libstdc++
bits/new_allocator.h
Go to the documentation of this file.
1 // Allocator that wraps operator new -*- C++ -*-
2 
3 // Copyright (C) 2001-2023 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 /** @file bits/new_allocator.h
26  * This is an internal header file, included by other library headers.
27  * Do not attempt to use it directly. @headername{memory}
28  */
29 
30 #ifndef _STD_NEW_ALLOCATOR_H
31 #define _STD_NEW_ALLOCATOR_H 1
32 
33 #include <bits/c++config.h>
34 #include <new>
35 #include <bits/functexcept.h>
36 #include <bits/move.h>
37 #if __cplusplus >= 201103L
38 #include <type_traits>
39 #endif
40 
41 namespace std _GLIBCXX_VISIBILITY(default)
42 {
43 _GLIBCXX_BEGIN_NAMESPACE_VERSION
44 
45  /**
46  * @brief An allocator that uses global `new`, as per C++03 [20.4.1].
47  * @ingroup allocators
48  *
49  * This is precisely the allocator defined in the C++ Standard.
50  * - all allocation calls `operator new`
51  * - all deallocation calls `operator delete`
52  *
53  * This is the default base-class implementation of `std::allocator`,
54  * and is also the base-class of the `__gnu_cxx::new_allocator` extension.
55  * You should use either `std::allocator` or `__gnu_cxx::new_allocator`
56  * instead of using this directly.
57  *
58  * @tparam _Tp Type of allocated object.
59  *
60  * @headerfile memory
61  */
62  template<typename _Tp>
64  {
65  public:
66  typedef _Tp value_type;
67  typedef std::size_t size_type;
68  typedef std::ptrdiff_t difference_type;
69 #if __cplusplus <= 201703L
70  typedef _Tp* pointer;
71  typedef const _Tp* const_pointer;
72  typedef _Tp& reference;
73  typedef const _Tp& const_reference;
74 
75  template<typename _Tp1>
76  struct rebind
77  { typedef __new_allocator<_Tp1> other; };
78 #endif
79 
80 #if __cplusplus >= 201103L
81  // _GLIBCXX_RESOLVE_LIB_DEFECTS
82  // 2103. propagate_on_container_move_assignment
84 #endif
85 
86  __attribute__((__always_inline__))
87  _GLIBCXX20_CONSTEXPR
88  __new_allocator() _GLIBCXX_USE_NOEXCEPT { }
89 
90  __attribute__((__always_inline__))
91  _GLIBCXX20_CONSTEXPR
92  __new_allocator(const __new_allocator&) _GLIBCXX_USE_NOEXCEPT { }
93 
94  template<typename _Tp1>
95  __attribute__((__always_inline__))
96  _GLIBCXX20_CONSTEXPR
97  __new_allocator(const __new_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
98 
99 #if __cplusplus <= 201703L
100  ~__new_allocator() _GLIBCXX_USE_NOEXCEPT { }
101 
102  pointer
103  address(reference __x) const _GLIBCXX_NOEXCEPT
104  { return std::__addressof(__x); }
105 
106  const_pointer
107  address(const_reference __x) const _GLIBCXX_NOEXCEPT
108  { return std::__addressof(__x); }
109 #endif
110 
111 #if __has_builtin(__builtin_operator_new) >= 201802L
112 # define _GLIBCXX_OPERATOR_NEW __builtin_operator_new
113 # define _GLIBCXX_OPERATOR_DELETE __builtin_operator_delete
114 #else
115 # define _GLIBCXX_OPERATOR_NEW ::operator new
116 # define _GLIBCXX_OPERATOR_DELETE ::operator delete
117 #endif
118 
119  // NB: __n is permitted to be 0. The C++ standard says nothing
120  // about what the return value is when __n == 0.
121  _GLIBCXX_NODISCARD _Tp*
122  allocate(size_type __n, const void* = static_cast<const void*>(0))
123  {
124 #if __cplusplus >= 201103L
125  // _GLIBCXX_RESOLVE_LIB_DEFECTS
126  // 3308. std::allocator<void>().allocate(n)
127  static_assert(sizeof(_Tp) != 0, "cannot allocate incomplete types");
128 #endif
129 
130  if (__builtin_expect(__n > this->_M_max_size(), false))
131  {
132  // _GLIBCXX_RESOLVE_LIB_DEFECTS
133  // 3190. allocator::allocate sometimes returns too little storage
134  if (__n > (std::size_t(-1) / sizeof(_Tp)))
135  std::__throw_bad_array_new_length();
136  std::__throw_bad_alloc();
137  }
138 
139 #if __cpp_aligned_new
140  if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
141  {
142  std::align_val_t __al = std::align_val_t(alignof(_Tp));
143  return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp),
144  __al));
145  }
146 #endif
147  return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp)));
148  }
149 
150  // __p is not permitted to be a null pointer.
151  void
152  deallocate(_Tp* __p, size_type __n __attribute__ ((__unused__)))
153  {
154 #if __cpp_sized_deallocation
155 # define _GLIBCXX_SIZED_DEALLOC(p, n) (p), (n) * sizeof(_Tp)
156 #else
157 # define _GLIBCXX_SIZED_DEALLOC(p, n) (p)
158 #endif
159 
160 #if __cpp_aligned_new
161  if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
162  {
163  _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n),
164  std::align_val_t(alignof(_Tp)));
165  return;
166  }
167 #endif
168  _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n));
169  }
170 
171 #undef _GLIBCXX_SIZED_DEALLOC
172 #undef _GLIBCXX_OPERATOR_DELETE
173 #undef _GLIBCXX_OPERATOR_NEW
174 
175 #if __cplusplus <= 201703L
176  __attribute__((__always_inline__))
177  size_type
178  max_size() const _GLIBCXX_USE_NOEXCEPT
179  { return _M_max_size(); }
180 
181 #if __cplusplus >= 201103L
182  template<typename _Up, typename... _Args>
183  __attribute__((__always_inline__))
184  void
185  construct(_Up* __p, _Args&&... __args)
187  { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
188 
189  template<typename _Up>
190  __attribute__((__always_inline__))
191  void
192  destroy(_Up* __p)
194  { __p->~_Up(); }
195 #else
196  // _GLIBCXX_RESOLVE_LIB_DEFECTS
197  // 402. wrong new expression in [some_] allocator::construct
198  __attribute__((__always_inline__))
199  void
200  construct(pointer __p, const _Tp& __val)
201  { ::new((void *)__p) _Tp(__val); }
202 
203  __attribute__((__always_inline__))
204  void
205  destroy(pointer __p) { __p->~_Tp(); }
206 #endif
207 #endif // ! C++20
208 
209  template<typename _Up>
210  friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR bool
211  operator==(const __new_allocator&, const __new_allocator<_Up>&)
212  _GLIBCXX_NOTHROW
213  { return true; }
214 
215 #if __cpp_impl_three_way_comparison < 201907L
216  template<typename _Up>
217  friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR bool
218  operator!=(const __new_allocator&, const __new_allocator<_Up>&)
219  _GLIBCXX_NOTHROW
220  { return false; }
221 #endif
222 
223  private:
224  __attribute__((__always_inline__))
225  _GLIBCXX_CONSTEXPR size_type
226  _M_max_size() const _GLIBCXX_USE_NOEXCEPT
227  {
228 #if __PTRDIFF_MAX__ < __SIZE_MAX__
229  return std::size_t(__PTRDIFF_MAX__) / sizeof(_Tp);
230 #else
231  return std::size_t(-1) / sizeof(_Tp);
232 #endif
233  }
234  };
235 
236 _GLIBCXX_END_NAMESPACE_VERSION
237 } // namespace
238 
239 #endif
integral_constant
Definition: type_traits:62
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:51
An allocator that uses global new, as per C++03 [20.4.1].This is precisely the allocator defined in t...
is_nothrow_constructible
Definition: type_traits:1113
ISO C++ entities toplevel namespace is std.
is_nothrow_destructible
Definition: type_traits:1030