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

   1 // Allocators -*- C++ -*-
   2
   3 // Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
   4 // Free Software Foundation, Inc.
   5 //
   6 // This file is part of the GNU ISO C++ Library.  This library is free
   7 // software; you can redistribute it and/or modify it under the
   8 // terms of the GNU General Public License as published by the
   9 // Free Software Foundation; either version 2, or (at your option)
  10 // any later version.
  11
  12 // This library is distributed in the hope that it will be useful,
  13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 // GNU General Public License for more details.
  16
  17 // You should have received a copy of the GNU General Public License along
  18 // with this library; see the file COPYING.  If not, write to the Free
  19 // Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
  20 // USA.
  21
  22 // As a special exception, you may use this file as part of a free software
  23 // library without restriction.  Specifically, if other files instantiate
  24 // templates or use macros or inline functions from this file, or you compile
  25 // this file and link it with other files to produce an executable, this
  26 // file does not by itself cause the resulting executable to be covered by
  27 // the GNU General Public License.  This exception does not however
  28 // invalidate any other reasons why the executable file might be covered by
  29 // the GNU General Public License.
  30
  31 /*
  32  * Copyright (c) 1996-1997
  33  * Silicon Graphics Computer Systems, Inc.
  34  *
  35  * Permission to use, copy, modify, distribute and sell this software
  36  * and its documentation for any purpose is hereby granted without fee,
  37  * provided that the above copyright notice appear in all copies and
  38  * that both that copyright notice and this permission notice appear
  39  * in supporting documentation.  Silicon Graphics makes no
  40  * representations about the suitability of this software for any
  41  * purpose.  It is provided "as is" without express or implied warranty.
  42  */
  43
  44 /** @file ext/pool_allocator.h
  45  *  This file is a GNU extension to the Standard C++ Library.
  46  */
  47
  48 #ifndef _POOL_ALLOCATOR_H
  49 #define _POOL_ALLOCATOR_H 1
  50
  51 #include <bits/c++config.h>
  52 #include <cstdlib>
  53 #include <new>
  54 #include <bits/functexcept.h>
  55 #include <ext/atomicity.h>
  56 #include <ext/concurrence.h>
  57 #include <bits/move.h>
  58
  59 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
  60
  61   using std::size_t;
  62   using std::ptrdiff_t;
  63
  64   /**
  65    *  @brief  Base class for __pool_alloc.
  66    *
  67    *  Uses various allocators to fulfill underlying requests (and makes as
  68    *  few requests as possible when in default high-speed pool mode).
  69    *
  70    *  Important implementation properties:
  71    *  0. If globally mandated, then allocate objects from new
  72    *  1. If the clients request an object of size > _S_max_bytes, the resulting
  73    *     object will be obtained directly from new
  74    *  2. In all other cases, we allocate an object of size exactly
  75    *     _S_round_up(requested_size).  Thus the client has enough size
  76    *     information that we can return the object to the proper free list
  77    *     without permanently losing part of the object.
  78    */
  79     class __pool_alloc_base
  80     {
  81     protected:
  82
  83       enum { _S_align = 8 };
  84       enum { _S_max_bytes = 128 };
  85       enum { _S_free_list_size = (size_t)_S_max_bytes / (size_t)_S_align };
  86
  87       union _Obj
  88       {
  89         union _Obj* _M_free_list_link;
  90         char        _M_client_data[1];    // The client sees this.
  91       };
  92
  93       static _Obj* volatile         _S_free_list[_S_free_list_size];
  94
  95       // Chunk allocation state.
  96       static char*                  _S_start_free;
  97       static char*                  _S_end_free;
  98       static size_t                 _S_heap_size;
  99
 100       size_t
 101       _M_round_up(size_t __bytes)
 102       { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
 103
 104       _Obj* volatile*
 105       _M_get_free_list(size_t __bytes);
 106
 107       __mutex&
 108       _M_get_mutex();
 109
 110       // Returns an object of size __n, and optionally adds to size __n
 111       // free list.
 112       void*
 113       _M_refill(size_t __n);
 114
 115       // Allocates a chunk for nobjs of size size.  nobjs may be reduced
 116       // if it is inconvenient to allocate the requested number.
 117       char*
 118       _M_allocate_chunk(size_t __n, int& __nobjs);
 119     };
 120
 121
 122   /**
 123    * @brief  Allocator using a memory pool with a single lock.
 124    * @ingroup allocators
 125    */
 126   template<typename _Tp>
 127     class __pool_alloc : private __pool_alloc_base
 128     {
 129     private:
 130       static _Atomic_word           _S_force_new;
 131
 132     public:
 133       typedef size_t     size_type;
 134       typedef ptrdiff_t  difference_type;
 135       typedef _Tp*       pointer;
 136       typedef const _Tp* const_pointer;
 137       typedef _Tp&       reference;
 138       typedef const _Tp& const_reference;
 139       typedef _Tp        value_type;
 140
 141       template<typename _Tp1>
 142         struct rebind
 143         { typedef __pool_alloc<_Tp1> other; };
 144
 145       __pool_alloc() throw() { }
 146
 147       __pool_alloc(const __pool_alloc&) throw() { }
 148
 149       template<typename _Tp1>
 150         __pool_alloc(const __pool_alloc<_Tp1>&) throw() { }
 151
 152       ~__pool_alloc() throw() { }
 153
 154       pointer
 155       address(reference __x) const { return &__x; }
 156
 157       const_pointer
 158       address(const_reference __x) const { return &__x; }
 159
 160       size_type
 161       max_size() const throw()
 162       { return size_t(-1) / sizeof(_Tp); }
 163
 164       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 165       // 402. wrong new expression in [some_] allocator::construct
 166       void
 167       construct(pointer __p, const _Tp& __val)
 168       { ::new((void *)__p) _Tp(__val); }
 169
 170 #ifdef __GXX_EXPERIMENTAL_CXX0X__
 171       template<typename... _Args>
 172         void
 173         construct(pointer __p, _Args&&... __args)
 174         { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
 175 #endif
 176
 177       void
 178       destroy(pointer __p) { __p->~_Tp(); }
 179
 180       pointer
 181       allocate(size_type __n, const void* = 0);
 182
 183       void
 184       deallocate(pointer __p, size_type __n);
 185     };
 186
 187   template<typename _Tp>
 188     inline bool
 189     operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 190     { return true; }
 191
 192   template<typename _Tp>
 193     inline bool
 194     operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 195     { return false; }
 196
 197   template<typename _Tp>
 198     _Atomic_word
 199     __pool_alloc<_Tp>::_S_force_new;
 200
 201   template<typename _Tp>
 202     _Tp*
 203     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
 204     {
 205       pointer __ret = 0;
 206       if (__builtin_expect(__n != 0, true))
 207         {
 208           if (__builtin_expect(__n > this->max_size(), false))
 209             std::__throw_bad_alloc();
 210
 211           // If there is a race through here, assume answer from getenv
 212           // will resolve in same direction.  Inspired by techniques
 213           // to efficiently support threading found in basic_string.h.
 214           if (_S_force_new == 0)
 215             {
 216               if (std::getenv("GLIBCXX_FORCE_NEW"))
 217                 __atomic_add_dispatch(&_S_force_new, 1);
 218               else
 219                 __atomic_add_dispatch(&_S_force_new, -1);
 220             }
 221
 222           const size_t __bytes = __n * sizeof(_Tp);
 223           if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
 224             __ret = static_cast<_Tp*>(::operator new(__bytes));
 225           else
 226             {
 227               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 228
 229               __scoped_lock sentry(_M_get_mutex());
 230               _Obj* __restrict__ __result = *__free_list;
 231               if (__builtin_expect(__result == 0, 0))
 232                 __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
 233               else
 234                 {
 235                   *__free_list = __result->_M_free_list_link;
 236                   __ret = reinterpret_cast<_Tp*>(__result);
 237                 }
 238               if (__builtin_expect(__ret == 0, 0))
 239                 std::__throw_bad_alloc();
 240             }
 241         }
 242       return __ret;
 243     }
 244
 245   template<typename _Tp>
 246     void
 247     __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
 248     {
 249       if (__builtin_expect(__n != 0 && __p != 0, true))
 250         {
 251           const size_t __bytes = __n * sizeof(_Tp);
 252           if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
 253             ::operator delete(__p);
 254           else
 255             {
 256               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 257               _Obj* __q = reinterpret_cast<_Obj*>(__p);
 258
 259               __scoped_lock sentry(_M_get_mutex());
 260               __q ->_M_free_list_link = *__free_list;
 261               *__free_list = __q;
 262             }
 263         }
 264     }
 265
 266 _GLIBCXX_END_NAMESPACE
 267
 268 #endif