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

   1 // Allocators -*- C++ -*-
   2
   3 // Copyright (C) 2001-2024 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 3, 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 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 /*
  26  * Copyright (c) 1996-1997
  27  * Silicon Graphics Computer Systems, Inc.
  28  *
  29  * Permission to use, copy, modify, distribute and sell this software
  30  * and its documentation for any purpose is hereby granted without fee,
  31  * provided that the above copyright notice appear in all copies and
  32  * that both that copyright notice and this permission notice appear
  33  * in supporting documentation.  Silicon Graphics makes no
  34  * representations about the suitability of this software for any
  35  * purpose.  It is provided "as is" without express or implied warranty.
  36  */
  37
  38 /** @file ext/pool_allocator.h
  39  *  This file is a GNU extension to the Standard C++ Library.
  40  */
  41
  42 #ifndef _POOL_ALLOCATOR_H
  43 #define _POOL_ALLOCATOR_H 1
  44
  45 #include <bits/requires_hosted.h> // GNU extensions are currently omitted
  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 #if __cplusplus >= 201103L
  55 #include <type_traits>
  56 #endif
  57
  58 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
  59 {
  60 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  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       typedef std::size_t size_t;
  80     protected:
  81
  82       enum { _S_align = 8 };
  83       enum { _S_max_bytes = 128 };
  84       enum { _S_free_list_size = (size_t)_S_max_bytes / (size_t)_S_align };
  85
  86       union _Obj
  87       {
  88         union _Obj* _M_free_list_link;
  89         char        _M_client_data[1];    // The client sees this.
  90       };
  91
  92       static _Obj* volatile         _S_free_list[_S_free_list_size];
  93
  94       // Chunk allocation state.
  95       static char*                  _S_start_free;
  96       static char*                  _S_end_free;
  97       static size_t                 _S_heap_size;
  98
  99       size_t
 100       _M_round_up(size_t __bytes)
 101       { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
 102
 103       _GLIBCXX_CONST _Obj* volatile*
 104       _M_get_free_list(size_t __bytes) throw ();
 105
 106       __mutex&
 107       _M_get_mutex() throw ();
 108
 109       // Returns an object of size __n, and optionally adds to size __n
 110       // free list.
 111       void*
 112       _M_refill(size_t __n);
 113
 114       // Allocates a chunk for nobjs of size size.  nobjs may be reduced
 115       // if it is inconvenient to allocate the requested number.
 116       char*
 117       _M_allocate_chunk(size_t __n, int& __nobjs);
 118     };
 119
 120
 121   /**
 122    * @brief  Allocator using a memory pool with a single lock.
 123    * @ingroup allocators
 124    */
 125   template<typename _Tp>
 126     class __pool_alloc : private __pool_alloc_base
 127     {
 128     private:
 129       static _Atomic_word           _S_force_new;
 130
 131     public:
 132       typedef std::size_t     size_type;
 133       typedef std::ptrdiff_t  difference_type;
 134       typedef _Tp*       pointer;
 135       typedef const _Tp* const_pointer;
 136       typedef _Tp&       reference;
 137       typedef const _Tp& const_reference;
 138       typedef _Tp        value_type;
 139
 140       template<typename _Tp1>
 141         struct rebind
 142         { typedef __pool_alloc<_Tp1> other; };
 143
 144 #if __cplusplus >= 201103L
 145       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 146       // 2103. propagate_on_container_move_assignment
 147       typedef std::true_type propagate_on_container_move_assignment;
 148 #endif
 149
 150       __pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
 151
 152       __pool_alloc(const __pool_alloc&) _GLIBCXX_USE_NOEXCEPT { }
 153
 154       template<typename _Tp1>
 155         __pool_alloc(const __pool_alloc<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
 156
 157       ~__pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
 158
 159       pointer
 160       address(reference __x) const _GLIBCXX_NOEXCEPT
 161       { return std::__addressof(__x); }
 162
 163       const_pointer
 164       address(const_reference __x) const _GLIBCXX_NOEXCEPT
 165       { return std::__addressof(__x); }
 166
 167       size_type
 168       max_size() const _GLIBCXX_USE_NOEXCEPT
 169       { return std::size_t(-1) / sizeof(_Tp); }
 170
 171 #if __cplusplus >= 201103L
 172       template<typename _Up, typename... _Args>
 173         void
 174         construct(_Up* __p, _Args&&... __args)
 175         { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
 176
 177       template<typename _Up>
 178         void
 179         destroy(_Up* __p) { __p->~_Up(); }
 180 #else
 181       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 182       // 402. wrong new expression in [some_] allocator::construct
 183       void
 184       construct(pointer __p, const _Tp& __val)
 185       { ::new((void *)__p) _Tp(__val); }
 186
 187       void
 188       destroy(pointer __p) { __p->~_Tp(); }
 189 #endif
 190
 191       _GLIBCXX_NODISCARD pointer
 192       allocate(size_type __n, const void* = 0);
 193
 194       void
 195       deallocate(pointer __p, size_type __n);
 196     };
 197
 198   template<typename _Tp>
 199     inline bool
 200     operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 201     { return true; }
 202
 203 #if __cpp_impl_three_way_comparison < 201907L
 204   template<typename _Tp>
 205     inline bool
 206     operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 207     { return false; }
 208 #endif
 209
 210   template<typename _Tp>
 211     _Atomic_word
 212     __pool_alloc<_Tp>::_S_force_new;
 213
 214   template<typename _Tp>
 215     _GLIBCXX_NODISCARD _Tp*
 216     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
 217     {
 218       using std::size_t;
 219       pointer __ret = 0;
 220       if (__builtin_expect(__n != 0, true))
 221         {
 222           if (__n > this->max_size())
 223             std::__throw_bad_alloc();
 224
 225           const size_t __bytes = __n * sizeof(_Tp);
 226
 227 #if __cpp_aligned_new && __cplusplus >= 201103L
 228           if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
 229             {
 230               std::align_val_t __al = std::align_val_t(alignof(_Tp));
 231               return static_cast<_Tp*>(::operator new(__bytes, __al));
 232             }
 233 #endif
 234
 235           // If there is a race through here, assume answer from getenv
 236           // will resolve in same direction.  Inspired by techniques
 237           // to efficiently support threading found in basic_string.h.
 238           if (_S_force_new == 0)
 239             {
 240               if (std::getenv("GLIBCXX_FORCE_NEW"))
 241                 __atomic_add_dispatch(&_S_force_new, 1);
 242               else
 243                 __atomic_add_dispatch(&_S_force_new, -1);
 244             }
 245
 246           if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
 247             __ret = static_cast<_Tp*>(::operator new(__bytes));
 248           else
 249             {
 250               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 251
 252               __scoped_lock sentry(_M_get_mutex());
 253               _Obj* __restrict__ __result = *__free_list;
 254               if (__builtin_expect(__result == 0, 0))
 255                 __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
 256               else
 257                 {
 258                   *__free_list = __result->_M_free_list_link;
 259                   __ret = reinterpret_cast<_Tp*>(__result);
 260                 }
 261               if (__ret == 0)
 262                 std::__throw_bad_alloc();
 263             }
 264         }
 265       return __ret;
 266     }
 267
 268   template<typename _Tp>
 269     void
 270     __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
 271     {
 272       using std::size_t;
 273       if (__builtin_expect(__n != 0 && __p != 0, true))
 274         {
 275 #if __cpp_aligned_new && __cplusplus >= 201103L
 276           if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
 277             {
 278               ::operator delete(__p, std::align_val_t(alignof(_Tp)));
 279               return;
 280             }
 281 #endif
 282           const size_t __bytes = __n * sizeof(_Tp);
 283           if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
 284             ::operator delete(__p);
 285           else
 286             {
 287               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 288               _Obj* __q = reinterpret_cast<_Obj*>(__p);
 289
 290               __scoped_lock sentry(_M_get_mutex());
 291               __q ->_M_free_list_link = *__free_list;
 292               *__free_list = __q;
 293             }
 294         }
 295     }
 296
 297 _GLIBCXX_END_NAMESPACE_VERSION
 298 } // namespace
 299
 300 #endif