libstdc++
allocator.h
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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
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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.
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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 201505L
53
54namespace 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 /** std::allocator<void> specialization.
71 *
72 * @headerfile memory
73 */
74 template<>
76 {
77 public:
78 typedef void value_type;
79 typedef size_t size_type;
80 typedef ptrdiff_t difference_type;
81
82#if __cplusplus <= 201703L
83 // These were removed for C++20, allocator_traits does the right thing.
84 typedef void* pointer;
85 typedef const void* const_pointer;
86
87 template<typename _Tp1>
88 struct rebind
89 { typedef allocator<_Tp1> other; };
90#endif
91
92#if __cplusplus >= 201103L
93 // _GLIBCXX_RESOLVE_LIB_DEFECTS
94 // 2103. std::allocator propagate_on_container_move_assignment
96
97 using is_always_equal
98 _GLIBCXX20_DEPRECATED_SUGGEST("std::allocator_traits::is_always_equal")
99 = true_type;
100
101#if __cplusplus >= 202002L
102 // As noted above, these members are present for C++20 to provide the
103 // same API as the primary template, but still trivial as in pre-C++20.
104 allocator() = default;
105 ~allocator() = default;
106
107 template<typename _Up>
108 constexpr
109 allocator(const allocator<_Up>&) noexcept { }
110
111 // No allocate member because it's ill-formed by LWG 3307.
112 // No deallocate member because it would be undefined to call it
113 // with any pointer which wasn't obtained from allocate.
114#endif // C++20
115#endif // C++11
116 };
117
118 /**
119 * @brief The @a standard allocator, as per C++03 [20.4.1].
120 *
121 * See https://gcc.gnu.org/onlinedocs/libstdc++/manual/memory.html#std.util.memory.allocator
122 * for further details.
123 *
124 * @tparam _Tp Type of allocated object.
125 *
126 * @headerfile memory
127 */
128 template<typename _Tp>
129 class allocator : public __allocator_base<_Tp>
130 {
131 public:
132 typedef _Tp value_type;
133 typedef size_t size_type;
134 typedef ptrdiff_t difference_type;
135
136#if __cplusplus <= 201703L
137 // These were removed for C++20.
138 typedef _Tp* pointer;
139 typedef const _Tp* const_pointer;
140 typedef _Tp& reference;
141 typedef const _Tp& const_reference;
142
143 template<typename _Tp1>
144 struct rebind
145 { typedef allocator<_Tp1> other; };
146#endif
147
148#if __cplusplus >= 201103L
149 // _GLIBCXX_RESOLVE_LIB_DEFECTS
150 // 2103. std::allocator propagate_on_container_move_assignment
152
153 using is_always_equal
154 _GLIBCXX20_DEPRECATED_SUGGEST("std::allocator_traits::is_always_equal")
155 = true_type;
156#endif
157
158 // _GLIBCXX_RESOLVE_LIB_DEFECTS
159 // 3035. std::allocator's constructors should be constexpr
162
165 : __allocator_base<_Tp>(__a) { }
166
167#if __cplusplus >= 201103L
168 // Avoid implicit deprecation.
169 allocator& operator=(const allocator&) = default;
170#endif
171
172 template<typename _Tp1>
175
176#if __cpp_constexpr_dynamic_alloc
177 constexpr
178#endif
180
181#if __cplusplus > 201703L
182 [[nodiscard,__gnu__::__always_inline__]]
183 constexpr _Tp*
184 allocate(size_t __n)
185 {
186 if (std::__is_constant_evaluated())
187 {
188 if (__builtin_mul_overflow(__n, sizeof(_Tp), &__n))
189 std::__throw_bad_array_new_length();
190 return static_cast<_Tp*>(::operator new(__n));
191 }
192
193 return __allocator_base<_Tp>::allocate(__n, 0);
194 }
195
196 [[__gnu__::__always_inline__]]
197 constexpr void
198 deallocate(_Tp* __p, size_t __n)
199 {
200 if (std::__is_constant_evaluated())
201 {
202 ::operator delete(__p);
203 return;
204 }
206 }
207#endif // C++20
208
209 friend _GLIBCXX20_CONSTEXPR bool
210 operator==(const allocator&, const allocator&) _GLIBCXX_NOTHROW
211 { return true; }
212
213#if __cpp_impl_three_way_comparison < 201907L
214 friend _GLIBCXX20_CONSTEXPR bool
215 operator!=(const allocator&, const allocator&) _GLIBCXX_NOTHROW
216 { return false; }
217#endif
218
219 // Inherit everything else.
220 };
221
222 /** Equality comparison for std::allocator objects
223 *
224 * @return true, for all std::allocator objects.
225 * @relates std::allocator
226 */
227 template<typename _T1, typename _T2>
228 inline _GLIBCXX20_CONSTEXPR bool
231 { return true; }
232
233#if __cpp_impl_three_way_comparison < 201907L
234 template<typename _T1, typename _T2>
235 inline _GLIBCXX20_CONSTEXPR bool
236 operator!=(const allocator<_T1>&, const allocator<_T2>&)
238 { return false; }
239#endif
240
241 /// @cond undocumented
242
243 // Invalid allocator<cv T> partial specializations.
244 // allocator_traits::rebind_alloc can be used to form a valid allocator type.
245 template<typename _Tp>
246 class allocator<const _Tp>
247 {
248 public:
249 typedef _Tp value_type;
250 template<typename _Up> allocator(const allocator<_Up>&) { }
251 };
252
253 template<typename _Tp>
254 class allocator<volatile _Tp>
255 {
256 public:
257 typedef _Tp value_type;
258 template<typename _Up> allocator(const allocator<_Up>&) { }
259 };
260
261 template<typename _Tp>
262 class allocator<const volatile _Tp>
263 {
264 public:
265 typedef _Tp value_type;
266 template<typename _Up> allocator(const allocator<_Up>&) { }
267 };
268
269 /// @} group allocator
270
271 // Inhibit implicit instantiations for required instantiations,
272 // which are defined via explicit instantiations elsewhere.
273#if _GLIBCXX_EXTERN_TEMPLATE
274 extern template class allocator<char>;
275 extern template class allocator<wchar_t>;
276#endif
277
278 // Undefine.
279#undef __allocator_base
280
281 // To implement Option 3 of DR 431.
282 template<typename _Alloc, bool = __is_empty(_Alloc)>
283 struct __alloc_swap
284 { static void _S_do_it(_Alloc&, _Alloc&) _GLIBCXX_NOEXCEPT { } };
285
286 template<typename _Alloc>
287 struct __alloc_swap<_Alloc, false>
288 {
289 static void
290 _S_do_it(_Alloc& __one, _Alloc& __two) _GLIBCXX_NOEXCEPT
291 {
292 // Precondition: swappable allocators.
293 if (__one != __two)
294 swap(__one, __two);
295 }
296 };
297
298 // Optimize for stateless allocators.
299 template<typename _Alloc, bool = __is_empty(_Alloc)>
300 struct __alloc_neq
301 {
302 static bool
303 _S_do_it(const _Alloc&, const _Alloc&)
304 { return false; }
305 };
306
307 template<typename _Alloc>
308 struct __alloc_neq<_Alloc, false>
309 {
310 static bool
311 _S_do_it(const _Alloc& __one, const _Alloc& __two)
312 { return __one != __two; }
313 };
314
315#if __cplusplus >= 201103L
316 template<typename _Tp, bool
317 = __or_<is_copy_constructible<typename _Tp::value_type>,
318 is_nothrow_move_constructible<typename _Tp::value_type>>::value>
319 struct __shrink_to_fit_aux
320 { static bool _S_do_it(_Tp&) noexcept { return false; } };
321
322 template<typename _Tp>
323 struct __shrink_to_fit_aux<_Tp, true>
324 {
325 _GLIBCXX20_CONSTEXPR
326 static bool
327 _S_do_it(_Tp& __c) noexcept
328 {
329#if __cpp_exceptions
330 try
331 {
332 _Tp(__make_move_if_noexcept_iterator(__c.begin()),
333 __make_move_if_noexcept_iterator(__c.end()),
334 __c.get_allocator()).swap(__c);
335 return true;
336 }
337 catch(...)
338 { return false; }
339#else
340 return false;
341#endif
342 }
343 };
344#endif
345 /// @endcond
346
347_GLIBCXX_END_NAMESPACE_VERSION
348} // namespace std
349
350#endif
integral_constant< bool, true > true_type
The type used as a compile-time boolean with true value.
Definition type_traits:82
void swap(any &__x, any &__y) noexcept
Exchange the states of two any objects.
Definition any:429
constexpr bool operator==(const allocator< _T1 > &, const allocator< _T2 > &) noexcept
Definition allocator.h:229
ISO C++ entities toplevel namespace is std.
integral_constant
Definition type_traits:63
The standard allocator, as per C++03 [20.4.1].
Definition allocator.h:130