1 // Allocators -*- C++ -*-
3 // Copyright (C) 2001-2018 Free Software Foundation, Inc.
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)
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.
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.
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/>.
26 * Copyright (c) 1996-1997
27 * Silicon Graphics Computer Systems, Inc.
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.
38 /** @file ext/pool_allocator.h
39 * This file is a GNU extension to the Standard C++ Library.
42 #ifndef _POOL_ALLOCATOR_H
43 #define _POOL_ALLOCATOR_H 1
45 #include <bits/c++config.h>
48 #include <bits/functexcept.h>
49 #include <ext/atomicity.h>
50 #include <ext/concurrence.h>
51 #include <bits/move.h>
52 #if __cplusplus >= 201103L
53 #include <type_traits>
56 namespace __gnu_cxx
_GLIBCXX_VISIBILITY(default)
58 _GLIBCXX_BEGIN_NAMESPACE_VERSION
64 * @brief Base class for __pool_alloc.
66 * Uses various allocators to fulfill underlying requests (and makes as
67 * few requests as possible when in default high-speed pool mode).
69 * Important implementation properties:
70 * 0. If globally mandated, then allocate objects from new
71 * 1. If the clients request an object of size > _S_max_bytes, the resulting
72 * object will be obtained directly from new
73 * 2. In all other cases, we allocate an object of size exactly
74 * _S_round_up(requested_size). Thus the client has enough size
75 * information that we can return the object to the proper free list
76 * without permanently losing part of the object.
78 class __pool_alloc_base
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
};
88 union _Obj
* _M_free_list_link
;
89 char _M_client_data
[1]; // The client sees this.
92 static _Obj
* volatile _S_free_list
[_S_free_list_size
];
94 // Chunk allocation state.
95 static char* _S_start_free
;
96 static char* _S_end_free
;
97 static size_t _S_heap_size
;
100 _M_round_up(size_t __bytes
)
101 { return ((__bytes
+ (size_t)_S_align
- 1) & ~((size_t)_S_align
- 1)); }
103 _GLIBCXX_CONST _Obj
* volatile*
104 _M_get_free_list(size_t __bytes
) throw ();
107 _M_get_mutex() throw ();
109 // Returns an object of size __n, and optionally adds to size __n
112 _M_refill(size_t __n
);
114 // Allocates a chunk for nobjs of size size. nobjs may be reduced
115 // if it is inconvenient to allocate the requested number.
117 _M_allocate_chunk(size_t __n
, int& __nobjs
);
122 * @brief Allocator using a memory pool with a single lock.
123 * @ingroup allocators
125 template<typename _Tp
>
126 class __pool_alloc
: private __pool_alloc_base
129 static _Atomic_word _S_force_new
;
132 typedef size_t size_type
;
133 typedef 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
;
140 template<typename _Tp1
>
142 { typedef __pool_alloc
<_Tp1
> other
; };
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
;
150 __pool_alloc() _GLIBCXX_USE_NOEXCEPT
{ }
152 __pool_alloc(const __pool_alloc
&) _GLIBCXX_USE_NOEXCEPT
{ }
154 template<typename _Tp1
>
155 __pool_alloc(const __pool_alloc
<_Tp1
>&) _GLIBCXX_USE_NOEXCEPT
{ }
157 ~__pool_alloc() _GLIBCXX_USE_NOEXCEPT
{ }
160 address(reference __x
) const _GLIBCXX_NOEXCEPT
161 { return std::__addressof(__x
); }
164 address(const_reference __x
) const _GLIBCXX_NOEXCEPT
165 { return std::__addressof(__x
); }
168 max_size() const _GLIBCXX_USE_NOEXCEPT
169 { return size_t(-1) / sizeof(_Tp
); }
171 #if __cplusplus >= 201103L
172 template<typename _Up
, typename
... _Args
>
174 construct(_Up
* __p
, _Args
&&... __args
)
175 { ::new((void *)__p
) _Up(std::forward
<_Args
>(__args
)...); }
177 template<typename _Up
>
179 destroy(_Up
* __p
) { __p
->~_Up(); }
181 // _GLIBCXX_RESOLVE_LIB_DEFECTS
182 // 402. wrong new expression in [some_] allocator::construct
184 construct(pointer __p
, const _Tp
& __val
)
185 { ::new((void *)__p
) _Tp(__val
); }
188 destroy(pointer __p
) { __p
->~_Tp(); }
192 allocate(size_type __n
, const void* = 0);
195 deallocate(pointer __p
, size_type __n
);
198 template<typename _Tp
>
200 operator==(const __pool_alloc
<_Tp
>&, const __pool_alloc
<_Tp
>&)
203 template<typename _Tp
>
205 operator!=(const __pool_alloc
<_Tp
>&, const __pool_alloc
<_Tp
>&)
208 template<typename _Tp
>
210 __pool_alloc
<_Tp
>::_S_force_new
;
212 template<typename _Tp
>
214 __pool_alloc
<_Tp
>::allocate(size_type __n
, const void*)
217 if (__builtin_expect(__n
!= 0, true))
219 if (__n
> this->max_size())
220 std::__throw_bad_alloc();
222 const size_t __bytes
= __n
* sizeof(_Tp
);
224 #if __cpp_aligned_new
225 if (alignof(_Tp
) > __STDCPP_DEFAULT_NEW_ALIGNMENT__
)
227 std::align_val_t __al
= std::align_val_t(alignof(_Tp
));
228 return static_cast<_Tp
*>(::operator new(__bytes
, __al
));
232 // If there is a race through here, assume answer from getenv
233 // will resolve in same direction. Inspired by techniques
234 // to efficiently support threading found in basic_string.h.
235 if (_S_force_new
== 0)
237 if (std::getenv("GLIBCXX_FORCE_NEW"))
238 __atomic_add_dispatch(&_S_force_new
, 1);
240 __atomic_add_dispatch(&_S_force_new
, -1);
243 if (__bytes
> size_t(_S_max_bytes
) || _S_force_new
> 0)
244 __ret
= static_cast<_Tp
*>(::operator new(__bytes
));
247 _Obj
* volatile* __free_list
= _M_get_free_list(__bytes
);
249 __scoped_lock
sentry(_M_get_mutex());
250 _Obj
* __restrict__ __result
= *__free_list
;
251 if (__builtin_expect(__result
== 0, 0))
252 __ret
= static_cast<_Tp
*>(_M_refill(_M_round_up(__bytes
)));
255 *__free_list
= __result
->_M_free_list_link
;
256 __ret
= reinterpret_cast<_Tp
*>(__result
);
259 std::__throw_bad_alloc();
265 template<typename _Tp
>
267 __pool_alloc
<_Tp
>::deallocate(pointer __p
, size_type __n
)
269 if (__builtin_expect(__n
!= 0 && __p
!= 0, true))
271 #if __cpp_aligned_new
272 if (alignof(_Tp
) > __STDCPP_DEFAULT_NEW_ALIGNMENT__
)
274 ::operator delete(__p
, std::align_val_t(alignof(_Tp
)));
278 const size_t __bytes
= __n
* sizeof(_Tp
);
279 if (__bytes
> static_cast<size_t>(_S_max_bytes
) || _S_force_new
> 0)
280 ::operator delete(__p
);
283 _Obj
* volatile* __free_list
= _M_get_free_list(__bytes
);
284 _Obj
* __q
= reinterpret_cast<_Obj
*>(__p
);
286 __scoped_lock
sentry(_M_get_mutex());
287 __q
->_M_free_list_link
= *__free_list
;
293 _GLIBCXX_END_NAMESPACE_VERSION