libstdc++
pool_allocator.h
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1 // Allocators -*- C++ -*-
2 
3 // Copyright (C) 2001-2019 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
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10 
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15 
16 // Under Section 7 of GPL version 3, you are granted additional
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18 // 3.1, as published by the Free Software Foundation.
19 
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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
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/c++config.h>
46 #include <cstdlib>
47 #include <new>
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>
54 #endif
55 
56 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
57 {
58 _GLIBCXX_BEGIN_NAMESPACE_VERSION
59 
60  using std::size_t;
61  using std::ptrdiff_t;
62 
63  /**
64  * @brief Base class for __pool_alloc.
65  *
66  * Uses various allocators to fulfill underlying requests (and makes as
67  * few requests as possible when in default high-speed pool mode).
68  *
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.
77  */
79  {
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 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;
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
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 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  template<typename _Tp>
204  inline bool
205  operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
206  { return false; }
207 
208  template<typename _Tp>
209  _Atomic_word
210  __pool_alloc<_Tp>::_S_force_new;
211 
212  template<typename _Tp>
213  _GLIBCXX_NODISCARD _Tp*
214  __pool_alloc<_Tp>::allocate(size_type __n, const void*)
215  {
216  pointer __ret = 0;
217  if (__builtin_expect(__n != 0, true))
218  {
219  if (__n > this->max_size())
220  std::__throw_bad_alloc();
221 
222  const size_t __bytes = __n * sizeof(_Tp);
223 
224 #if __cpp_aligned_new
225  if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
226  {
227  std::align_val_t __al = std::align_val_t(alignof(_Tp));
228  return static_cast<_Tp*>(::operator new(__bytes, __al));
229  }
230 #endif
231 
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)
236  {
237  if (std::getenv("GLIBCXX_FORCE_NEW"))
238  __atomic_add_dispatch(&_S_force_new, 1);
239  else
240  __atomic_add_dispatch(&_S_force_new, -1);
241  }
242 
243  if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
244  __ret = static_cast<_Tp*>(::operator new(__bytes));
245  else
246  {
247  _Obj* volatile* __free_list = _M_get_free_list(__bytes);
248 
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)));
253  else
254  {
255  *__free_list = __result->_M_free_list_link;
256  __ret = reinterpret_cast<_Tp*>(__result);
257  }
258  if (__ret == 0)
259  std::__throw_bad_alloc();
260  }
261  }
262  return __ret;
263  }
264 
265  template<typename _Tp>
266  void
267  __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
268  {
269  if (__builtin_expect(__n != 0 && __p != 0, true))
270  {
271 #if __cpp_aligned_new
272  if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
273  {
274  ::operator delete(__p, std::align_val_t(alignof(_Tp)));
275  return;
276  }
277 #endif
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);
281  else
282  {
283  _Obj* volatile* __free_list = _M_get_free_list(__bytes);
284  _Obj* __q = reinterpret_cast<_Obj*>(__p);
285 
286  __scoped_lock sentry(_M_get_mutex());
287  __q ->_M_free_list_link = *__free_list;
288  *__free_list = __q;
289  }
290  }
291  }
292 
293 _GLIBCXX_END_NAMESPACE_VERSION
294 } // namespace
295 
296 #endif
integral_constant
Definition: type_traits:57
Base class for __pool_alloc.
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:47
GNU extensions for public use.
Allocator using a memory pool with a single lock.