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
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10 
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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 #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
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
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 #ifdef __cpp_lib_is_constant_evaluated
182  if (std::is_constant_evaluated())
183  return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp)));
184 #endif
185  return __allocator_base<_Tp>::allocate(__n, 0);
186  }
187 
188  [[__gnu__::__always_inline__]]
189  constexpr void
190  deallocate(_Tp* __p, size_t __n)
191  {
192 #ifdef __cpp_lib_is_constant_evaluated
193  if (std::is_constant_evaluated())
194  {
195  ::operator delete(__p);
196  return;
197  }
198 #endif
200  }
201 #endif // C++20
202 
203  friend _GLIBCXX20_CONSTEXPR bool
204  operator==(const allocator&, const allocator&) _GLIBCXX_NOTHROW
205  { return true; }
206 
207 #if __cpp_impl_three_way_comparison < 201907L
208  friend _GLIBCXX20_CONSTEXPR bool
209  operator!=(const allocator&, const allocator&) _GLIBCXX_NOTHROW
210  { return false; }
211 #endif
212 
213  // Inherit everything else.
214  };
215 
216  template<typename _T1, typename _T2>
217  inline _GLIBCXX20_CONSTEXPR bool
218  operator==(const allocator<_T1>&, const allocator<_T2>&)
219  _GLIBCXX_NOTHROW
220  { return true; }
221 
222 #if __cpp_impl_three_way_comparison < 201907L
223  template<typename _T1, typename _T2>
224  inline _GLIBCXX20_CONSTEXPR bool
225  operator!=(const allocator<_T1>&, const allocator<_T2>&)
226  _GLIBCXX_NOTHROW
227  { return false; }
228 #endif
229 
230  // Invalid allocator<cv T> partial specializations.
231  // allocator_traits::rebind_alloc can be used to form a valid allocator type.
232  template<typename _Tp>
233  class allocator<const _Tp>
234  {
235  public:
236  typedef _Tp value_type;
237  template<typename _Up> allocator(const allocator<_Up>&) { }
238  };
239 
240  template<typename _Tp>
241  class allocator<volatile _Tp>
242  {
243  public:
244  typedef _Tp value_type;
245  template<typename _Up> allocator(const allocator<_Up>&) { }
246  };
247 
248  template<typename _Tp>
249  class allocator<const volatile _Tp>
250  {
251  public:
252  typedef _Tp value_type;
253  template<typename _Up> allocator(const allocator<_Up>&) { }
254  };
255 
256  /// @} group allocator
257 
258  // Inhibit implicit instantiations for required instantiations,
259  // which are defined via explicit instantiations elsewhere.
260 #if _GLIBCXX_EXTERN_TEMPLATE
261  extern template class allocator<char>;
262  extern template class allocator<wchar_t>;
263 #endif
264 
265  // Undefine.
266 #undef __allocator_base
267 
268  // To implement Option 3 of DR 431.
269  template<typename _Alloc, bool = __is_empty(_Alloc)>
270  struct __alloc_swap
271  { static void _S_do_it(_Alloc&, _Alloc&) _GLIBCXX_NOEXCEPT { } };
272 
273  template<typename _Alloc>
274  struct __alloc_swap<_Alloc, false>
275  {
276  static void
277  _S_do_it(_Alloc& __one, _Alloc& __two) _GLIBCXX_NOEXCEPT
278  {
279  // Precondition: swappable allocators.
280  if (__one != __two)
281  swap(__one, __two);
282  }
283  };
284 
285  // Optimize for stateless allocators.
286  template<typename _Alloc, bool = __is_empty(_Alloc)>
287  struct __alloc_neq
288  {
289  static bool
290  _S_do_it(const _Alloc&, const _Alloc&)
291  { return false; }
292  };
293 
294  template<typename _Alloc>
295  struct __alloc_neq<_Alloc, false>
296  {
297  static bool
298  _S_do_it(const _Alloc& __one, const _Alloc& __two)
299  { return __one != __two; }
300  };
301 
302 #if __cplusplus >= 201103L
303  template<typename _Tp, bool
304  = __or_<is_copy_constructible<typename _Tp::value_type>,
305  is_nothrow_move_constructible<typename _Tp::value_type>>::value>
306  struct __shrink_to_fit_aux
307  { static bool _S_do_it(_Tp&) noexcept { return false; } };
308 
309  template<typename _Tp>
310  struct __shrink_to_fit_aux<_Tp, true>
311  {
312  static bool
313  _S_do_it(_Tp& __c) noexcept
314  {
315 #if __cpp_exceptions
316  try
317  {
318  _Tp(__make_move_if_noexcept_iterator(__c.begin()),
319  __make_move_if_noexcept_iterator(__c.end()),
320  __c.get_allocator()).swap(__c);
321  return true;
322  }
323  catch(...)
324  { return false; }
325 #else
326  return false;
327 #endif
328  }
329  };
330 #endif
331 
332 _GLIBCXX_END_NAMESPACE_VERSION
333 } // namespace std
334 
335 #endif
integral_constant
Definition: type_traits:65
The standard allocator, as per C++03 [20.4.1].
Definition: allocator.h:124
integral_constant< bool, true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:83
An allocator that uses global new, as per C++03 [20.4.1].This is precisely the allocator defined in t...
Definition: new_allocator.h:55
ISO C++ entities toplevel namespace is std.