libstdc++-v3/include/ext/pool_allocator.h

   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 <cstdlib>
  52 #include <new>
  53 #include <bits/functexcept.h>
  54 #include <bits/atomicity.h>
  55 #include <bits/concurrence.h>
  56
  57 namespace __gnu_cxx
  58 {
  59   /**
  60    *  @if maint
  61    *  Uses various allocators to fulfill underlying requests (and makes as
  62    *  few requests as possible when in default high-speed pool mode).
  63    *
  64    *  Important implementation properties:
  65    *  0. If globally mandated, then allocate objects from new
  66    *  1. If the clients request an object of size > _S_max_bytes, the resulting
  67    *     object will be obtained directly from new
  68    *  2. In all other cases, we allocate an object of size exactly
  69    *     _S_round_up(requested_size).  Thus the client has enough size
  70    *     information that we can return the object to the proper free list
  71    *     without permanently losing part of the object.
  72    *
  73    *  @endif
  74    *  (See @link Allocators allocators info @endlink for more.)
  75    */
  76     class __pool_alloc_base
  77     {
  78     protected:
  79
  80       enum { _S_align = 8 };
  81       enum { _S_max_bytes = 128 };
  82       enum { _S_free_list_size = _S_max_bytes / _S_align };
  83
  84       union _Obj
  85       {
  86         union _Obj* _M_free_list_link;
  87         char        _M_client_data[1];    // The client sees this.
  88       };
  89
  90       static _Obj* volatile         _S_free_list[_S_free_list_size];
  91
  92       // Chunk allocation state.
  93       static char*                  _S_start_free;
  94       static char*                  _S_end_free;
  95       static size_t                 _S_heap_size;
  96
  97       size_t
  98       _M_round_up(size_t __bytes)
  99       { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
 100
 101       _Obj* volatile*
 102       _M_get_free_list(size_t __bytes);
 103
 104       mutex_type&
 105       _M_get_mutex();
 106
 107       // Returns an object of size __n, and optionally adds to size __n
 108       // free list.
 109       void*
 110       _M_refill(size_t __n);
 111
 112       // Allocates a chunk for nobjs of size size.  nobjs may be reduced
 113       // if it is inconvenient to allocate the requested number.
 114       char*
 115       _M_allocate_chunk(size_t __n, int& __nobjs);
 116     };
 117
 118
 119   template<typename _Tp>
 120     class __pool_alloc : private __pool_alloc_base
 121     {
 122     private:
 123       static _Atomic_word           _S_force_new;
 124
 125     public:
 126       typedef size_t     size_type;
 127       typedef ptrdiff_t  difference_type;
 128       typedef _Tp*       pointer;
 129       typedef const _Tp* const_pointer;
 130       typedef _Tp&       reference;
 131       typedef const _Tp& const_reference;
 132       typedef _Tp        value_type;
 133
 134       template<typename _Tp1>
 135         struct rebind
 136         { typedef __pool_alloc<_Tp1> other; };
 137
 138       __pool_alloc() throw() { }
 139
 140       __pool_alloc(const __pool_alloc&) throw() { }
 141
 142       template<typename _Tp1>
 143         __pool_alloc(const __pool_alloc<_Tp1>&) throw() { }
 144
 145       ~__pool_alloc() throw() { }
 146
 147       pointer
 148       address(reference __x) const { return &__x; }
 149
 150       const_pointer
 151       address(const_reference __x) const { return &__x; }
 152
 153       size_type
 154       max_size() const throw()
 155       { return size_t(-1) / sizeof(_Tp); }
 156
 157       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 158       // 402. wrong new expression in [some_] allocator::construct
 159       void
 160       construct(pointer __p, const _Tp& __val)
 161       { ::new(__p) _Tp(__val); }
 162
 163       void
 164       destroy(pointer __p) { __p->~_Tp(); }
 165
 166       pointer
 167       allocate(size_type __n, const void* = 0);
 168
 169       void
 170       deallocate(pointer __p, size_type __n);
 171     };
 172
 173   template<typename _Tp>
 174     inline bool
 175     operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 176     { return true; }
 177
 178   template<typename _Tp>
 179     inline bool
 180     operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 181     { return false; }
 182
 183   template<typename _Tp>
 184     _Atomic_word
 185     __pool_alloc<_Tp>::_S_force_new;
 186
 187   template<typename _Tp>
 188     _Tp*
 189     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
 190     {
 191       pointer __ret = 0;
 192       if (__builtin_expect(__n != 0, true))
 193         {
 194           if (__builtin_expect(__n > this->max_size(), false))
 195             std::__throw_bad_alloc();
 196
 197           // If there is a race through here, assume answer from getenv
 198           // will resolve in same direction.  Inspired by techniques
 199           // to efficiently support threading found in basic_string.h.
 200           if (_S_force_new == 0)
 201             {
 202               if (getenv("GLIBCXX_FORCE_NEW"))
 203                 __atomic_add(&_S_force_new, 1);
 204               else
 205                 __atomic_add(&_S_force_new, -1);
 206             }
 207
 208           const size_t __bytes = __n * sizeof(_Tp);
 209           if (__bytes > size_t(_S_max_bytes) || _S_force_new == 1)
 210             __ret = static_cast<_Tp*>(::operator new(__bytes));
 211           else
 212             {
 213               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 214
 215               lock sentry(_M_get_mutex());
 216               _Obj* __restrict__ __result = *__free_list;
 217               if (__builtin_expect(__result == 0, 0))
 218                 __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
 219               else
 220                 {
 221                   *__free_list = __result->_M_free_list_link;
 222                   __ret = reinterpret_cast<_Tp*>(__result);
 223                 }
 224               if (__builtin_expect(__ret == 0, 0))
 225                 std::__throw_bad_alloc();
 226             }
 227         }
 228       return __ret;
 229     }
 230
 231   template<typename _Tp>
 232     void
 233     __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
 234     {
 235       if (__builtin_expect(__n != 0 && __p != 0, true))
 236         {
 237           const size_t __bytes = __n * sizeof(_Tp);
 238           if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new == 1)
 239             ::operator delete(__p);
 240           else
 241             {
 242               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 243               _Obj* __q = reinterpret_cast<_Obj*>(__p);
 244
 245               lock sentry(_M_get_mutex());
 246               __q ->_M_free_list_link = *__free_list;
 247               *__free_list = __q;
 248             }
 249         }
 250     }
 251 } // namespace __gnu_cxx
 252
 253 #endif