:128
constexpr bool operator==(const allocator< _T1 > &, const allocator< _T2 > &) noexcept
Definition: allocator.h:235