1 // Allocators -*- C++ -*-
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26 * Copyright (c) 1996-1997
27 * Silicon Graphics Computer Systems, Inc.
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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
61 * @brief Base class for __pool_alloc.
63 * Uses various allocators to fulfill underlying requests (and makes as
64 * few requests as possible when in default high-speed pool mode).
66 * Important implementation properties:
67 * 0. If globally mandated, then allocate objects from new
68 * 1. If the clients request an object of size > _S_max_bytes, the resulting
69 * object will be obtained directly from new
70 * 2. In all other cases, we allocate an object of size exactly
71 * _S_round_up(requested_size). Thus the client has enough size
72 * information that we can return the object to the proper free list
73 * without permanently losing part of the object.
75 class __pool_alloc_base
77 typedef std::size_t size_t;
80 enum { _S_align
= 8 };
81 enum { _S_max_bytes
= 128 };
82 enum { _S_free_list_size
= (size_t)_S_max_bytes
/ (size_t)_S_align
};
86 union _Obj
* _M_free_list_link
;
87 char _M_client_data
[1]; // The client sees this.
90 static _Obj
* volatile _S_free_list
[_S_free_list_size
];
92 // Chunk allocation state.
93 static char* _S_start_free
;
94 static char* _S_end_free
;
95 static size_t _S_heap_size
;
98 _M_round_up(size_t __bytes
)
99 { return ((__bytes
+ (size_t)_S_align
- 1) & ~((size_t)_S_align
- 1)); }
101 _GLIBCXX_CONST _Obj
* volatile*
102 _M_get_free_list(size_t __bytes
) throw ();
105 _M_get_mutex() throw ();
107 // Returns an object of size __n, and optionally adds to size __n
110 _M_refill(size_t __n
);
112 // Allocates a chunk for nobjs of size size. nobjs may be reduced
113 // if it is inconvenient to allocate the requested number.
115 _M_allocate_chunk(size_t __n
, int& __nobjs
);
120 * @brief Allocator using a memory pool with a single lock.
121 * @ingroup allocators
123 template<typename _Tp
>
124 class __pool_alloc
: private __pool_alloc_base
127 static _Atomic_word _S_force_new
;
130 typedef std::size_t size_type
;
131 typedef std::ptrdiff_t difference_type
;
132 typedef _Tp
* pointer
;
133 typedef const _Tp
* const_pointer
;
134 typedef _Tp
& reference
;
135 typedef const _Tp
& const_reference
;
136 typedef _Tp value_type
;
138 template<typename _Tp1
>
140 { typedef __pool_alloc
<_Tp1
> other
; };
142 #if __cplusplus >= 201103L
143 // _GLIBCXX_RESOLVE_LIB_DEFECTS
144 // 2103. propagate_on_container_move_assignment
145 typedef std::true_type propagate_on_container_move_assignment
;
148 __pool_alloc() _GLIBCXX_USE_NOEXCEPT
{ }
150 __pool_alloc(const __pool_alloc
&) _GLIBCXX_USE_NOEXCEPT
{ }
152 template<typename _Tp1
>
153 __pool_alloc(const __pool_alloc
<_Tp1
>&) _GLIBCXX_USE_NOEXCEPT
{ }
155 ~__pool_alloc() _GLIBCXX_USE_NOEXCEPT
{ }
158 address(reference __x
) const _GLIBCXX_NOEXCEPT
159 { return std::__addressof(__x
); }
162 address(const_reference __x
) const _GLIBCXX_NOEXCEPT
163 { return std::__addressof(__x
); }
166 max_size() const _GLIBCXX_USE_NOEXCEPT
167 { return std::size_t(-1) / sizeof(_Tp
); }
169 #if __cplusplus >= 201103L
170 template<typename _Up
, typename
... _Args
>
172 construct(_Up
* __p
, _Args
&&... __args
)
173 { ::new((void *)__p
) _Up(std::forward
<_Args
>(__args
)...); }
175 template<typename _Up
>
177 destroy(_Up
* __p
) { __p
->~_Up(); }
179 // _GLIBCXX_RESOLVE_LIB_DEFECTS
180 // 402. wrong new expression in [some_] allocator::construct
182 construct(pointer __p
, const _Tp
& __val
)
183 { ::new((void *)__p
) _Tp(__val
); }
186 destroy(pointer __p
) { __p
->~_Tp(); }
189 _GLIBCXX_NODISCARD pointer
190 allocate(size_type __n
, const void* = 0);
193 deallocate(pointer __p
, size_type __n
);
196 template<typename _Tp
>
198 operator==(const __pool_alloc
<_Tp
>&, const __pool_alloc
<_Tp
>&)
201 #if __cpp_impl_three_way_comparison < 201907L
202 template<typename _Tp
>
204 operator!=(const __pool_alloc
<_Tp
>&, const __pool_alloc
<_Tp
>&)
208 template<typename _Tp
>
210 __pool_alloc
<_Tp
>::_S_force_new
;
212 template<typename _Tp
>
213 _GLIBCXX_NODISCARD _Tp
*
214 __pool_alloc
<_Tp
>::allocate(size_type __n
, const void*)
218 if (__builtin_expect(__n
!= 0, true))
220 if (__n
> this->max_size())
221 std::__throw_bad_alloc();
223 const size_t __bytes
= __n
* sizeof(_Tp
);
225 #if __cpp_aligned_new
226 if (alignof(_Tp
) > __STDCPP_DEFAULT_NEW_ALIGNMENT__
)
228 std::align_val_t __al
= std::align_val_t(alignof(_Tp
));
229 return static_cast<_Tp
*>(::operator new(__bytes
, __al
));
233 // If there is a race through here, assume answer from getenv
234 // will resolve in same direction. Inspired by techniques
235 // to efficiently support threading found in basic_string.h.
236 if (_S_force_new
== 0)
238 if (std::getenv("GLIBCXX_FORCE_NEW"))
239 __atomic_add_dispatch(&_S_force_new
, 1);
241 __atomic_add_dispatch(&_S_force_new
, -1);
244 if (__bytes
> size_t(_S_max_bytes
) || _S_force_new
> 0)
245 __ret
= static_cast<_Tp
*>(::operator new(__bytes
));
248 _Obj
* volatile* __free_list
= _M_get_free_list(__bytes
);
250 __scoped_lock
sentry(_M_get_mutex());
251 _Obj
* __restrict__ __result
= *__free_list
;
252 if (__builtin_expect(__result
== 0, 0))
253 __ret
= static_cast<_Tp
*>(_M_refill(_M_round_up(__bytes
)));
256 *__free_list
= __result
->_M_free_list_link
;
257 __ret
= reinterpret_cast<_Tp
*>(__result
);
260 std::__throw_bad_alloc();
266 template<typename _Tp
>
268 __pool_alloc
<_Tp
>::deallocate(pointer __p
, size_type __n
)
271 if (__builtin_expect(__n
!= 0 && __p
!= 0, true))
273 #if __cpp_aligned_new
274 if (alignof(_Tp
) > __STDCPP_DEFAULT_NEW_ALIGNMENT__
)
276 ::operator delete(__p
, std::align_val_t(alignof(_Tp
)));
280 const size_t __bytes
= __n
* sizeof(_Tp
);
281 if (__bytes
> static_cast<size_t>(_S_max_bytes
) || _S_force_new
> 0)
282 ::operator delete(__p
);
285 _Obj
* volatile* __free_list
= _M_get_free_list(__bytes
);
286 _Obj
* __q
= reinterpret_cast<_Obj
*>(__p
);
288 __scoped_lock
sentry(_M_get_mutex());
289 __q
->_M_free_list_link
= *__free_list
;
295 _GLIBCXX_END_NAMESPACE_VERSION