libstdc++
pool_allocator.h
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1 // Allocators -*- C++ -*-
2 
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16 // Under Section 7 of GPL version 3, you are granted additional
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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
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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/functexcept.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 
58 namespace __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  */
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>
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
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
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
Base class for __pool_alloc.
GNU extensions for public use.
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:111
Allocator using a memory pool with a single lock.
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:51