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
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 /// 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
92 using propagate_on_container_move_assignment = true_type;
93
94 using is_always_equal
95 _GLIBCXX20_DEPRECATED_SUGGEST("std::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
146 using propagate_on_container_move_assignment = true_type;
147
148 using is_always_equal
149 _GLIBCXX20_DEPRECATED_SUGGEST("std::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
199 __allocator_base<_Tp>::deallocate(__p, __n);
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
336

source code of include/c++/11/bits/allocator.h