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

   1 // Allocators -*- C++ -*-
   2
   3 // Copyright (C) 2001-2020 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/c++config.h>
  46 #include <cstdlib>
  47 #include <new>
  48 #include <bits/functexcept.h>
  49 #include <ext/atomicity.h>
  50 #include <ext/concurrence.h>
  51 #include <bits/move.h>
  52 #if __cplusplus >= 201103L
  53 #include <type_traits>
  54 #endif
  55
  56 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
  57 {
  58 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  59
  60   /**
  61    *  @brief  Base class for __pool_alloc.
  62    *
  63    *  Uses various allocators to fulfill underlying requests (and makes as
  64    *  few requests as possible when in default high-speed pool mode).
  65    *
  66    *  Important implementation properties:
  67    *  0. If globally mandated, then allocate objects from new
  68    *  1. If the clients request an object of size > _S_max_bytes, the resulting
  69    *     object will be obtained directly from new
  70    *  2. In all other cases, we allocate an object of size exactly
  71    *     _S_round_up(requested_size).  Thus the client has enough size
  72    *     information that we can return the object to the proper free list
  73    *     without permanently losing part of the object.
  74    */
  75     class __pool_alloc_base
  76     {
  77       typedef std::size_t size_t;
  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 std::size_t     size_type;
 131       typedef std::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 #if __cplusplus >= 201103L
 143       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 144       // 2103. propagate_on_container_move_assignment
 145       typedef std::true_type propagate_on_container_move_assignment;
 146 #endif
 147
 148       __pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
 149
 150       __pool_alloc(const __pool_alloc&) _GLIBCXX_USE_NOEXCEPT { }
 151
 152       template<typename _Tp1>
 153         __pool_alloc(const __pool_alloc<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
 154
 155       ~__pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
 156
 157       pointer
 158       address(reference __x) const _GLIBCXX_NOEXCEPT
 159       { return std::__addressof(__x); }
 160
 161       const_pointer
 162       address(const_reference __x) const _GLIBCXX_NOEXCEPT
 163       { return std::__addressof(__x); }
 164
 165       size_type
 166       max_size() const _GLIBCXX_USE_NOEXCEPT
 167       { return std::size_t(-1) / sizeof(_Tp); }
 168
 169 #if __cplusplus >= 201103L
 170       template<typename _Up, typename... _Args>
 171         void
 172         construct(_Up* __p, _Args&&... __args)
 173         { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
 174
 175       template<typename _Up>
 176         void
 177         destroy(_Up* __p) { __p->~_Up(); }
 178 #else
 179       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 180       // 402. wrong new expression in [some_] allocator::construct
 181       void
 182       construct(pointer __p, const _Tp& __val)
 183       { ::new((void *)__p) _Tp(__val); }
 184
 185       void
 186       destroy(pointer __p) { __p->~_Tp(); }
 187 #endif
 188
 189       _GLIBCXX_NODISCARD pointer
 190       allocate(size_type __n, const void* = 0);
 191
 192       void
 193       deallocate(pointer __p, size_type __n);
 194     };
 195
 196   template<typename _Tp>
 197     inline bool
 198     operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 199     { return true; }
 200
 201   template<typename _Tp>
 202     inline bool
 203     operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
 204     { return false; }
 205
 206   template<typename _Tp>
 207     _Atomic_word
 208     __pool_alloc<_Tp>::_S_force_new;
 209
 210   template<typename _Tp>
 211     _GLIBCXX_NODISCARD _Tp*
 212     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
 213     {
 214       using std::size_t;
 215       pointer __ret = 0;
 216       if (__builtin_expect(__n != 0, true))
 217         {
 218           if (__n > this->max_size())
 219             std::__throw_bad_alloc();
 220
 221           const size_t __bytes = __n * sizeof(_Tp);
 222
 223 #if __cpp_aligned_new
 224           if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
 225             {
 226               std::align_val_t __al = std::align_val_t(alignof(_Tp));
 227               return static_cast<_Tp*>(::operator new(__bytes, __al));
 228             }
 229 #endif
 230
 231           // If there is a race through here, assume answer from getenv
 232           // will resolve in same direction.  Inspired by techniques
 233           // to efficiently support threading found in basic_string.h.
 234           if (_S_force_new == 0)
 235             {
 236               if (std::getenv("GLIBCXX_FORCE_NEW"))
 237                 __atomic_add_dispatch(&_S_force_new, 1);
 238               else
 239                 __atomic_add_dispatch(&_S_force_new, -1);
 240             }
 241
 242           if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
 243             __ret = static_cast<_Tp*>(::operator new(__bytes));
 244           else
 245             {
 246               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 247
 248               __scoped_lock sentry(_M_get_mutex());
 249               _Obj* __restrict__ __result = *__free_list;
 250               if (__builtin_expect(__result == 0, 0))
 251                 __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
 252               else
 253                 {
 254                   *__free_list = __result->_M_free_list_link;
 255                   __ret = reinterpret_cast<_Tp*>(__result);
 256                 }
 257               if (__ret == 0)
 258                 std::__throw_bad_alloc();
 259             }
 260         }
 261       return __ret;
 262     }
 263
 264   template<typename _Tp>
 265     void
 266     __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
 267     {
 268       using std::size_t;
 269       if (__builtin_expect(__n != 0 && __p != 0, true))
 270         {
 271 #if __cpp_aligned_new
 272           if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
 273             {
 274               ::operator delete(__p, std::align_val_t(alignof(_Tp)));
 275               return;
 276             }
 277 #endif
 278           const size_t __bytes = __n * sizeof(_Tp);
 279           if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
 280             ::operator delete(__p);
 281           else
 282             {
 283               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
 284               _Obj* __q = reinterpret_cast<_Obj*>(__p);
 285
 286               __scoped_lock sentry(_M_get_mutex());
 287               __q ->_M_free_list_link = *__free_list;
 288               *__free_list = __q;
 289             }
 290         }
 291     }
 292
 293 _GLIBCXX_END_NAMESPACE_VERSION
 294 } // namespace
 295
 296 #endif