libstdc++: pool_allocator.h Source File

libstdc++

pool_allocator.h
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1// Allocators -*- C++ -*-
2
3// Copyright (C) 2001-2026 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 ext/pool_allocator.h
39 * This file is a GNU extension to the Standard C++ Library.
40 */
41
42#ifndef _POOL_ALLOCATOR_H
43#define _POOL_ALLOCATOR_H 1
44
45#include <bits/requires_hosted.h> // GNU extensions are currently omitted
46
47#include <bits/c++config.h>
48#include <cstdlib>
49#include <new>
50#include <bits/new_throw.h>
51#include <ext/atomicity.h>
52#include <ext/concurrence.h>
53#include <bits/move.h>
54#if __cplusplus >= 201103L
55#include <type_traits>
56#endif
57
58namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
59{
60_GLIBCXX_BEGIN_NAMESPACE_VERSION
61
62 /**
63 * @brief Base class for __pool_alloc.
64 *
65 * Uses various allocators to fulfill underlying requests (and makes as
66 * few requests as possible when in default high-speed pool mode).
67 *
68 * Important implementation properties:
69 * 0. If globally mandated, then allocate objects from new
70 * 1. If the clients request an object of size > _S_max_bytes, the resulting
71 * object will be obtained directly from new
72 * 2. In all other cases, we allocate an object of size exactly
73 * _S_round_up(requested_size). Thus the client has enough size
74 * information that we can return the object to the proper free list
75 * without permanently losing part of the object.
76 */
77 class __pool_alloc_base
78 {
79 typedef std::size_t size_t;
80 protected:
81
82 enum { _S_align = 8 };
83 enum { _S_max_bytes = 128 };
84 enum { _S_free_list_size = (size_t)_S_max_bytes / (size_t)_S_align };
85
86 union _Obj
87 {
88 union _Obj* _M_free_list_link;
89 char _M_client_data[1]; // The client sees this.
90 };
91
92 static _Obj* volatile _S_free_list[_S_free_list_size];
93
94 // Chunk allocation state.
95 static char* _S_start_free;
96 static char* _S_end_free;
97 static size_t _S_heap_size;
98
99 size_t
100 _M_round_up(size_t __bytes)
101 { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
102
103 _GLIBCXX_CONST _Obj* volatile*
104 _M_get_free_list(size_t __bytes) throw ();
105
106 __mutex&
107 _M_get_mutex() throw ();
108
109 // Returns an object of size __n, and optionally adds to size __n
110 // free list.
111 void*
112 _M_refill(size_t __n);
113
114 // Allocates a chunk for nobjs of size size. nobjs may be reduced
115 // if it is inconvenient to allocate the requested number.
116 char*
117 _M_allocate_chunk(size_t __n, int& __nobjs);
118 };
119
120
121 /**
122 * @brief Allocator using a memory pool with a single lock.
123 * @ingroup allocators
124 */
125 template<typename _Tp>
126 class __pool_alloc : private __pool_alloc_base
127 {
128 private:
129 static _Atomic_word _S_force_new;
130
131 public:
132 typedef std::size_t size_type;
133 typedef std::ptrdiff_t difference_type;
134 typedef _Tp* pointer;
135 typedef const _Tp* const_pointer;
136 typedef _Tp& reference;
137 typedef const _Tp& const_reference;
138 typedef _Tp value_type;
139
140 template<typename _Tp1>
141 struct rebind
142 { typedef __pool_alloc<_Tp1> other; };
143
144#if __cplusplus >= 201103L
145 // _GLIBCXX_RESOLVE_LIB_DEFECTS
146 // 2103. propagate_on_container_move_assignment
147 typedef std::true_type propagate_on_container_move_assignment;
148#endif
149
150 __pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
151
152 __pool_alloc(const __pool_alloc&) _GLIBCXX_USE_NOEXCEPT { }
153
154 template<typename _Tp1>
155 __pool_alloc(const __pool_alloc<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
156
157 ~__pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
158
159 pointer
160 address(reference __x) const _GLIBCXX_NOEXCEPT
161 { return std::__addressof(__x); }
162
163 const_pointer
164 address(const_reference __x) const _GLIBCXX_NOEXCEPT
165 { return std::__addressof(__x); }
166
167 size_type
168 max_size() const _GLIBCXX_USE_NOEXCEPT
169 { return std::size_t(-1) / sizeof(_Tp); }
170
171#if __cplusplus >= 201103L
172 template<typename _Up, typename... _Args>
173 void
174 construct(_Up* __p, _Args&&... __args)
175 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
176
177 template<typename _Up>
178 void
179 destroy(_Up* __p) { __p->~_Up(); }
180#else
181 // _GLIBCXX_RESOLVE_LIB_DEFECTS
182 // 402. wrong new expression in [some_] allocator::construct
183 void
184 construct(pointer __p, const _Tp& __val)
185 { ::new((void *)__p) _Tp(__val); }
186
187 void
188 destroy(pointer __p) { __p->~_Tp(); }
189#endif
190
191 _GLIBCXX_NODISCARD pointer
192 allocate(size_type __n, const void* = 0);
193
194 void
195 deallocate(pointer __p, size_type __n);
196 };
197
198 template<typename _Tp>
199 inline bool
200 operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
201 { return true; }
202
203#if __cpp_impl_three_way_comparison < 201907L
204 template<typename _Tp>
205 inline bool
206 operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
207 { return false; }
208#endif
209
210 template<typename _Tp>
211 _Atomic_word
212 __pool_alloc<_Tp>::_S_force_new;
213
214 template<typename _Tp>
215 _GLIBCXX_NODISCARD _Tp*
216 __pool_alloc<_Tp>::allocate(size_type __n, const void*)
217 {
218 using std::size_t;
219 pointer __ret = 0;
220 if (__builtin_expect(__n != 0, true))
221 {
222 if (__n > this->max_size())
223 std::__throw_bad_alloc();
224
225 const size_t __bytes = __n * sizeof(_Tp);
226
227#if __cpp_aligned_new && __cplusplus >= 201103L
228 if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
229 {
230 std::align_val_t __al = std::align_val_t(alignof(_Tp));
231 return static_cast<_Tp*>(::operator new(__bytes, __al));
232 }
233#endif
234
235 // If there is a race through here, assume answer from getenv
236 // will resolve in same direction. Inspired by techniques
237 // to efficiently support threading found in basic_string.h.
238 if (_S_force_new == 0)
239 {
240 if (std::getenv("GLIBCXX_FORCE_NEW"))
241 __atomic_add_dispatch(&_S_force_new, 1);
242 else
243 __atomic_add_dispatch(&_S_force_new, -1);
244 }
245
246 if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
247 __ret = static_cast<_Tp*>(::operator new(__bytes));
248 else
249 {
250 _Obj* volatile* __free_list = _M_get_free_list(__bytes);
251
252 __scoped_lock sentry(_M_get_mutex());
253 _Obj* __restrict__ __result = *__free_list;
254 if (__builtin_expect(__result == 0, 0))
255 __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
256 else
257 {
258 *__free_list = __result->_M_free_list_link;
259 __ret = reinterpret_cast<_Tp*>(__result);
260 }
261 if (__ret == 0)
262 std::__throw_bad_alloc();
263 }
264 }
265 return __ret;
266 }
267
268 template<typename _Tp>
269 void
270 __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
271 {
272 using std::size_t;
273 if (__builtin_expect(__n != 0 && __p != 0, true))
274 {
275#if __cpp_aligned_new && __cplusplus >= 201103L
276 if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
277 {
278 ::operator delete(__p, std::align_val_t(alignof(_Tp)));
279 return;
280 }
281#endif
282 const size_t __bytes = __n * sizeof(_Tp);
283 if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
284 ::operator delete(__p);
285 else
286 {
287 _Obj* volatile* __free_list = _M_get_free_list(__bytes);
288 _Obj* __q = reinterpret_cast<_Obj*>(__p);
289
290 __scoped_lock sentry(_M_get_mutex());
291 __q ->_M_free_list_link = *__free_list;
292 *__free_list = __q;
293 }
294 }
295 }
296
297_GLIBCXX_END_NAMESPACE_VERSION
298} // namespace
299
300#endif
new
type_traits
cstdlib
new_throw.h
move.h
requires_hosted.h
c++config.h
atomicity.h
concurrence.h
std::true_type
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition type_traits:119
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition move.h:52
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:72
__gnu_cxx
GNU extensions for public use.
__gnu_cxx::other
__gnu_cxx::__scoped_lock
Scoped lock idiom.
Definition concurrence.h:234
__gnu_cxx::__pool_alloc_base
Base class for __pool_alloc.
Definition pool_allocator.h:78
__gnu_cxx::__pool_alloc
Allocator using a memory pool with a single lock.
Definition pool_allocator.h:127