pool_allocator.h revision 132720 
1// Allocators -*- C++ -*-
2
3// Copyright (C) 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
4//
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 2, or (at your option)
9// any later version.
10
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.
15
16// You should have received a copy of the GNU General Public License along
17// with this library; see the file COPYING.  If not, write to the Free
18// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
19// USA.
20
21// As a special exception, you may use this file as part of a free software
22// library without restriction.  Specifically, if other files instantiate
23// templates or use macros or inline functions from this file, or you compile
24// this file and link it with other files to produce an executable, this
25// file does not by itself cause the resulting executable to be covered by
26// the GNU General Public License.  This exception does not however
27// invalidate any other reasons why the executable file might be covered by
28// the GNU General Public License.
29
30/*
31 * Copyright (c) 1996-1997
32 * Silicon Graphics Computer Systems, Inc.
33 *
34 * Permission to use, copy, modify, distribute and sell this software
35 * and its documentation for any purpose is hereby granted without fee,
36 * provided that the above copyright notice appear in all copies and
37 * that both that copyright notice and this permission notice appear
38 * in supporting documentation.  Silicon Graphics makes no
39 * representations about the suitability of this software for any
40 * purpose.  It is provided "as is" without express or implied warranty.
41 */
42
43/** @file ext/pool_allocator.h
44 *  This file is a GNU extension to the Standard C++ Library.
45 *  You should only include this header if you are using GCC 3 or later.
46 */
47#ifndef _POOL_ALLOCATOR_H
48#define _POOL_ALLOCATOR_H 1
49
50#include <bits/c++config.h>
51#include <new>
52#include <bits/functexcept.h>
53#include <bits/atomicity.h>
54#include <bits/concurrence.h>
55
56namespace __gnu_cxx
57{
58  /**
59   *  @if maint
60   *  Uses various allocators to fulfill underlying requests (and makes as
61   *  few requests as possible when in default high-speed pool mode).
62   *
63   *  Important implementation properties:
64   *  0. If globally mandated, then allocate objects from new
65   *  1. If the clients request an object of size > _S_max_bytes, the resulting
66   *     object will be obtained directly from new
67   *  2. In all other cases, we allocate an object of size exactly
68   *     _S_round_up(requested_size).  Thus the client has enough size
69   *     information that we can return the object to the proper free list
70   *     without permanently losing part of the object.
71   *
72   *  @endif
73   *  (See @link Allocators allocators info @endlink for more.)
74   */
75    class __pool_base
76    {
77    protected:
78
79      enum { _S_align = 8 };
80      enum { _S_max_bytes = 128 };
81      enum { _S_free_list_size = _S_max_bytes / _S_align };
82
83      union _Obj
84      {
85	union _Obj* _M_free_list_link;
86	char        _M_client_data[1];    // The client sees this.
87      };
88
89      static _Obj* volatile         _S_free_list[_S_free_list_size];
90
91      // Chunk allocation state.
92      static char*                  _S_start_free;
93      static char*                  _S_end_free;
94      static size_t                 _S_heap_size;
95
96      size_t
97      _M_round_up(size_t __bytes)
98      { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
99
100      _Obj* volatile*
101      _M_get_free_list(size_t __bytes);
102
103      mutex_type&
104      _M_get_mutex();
105
106      // Returns an object of size __n, and optionally adds to size __n
107      // free list.
108      void*
109      _M_refill(size_t __n);
110
111      // Allocates a chunk for nobjs of size size.  nobjs may be reduced
112      // if it is inconvenient to allocate the requested number.
113      char*
114      _M_allocate_chunk(size_t __n, int& __nobjs);
115    };
116
117
118  template<typename _Tp>
119    class __pool_alloc : private __pool_base
120    {
121    private:
122      static _Atomic_word	    _S_force_new;
123
124    public:
125      typedef size_t     size_type;
126      typedef ptrdiff_t  difference_type;
127      typedef _Tp*       pointer;
128      typedef const _Tp* const_pointer;
129      typedef _Tp&       reference;
130      typedef const _Tp& const_reference;
131      typedef _Tp        value_type;
132
133      template<typename _Tp1>
134        struct rebind
135        { typedef __pool_alloc<_Tp1> other; };
136
137      __pool_alloc() throw() { }
138
139      __pool_alloc(const __pool_alloc&) throw() { }
140
141      template<typename _Tp1>
142        __pool_alloc(const __pool_alloc<_Tp1>&) throw() { }
143
144      ~__pool_alloc() throw() { }
145
146      pointer
147      address(reference __x) const { return &__x; }
148
149      const_pointer
150      address(const_reference __x) const { return &__x; }
151
152      size_type
153      max_size() const throw()
154      { return size_t(-1) / sizeof(_Tp); }
155
156      // _GLIBCXX_RESOLVE_LIB_DEFECTS
157      // 402. wrong new expression in [some_] allocator::construct
158      void
159      construct(pointer __p, const _Tp& __val)
160      { ::new(__p) _Tp(__val); }
161
162      void
163      destroy(pointer __p) { __p->~_Tp(); }
164
165      pointer
166      allocate(size_type __n, const void* = 0);
167
168      void
169      deallocate(pointer __p, size_type __n);
170    };
171
172  template<typename _Tp>
173    inline bool
174    operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
175    { return true; }
176
177  template<typename _Tp>
178    inline bool
179    operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
180    { return false; }
181
182  template<typename _Tp>
183    _Atomic_word
184    __pool_alloc<_Tp>::_S_force_new;
185
186  template<typename _Tp>
187    _Tp*
188    __pool_alloc<_Tp>::allocate(size_type __n, const void*)
189    {
190      pointer __ret = 0;
191      if (__n)
192	{
193	  if (__n <= max_size())
194	    {
195	      // If there is a race through here, assume answer from getenv
196	      // will resolve in same direction.  Inspired by techniques
197	      // to efficiently support threading found in basic_string.h.
198	      if (_S_force_new == 0)
199		{
200		  if (getenv("GLIBCXX_FORCE_NEW"))
201		    __atomic_add(&_S_force_new, 1);
202		  else
203		    __atomic_add(&_S_force_new, -1);
204		}
205
206	      const size_t __bytes = __n * sizeof(_Tp);
207	      if (__bytes > size_t(_S_max_bytes) || _S_force_new == 1)
208		__ret = static_cast<_Tp*>(::operator new(__bytes));
209	      else
210		{
211		  _Obj* volatile* __free_list = _M_get_free_list(__bytes);
212
213		  lock sentry(_M_get_mutex());
214		  _Obj* __restrict__ __result = *__free_list;
215		  if (__builtin_expect(__result == 0, 0))
216		    __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
217		  else
218		    {
219		      *__free_list = __result->_M_free_list_link;
220		      __ret = reinterpret_cast<_Tp*>(__result);
221		    }
222		  if (__builtin_expect(__ret == 0, 0))
223		    std::__throw_bad_alloc();
224		}
225	    }
226	  else
227	    std::__throw_bad_alloc();
228	}
229      return __ret;
230    }
231
232  template<typename _Tp>
233    void
234    __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
235    {
236      if (__n)
237	{
238	  const size_t __bytes = __n * sizeof(_Tp);
239	  if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new == 1)
240	    ::operator delete(__p);
241	  else
242	    {
243	      _Obj* volatile* __free_list = _M_get_free_list(__bytes);
244	      _Obj* __q = reinterpret_cast<_Obj*>(__p);
245
246	      lock sentry(_M_get_mutex());
247	      __q ->_M_free_list_link = *__free_list;
248	      *__free_list = __q;
249	    }
250	}
251    }
252} // namespace __gnu_cxx
253
254#endif
255