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

   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    */
  77     class __pool_alloc_base
  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>
 125     class __pool_alloc : private __pool_alloc_base
 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 #if __cplusplus >= 201103L
 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