libstdc++
allocator.h
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1 // Allocators -*- C++ -*-
2 
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4 //
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16 // Under Section 7 of GPL version 3, you are granted additional
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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
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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 #pragma GCC diagnostic push
53 #pragma GCC diagnostic ignored "-Wc++11-extensions"
54 
55 namespace std _GLIBCXX_VISIBILITY(default)
56 {
57 _GLIBCXX_BEGIN_NAMESPACE_VERSION
58 
59  /**
60  * @addtogroup allocators
61  * @{
62  */
63 
64  // Since C++20 the primary template should be used for allocator<void>,
65  // but then it would have a non-trivial default ctor and dtor for C++20,
66  // but trivial for C++98-17, which would be an ABI incompatibility between
67  // different standard dialects. So C++20 still uses the allocator<void>
68  // explicit specialization, with the historical ABI properties, but with
69  // the same members that are present in the primary template.
70 
71  /** std::allocator<void> specialization.
72  *
73  * @headerfile memory
74  */
75  template<>
76  class allocator<void>
77  {
78  public:
79  typedef void value_type;
80  typedef size_t size_type;
81  typedef ptrdiff_t difference_type;
82 
83 #if __cplusplus <= 201703L
84  // These were removed for C++20, allocator_traits does the right thing.
85  typedef void* pointer;
86  typedef const void* const_pointer;
87 
88  template<typename _Tp1>
89  struct rebind
90  { typedef allocator<_Tp1> other; };
91 #endif
92 
93 #if __cplusplus >= 201103L
94  // _GLIBCXX_RESOLVE_LIB_DEFECTS
95  // 2103. std::allocator propagate_on_container_move_assignment
96  using propagate_on_container_move_assignment = true_type;
97 
98 #if __cplusplus <= 202302L
99  using is_always_equal
100  _GLIBCXX20_DEPRECATED_SUGGEST("std::allocator_traits::is_always_equal")
101  = true_type;
102 #endif
103 
104 #if __cplusplus >= 202002L
105  // As noted above, these members are present for C++20 to provide the
106  // same API as the primary template, but still trivial as in pre-C++20.
107  allocator() = default;
108  ~allocator() = default;
109 
110  template<typename _Up>
111  __attribute__((__always_inline__))
112  constexpr
113  allocator(const allocator<_Up>&) noexcept { }
114 
115  // No allocate member because it's ill-formed by LWG 3307.
116  // No deallocate member because it would be undefined to call it
117  // with any pointer which wasn't obtained from allocate.
118 #endif // C++20
119 #endif // C++11
120  };
121 
122  /**
123  * @brief The @a standard allocator, as per C++03 [20.4.1].
124  *
125  * See https://gcc.gnu.org/onlinedocs/libstdc++/manual/memory.html#std.util.memory.allocator
126  * for further details.
127  *
128  * @tparam _Tp Type of allocated object.
129  *
130  * @headerfile memory
131  */
132  template<typename _Tp>
133  class allocator : public __allocator_base<_Tp>
134  {
135  public:
136  typedef _Tp value_type;
137  typedef size_t size_type;
138  typedef ptrdiff_t difference_type;
139 
140 #if __cplusplus <= 201703L
141  // These were removed for C++20.
142  typedef _Tp* pointer;
143  typedef const _Tp* const_pointer;
144  typedef _Tp& reference;
145  typedef const _Tp& const_reference;
146 
147  template<typename _Tp1>
148  struct rebind
149  { typedef allocator<_Tp1> other; };
150 #endif
151 
152 #if __cplusplus >= 201103L
153  // _GLIBCXX_RESOLVE_LIB_DEFECTS
154  // 2103. std::allocator propagate_on_container_move_assignment
155  using propagate_on_container_move_assignment = true_type;
156 
157 #if __cplusplus <= 202302L
158  using is_always_equal
159  _GLIBCXX20_DEPRECATED_SUGGEST("std::allocator_traits::is_always_equal")
160  = true_type;
161 #endif
162 #endif
163 
164  // _GLIBCXX_RESOLVE_LIB_DEFECTS
165  // 3035. std::allocator's constructors should be constexpr
166  __attribute__((__always_inline__))
167  _GLIBCXX20_CONSTEXPR
168  allocator() _GLIBCXX_NOTHROW { }
169 
170  __attribute__((__always_inline__))
171  _GLIBCXX20_CONSTEXPR
172  allocator(const allocator& __a) _GLIBCXX_NOTHROW
173  : __allocator_base<_Tp>(__a) { }
174 
175 #if __cplusplus >= 201103L
176  // Avoid implicit deprecation.
177  allocator& operator=(const allocator&) = default;
178 #endif
179 
180  template<typename _Tp1>
181  __attribute__((__always_inline__))
182  _GLIBCXX20_CONSTEXPR
183  allocator(const allocator<_Tp1>&) _GLIBCXX_NOTHROW { }
184 
185  __attribute__((__always_inline__))
186 #if __cpp_constexpr_dynamic_alloc
187  constexpr
188 #endif
189  ~allocator() _GLIBCXX_NOTHROW { }
190 
191 #if __cplusplus > 201703L
192  [[nodiscard,__gnu__::__always_inline__]]
193  constexpr _Tp*
194  allocate(size_t __n)
195  {
196  if (std::__is_constant_evaluated())
197  {
198  if (__builtin_mul_overflow(__n, sizeof(_Tp), &__n))
199  std::__throw_bad_array_new_length();
200  return static_cast<_Tp*>(::operator new(__n));
201  }
202 
203  return __allocator_base<_Tp>::allocate(__n, 0);
204  }
205 
206  [[__gnu__::__always_inline__]]
207  constexpr void
208  deallocate(_Tp* __p, size_t __n)
209  {
210  if (std::__is_constant_evaluated())
211  {
212  ::operator delete(__p);
213  return;
214  }
216  }
217 #endif // C++20
218 
219  friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR
220  bool
221  operator==(const allocator&, const allocator&) _GLIBCXX_NOTHROW
222  { return true; }
223 
224 #if __cpp_impl_three_way_comparison < 201907L
225  friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR
226  bool
227  operator!=(const allocator&, const allocator&) _GLIBCXX_NOTHROW
228  { return false; }
229 #endif
230 
231  // Inherit everything else.
232  };
233 
234  /** Equality comparison for std::allocator objects
235  *
236  * @return true, for all std::allocator objects.
237  * @relates std::allocator
238  */
239  template<typename _T1, typename _T2>
240  __attribute__((__always_inline__))
241  inline _GLIBCXX20_CONSTEXPR bool
243  _GLIBCXX_NOTHROW
244  { return true; }
245 
246 #if __cpp_impl_three_way_comparison < 201907L
247  template<typename _T1, typename _T2>
248  __attribute__((__always_inline__))
249  inline _GLIBCXX20_CONSTEXPR bool
250  operator!=(const allocator<_T1>&, const allocator<_T2>&)
251  _GLIBCXX_NOTHROW
252  { return false; }
253 #endif
254 
255  /// @cond undocumented
256 
257  // Invalid allocator<cv T> partial specializations.
258  // allocator_traits::rebind_alloc can be used to form a valid allocator type.
259  template<typename _Tp>
260  class allocator<const _Tp>
261  {
262  public:
263  typedef _Tp value_type;
264  allocator() { }
265  template<typename _Up> allocator(const allocator<_Up>&) { }
266  };
267 
268  template<typename _Tp>
269  class allocator<volatile _Tp>
270  {
271  public:
272  typedef _Tp value_type;
273  allocator() { }
274  template<typename _Up> allocator(const allocator<_Up>&) { }
275  };
276 
277  template<typename _Tp>
278  class allocator<const volatile _Tp>
279  {
280  public:
281  typedef _Tp value_type;
282  allocator() { }
283  template<typename _Up> allocator(const allocator<_Up>&) { }
284  };
285  /// @endcond
286 
287  /// @} group allocator
288 
289  // Inhibit implicit instantiations for required instantiations,
290  // which are defined via explicit instantiations elsewhere.
291 #if _GLIBCXX_EXTERN_TEMPLATE
292  extern template class allocator<char>;
293  extern template class allocator<wchar_t>;
294 #endif
295 
296  // Undefine.
297 #undef __allocator_base
298 
299 _GLIBCXX_END_NAMESPACE_VERSION
300 } // namespace std
301 
302 #pragma GCC diagnostic pop
303 #endif
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:116
constexpr bool operator==(const allocator< _T1 > &, const allocator< _T2 > &) noexcept
Definition: allocator.h:242
ISO C++ entities toplevel namespace is std.
The standard allocator, as per C++03 [20.4.1].
Definition: allocator.h:134
An allocator that uses global new, as per C++03 [20.4.1].