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

   1 // Allocators -*- C++ -*-
   2
   3 // Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
   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 3, 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 // Under Section 7 of GPL version 3, you are granted additional
  18 // permissions described in the GCC Runtime Library Exception, version
  19 // 3.1, as published by the Free Software Foundation.
  20
  21 // You should have received a copy of the GNU General Public License and
  22 // a copy of the GCC Runtime Library Exception along with this program;
  23 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  24 // <http://www.gnu.org/licenses/>.
  25
  26 /*
  27  * Copyright (c) 1996-1997
  28  * Silicon Graphics Computer Systems, Inc.
  29  *
  30  * Permission to use, copy, modify, distribute and sell this software
  31  * and its documentation for any purpose is hereby granted without fee,
  32  * provided that the above copyright notice appear in all copies and
  33  * that both that copyright notice and this permission notice appear
  34  * in supporting documentation.  Silicon Graphics makes no
  35  * representations about the suitability of this software for any
  36  * purpose.  It is provided "as is" without express or implied warranty.
  37  */
  38
  39 /** @file ext/pool_allocator.h
  40  *  This file is a GNU extension to the Standard C++ Library.
  41  */
  42
  43 #ifndef _POOL_ALLOCATOR_H
  44 #define _POOL_ALLOCATOR_H 1
  45
  46 #include <bits/c++config.h>
  47 #include <cstdlib>
  48 #include <new>
  49 #include <bits/functexcept.h>
  50 #include <ext/atomicity.h>
  51 #include <ext/concurrence.h>
  52 #include <bits/move.h>
  53
  54 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
  55 {
  56 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  57
  58   using std::size_t;
  59   using std::ptrdiff_t;
  60
  61   /**
  62    *  @brief  Base class for __pool_alloc.
  63    *
  64    *  Uses various allocators to fulfill underlying requests (and makes as
  65    *  few requests as possible when in default high-speed pool mode).
  66    *
  67    *  Important implementation properties:
  68    *  0. If globally mandated, then allocate objects from new
  69    *  1. If the clients request an object of size > _S_max_bytes, the resulting
  70    *     object will be obtained directly from new
  71    *  2. In all other cases, we allocate an object of size exactly
  72    *     _S_round_up(requested_size).  Thus the client has enough size
  73    *     information that we can return the object to the proper free list
  74    *     without permanently losing part of the object.
  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 = (size_t)_S_max_bytes / (size_t)_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       _GLIBCXX_CONST _Obj* volatile*
 102       _M_get_free_list(size_t __bytes) throw ();
 103
 104       __mutex&
 105       _M_get_mutex() throw ();
 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   /**
 120    * @brief  Allocator using a memory pool with a single lock.
 121    * @ingroup allocators
 122    */
 123   template<typename _Tp>
 124     class __pool_alloc : private __pool_alloc_base
 125     {
 126     private:
 127       static _Atomic_word           _S_force_new;
 128
 129     public:
 130       typedef size_t     size_type;
 131       typedef ptrdiff_t  difference_type;
 132       typedef _Tp*       pointer;
 133       typedef const _Tp* const_pointer;
 134       typedef _Tp&       reference;
 135       typedef const _Tp& const_reference;
 136       typedef _Tp        value_type;
 137
 138       template<typename _Tp1>
 139         struct rebind
 140         { typedef __pool_alloc<_Tp1> other; };
 141
 142       __pool_alloc() throw() { }
 143
 144       __pool_alloc(const __pool_alloc&) throw() { }
 145
 146       template<typename _Tp1>
 147         __pool_alloc(const __pool_alloc<_Tp1>&) throw() { }
 148
 149       ~__pool_alloc() throw() { }
 150
 151       pointer
 152       address(reference __x) const { return std::__addressof(__x); }
 153
 154       const_pointer
 155       address(const_reference __x) const { return std::__addressof(__x); }
 156
 157       size_type
 158       max_size() const throw()
 159       { return size_t(-1) / sizeof(_Tp); }
 160
 161       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 162       // 402. wrong new expression in [some_] allocator::construct
 163       void
 164       construct(pointer __p, const _Tp& __val)
 165       { ::new((void *)__p) _Tp(__val); }
 166
 167 #ifdef __GXX_EXPERIMENTAL_CXX0X__
 168       template<typename... _Args>
 169         void
 170         construct(pointer __p, _Args&&... __args)
 171         { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
 172 #endif
 173
 174       void
 175       destroy(pointer __p) { __p->~_Tp(); }
 176
 177       pointer
 178       allocate(size_type __n, const void* = 0);
 179
 180       void
 181       deallocate(pointer __p, size_type __n);
 182     };
 183
 184   template<typename _Tp>
 185     inline bool
 186     operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 187     { return true; }
 188
 189   template<typename _Tp>
 190     inline bool
 191     operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 192     { return false; }
 193
 194   template<typename _Tp>
 195     _Atomic_word
 196     __pool_alloc<_Tp>::_S_force_new;
 197
 198   template<typename _Tp>
 199     _Tp*
 200     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
 201     {
 202       pointer __ret = 0;
 203       if (__builtin_expect(__n != 0, true))
 204         {
 205           if (__n > this->max_size())
 206             std::__throw_bad_alloc();
 207
 208           // If there is a race through here, assume answer from getenv
 209           // will resolve in same direction.  Inspired by techniques
 210           // to efficiently support threading found in basic_string.h.
 211           if (_S_force_new == 0)
 212             {
 213               if (std::getenv("GLIBCXX_FORCE_NEW"))
 214                 __atomic_add_dispatch(&_S_force_new, 1);
 215               else
 216                 __atomic_add_dispatch(&_S_force_new, -1);
 217             }
 218
 219           const size_t __bytes = __n * sizeof(_Tp);
 220           if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
 221             __ret = static_cast<_Tp*>(::operator new(__bytes));
 222           else
 223             {
 224               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 225
 226               __scoped_lock sentry(_M_get_mutex());
 227               _Obj* __restrict__ __result = *__free_list;
 228               if (__builtin_expect(__result == 0, 0))
 229                 __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
 230               else
 231                 {
 232                   *__free_list = __result->_M_free_list_link;
 233                   __ret = reinterpret_cast<_Tp*>(__result);
 234                 }
 235               if (__ret == 0)
 236                 std::__throw_bad_alloc();
 237             }
 238         }
 239       return __ret;
 240     }
 241
 242   template<typename _Tp>
 243     void
 244     __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
 245     {
 246       if (__builtin_expect(__n != 0 && __p != 0, true))
 247         {
 248           const size_t __bytes = __n * sizeof(_Tp);
 249           if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
 250             ::operator delete(__p);
 251           else
 252             {
 253               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 254               _Obj* __q = reinterpret_cast<_Obj*>(__p);
 255
 256               __scoped_lock sentry(_M_get_mutex());
 257               __q ->_M_free_list_link = *__free_list;
 258               *__free_list = __q;
 259             }
 260         }
 261     }
 262
 263 _GLIBCXX_END_NAMESPACE_VERSION
 264 } // namespace
 265
 266 #endif