libstdc++
pool_allocator.h
Go to the documentation of this file.
1 // Allocators -*- C++ -*-
2 
3 // Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
4 // 2010, 2011
5 // Free Software Foundation, Inc.
6 //
7 // This file is part of the GNU ISO C++ Library. This library is free
8 // software; you can redistribute it and/or modify it under the
9 // terms of the GNU General Public License as published by the
10 // Free Software Foundation; either version 3, or (at your option)
11 // any later version.
12 
13 // This library is distributed in the hope that it will be useful,
14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 // GNU General Public License for more details.
17 
18 // Under Section 7 of GPL version 3, you are granted additional
19 // permissions described in the GCC Runtime Library Exception, version
20 // 3.1, as published by the Free Software Foundation.
21 
22 // You should have received a copy of the GNU General Public License and
23 // a copy of the GCC Runtime Library Exception along with this program;
24 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
25 // <http://www.gnu.org/licenses/>.
26 
27 /*
28  * Copyright (c) 1996-1997
29  * Silicon Graphics Computer Systems, Inc.
30  *
31  * Permission to use, copy, modify, distribute and sell this software
32  * and its documentation for any purpose is hereby granted without fee,
33  * provided that the above copyright notice appear in all copies and
34  * that both that copyright notice and this permission notice appear
35  * in supporting documentation. Silicon Graphics makes no
36  * representations about the suitability of this software for any
37  * purpose. It is provided "as is" without express or implied warranty.
38  */
39 
40 /** @file ext/pool_allocator.h
41  * This file is a GNU extension to the Standard C++ Library.
42  */
43 
44 #ifndef _POOL_ALLOCATOR_H
45 #define _POOL_ALLOCATOR_H 1
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 
55 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
56 {
57 _GLIBCXX_BEGIN_NAMESPACE_VERSION
58 
59  using std::size_t;
60  using std::ptrdiff_t;
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  protected:
80 
81  enum { _S_align = 8 };
82  enum { _S_max_bytes = 128 };
83  enum { _S_free_list_size = (size_t)_S_max_bytes / (size_t)_S_align };
84 
85  union _Obj
86  {
87  union _Obj* _M_free_list_link;
88  char _M_client_data[1]; // The client sees this.
89  };
90 
91  static _Obj* volatile _S_free_list[_S_free_list_size];
92 
93  // Chunk allocation state.
94  static char* _S_start_free;
95  static char* _S_end_free;
96  static size_t _S_heap_size;
97 
98  size_t
99  _M_round_up(size_t __bytes)
100  { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
101 
102  _GLIBCXX_CONST _Obj* volatile*
103  _M_get_free_list(size_t __bytes) throw ();
104 
105  __mutex&
106  _M_get_mutex() throw ();
107 
108  // Returns an object of size __n, and optionally adds to size __n
109  // free list.
110  void*
111  _M_refill(size_t __n);
112 
113  // Allocates a chunk for nobjs of size size. nobjs may be reduced
114  // if it is inconvenient to allocate the requested number.
115  char*
116  _M_allocate_chunk(size_t __n, int& __nobjs);
117  };
118 
119 
120  /**
121  * @brief Allocator using a memory pool with a single lock.
122  * @ingroup allocators
123  */
124  template<typename _Tp>
126  {
127  private:
128  static _Atomic_word _S_force_new;
129 
130  public:
131  typedef size_t size_type;
132  typedef ptrdiff_t difference_type;
133  typedef _Tp* pointer;
134  typedef const _Tp* const_pointer;
135  typedef _Tp& reference;
136  typedef const _Tp& const_reference;
137  typedef _Tp value_type;
138 
139  template<typename _Tp1>
140  struct rebind
141  { typedef __pool_alloc<_Tp1> other; };
142 
143  __pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
144 
145  __pool_alloc(const __pool_alloc&) _GLIBCXX_USE_NOEXCEPT { }
146 
147  template<typename _Tp1>
148  __pool_alloc(const __pool_alloc<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
149 
150  ~__pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
151 
152  pointer
153  address(reference __x) const _GLIBCXX_NOEXCEPT
154  { return std::__addressof(__x); }
155 
156  const_pointer
157  address(const_reference __x) const _GLIBCXX_NOEXCEPT
158  { return std::__addressof(__x); }
159 
160  size_type
161  max_size() const _GLIBCXX_USE_NOEXCEPT
162  { return size_t(-1) / sizeof(_Tp); }
163 
164 #ifdef __GXX_EXPERIMENTAL_CXX0X__
165  template<typename _Up, typename... _Args>
166  void
167  construct(_Up* __p, _Args&&... __args)
168  { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
169 
170  template<typename _Up>
171  void
172  destroy(_Up* __p) { __p->~_Up(); }
173 #else
174  // _GLIBCXX_RESOLVE_LIB_DEFECTS
175  // 402. wrong new expression in [some_] allocator::construct
176  void
177  construct(pointer __p, const _Tp& __val)
178  { ::new((void *)__p) _Tp(__val); }
179 
180  void
181  destroy(pointer __p) { __p->~_Tp(); }
182 #endif
183 
184  pointer
185  allocate(size_type __n, const void* = 0);
186 
187  void
188  deallocate(pointer __p, size_type __n);
189  };
190 
191  template<typename _Tp>
192  inline bool
193  operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
194  { return true; }
195 
196  template<typename _Tp>
197  inline bool
198  operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
199  { return false; }
200 
201  template<typename _Tp>
202  _Atomic_word
203  __pool_alloc<_Tp>::_S_force_new;
204 
205  template<typename _Tp>
206  _Tp*
207  __pool_alloc<_Tp>::allocate(size_type __n, const void*)
208  {
209  pointer __ret = 0;
210  if (__builtin_expect(__n != 0, true))
211  {
212  if (__n > this->max_size())
213  std::__throw_bad_alloc();
214 
215  // If there is a race through here, assume answer from getenv
216  // will resolve in same direction. Inspired by techniques
217  // to efficiently support threading found in basic_string.h.
218  if (_S_force_new == 0)
219  {
220  if (std::getenv("GLIBCXX_FORCE_NEW"))
221  __atomic_add_dispatch(&_S_force_new, 1);
222  else
223  __atomic_add_dispatch(&_S_force_new, -1);
224  }
225 
226  const size_t __bytes = __n * sizeof(_Tp);
227  if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
228  __ret = static_cast<_Tp*>(::operator new(__bytes));
229  else
230  {
231  _Obj* volatile* __free_list = _M_get_free_list(__bytes);
232 
233  __scoped_lock sentry(_M_get_mutex());
234  _Obj* __restrict__ __result = *__free_list;
235  if (__builtin_expect(__result == 0, 0))
236  __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
237  else
238  {
239  *__free_list = __result->_M_free_list_link;
240  __ret = reinterpret_cast<_Tp*>(__result);
241  }
242  if (__ret == 0)
243  std::__throw_bad_alloc();
244  }
245  }
246  return __ret;
247  }
248 
249  template<typename _Tp>
250  void
251  __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
252  {
253  if (__builtin_expect(__n != 0 && __p != 0, true))
254  {
255  const size_t __bytes = __n * sizeof(_Tp);
256  if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
257  ::operator delete(__p);
258  else
259  {
260  _Obj* volatile* __free_list = _M_get_free_list(__bytes);
261  _Obj* __q = reinterpret_cast<_Obj*>(__p);
262 
263  __scoped_lock sentry(_M_get_mutex());
264  __q ->_M_free_list_link = *__free_list;
265  *__free_list = __q;
266  }
267  }
268  }
269 
270 _GLIBCXX_END_NAMESPACE_VERSION
271 } // namespace
272 
273 #endif