1 // Allocators -*- C++ -*- 2 3 // Copyright (C) 2001-2018 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 using std::size_t; 61 using std::ptrdiff_t; 62 63 /** 64 * @brief Base class for __pool_alloc. 65 * 66 * Uses various allocators to fulfill underlying requests (and makes as 67 * few requests as possible when in default high-speed pool mode). 68 * 69 * Important implementation properties: 70 * 0. If globally mandated, then allocate objects from new 71 * 1. If the clients request an object of size > _S_max_bytes, the resulting 72 * object will be obtained directly from new 73 * 2. In all other cases, we allocate an object of size exactly 74 * _S_round_up(requested_size). Thus the client has enough size 75 * information that we can return the object to the proper free list 76 * without permanently losing part of the object. 77 */ 78 class __pool_alloc_base 79 { 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 size_t size_type; 133 typedef 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 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 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 template<typename _Tp> 204 inline bool 205 operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&) 206 { return false; } 207 208 template<typename _Tp> 209 _Atomic_word 210 __pool_alloc<_Tp>::_S_force_new; 211 212 template<typename _Tp> 213 _Tp* 214 __pool_alloc<_Tp>::allocate(size_type __n, const void*) 215 { 216 pointer __ret = 0; 217 if (__builtin_expect(__n != 0, true)) 218 { 219 if (__n > this->max_size()) 220 std::__throw_bad_alloc(); 221 222 const size_t __bytes = __n * sizeof(_Tp); 223 224 #if __cpp_aligned_new 225 if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__) 226 { 227 std::align_val_t __al = std::align_val_t(alignof(_Tp)); 228 return static_cast<_Tp*>(::operator new(__bytes, __al)); 229 } 230 #endif 231 232 // If there is a race through here, assume answer from getenv 233 // will resolve in same direction. Inspired by techniques 234 // to efficiently support threading found in basic_string.h. 235 if (_S_force_new == 0) 236 { 237 if (std::getenv("GLIBCXX_FORCE_NEW")) 238 __atomic_add_dispatch(&_S_force_new, 1); 239 else 240 __atomic_add_dispatch(&_S_force_new, -1); 241 } 242 243 if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0) 244 __ret = static_cast<_Tp*>(::operator new(__bytes)); 245 else 246 { 247 _Obj* volatile* __free_list = _M_get_free_list(__bytes); 248 249 __scoped_lock sentry(_M_get_mutex()); 250 _Obj* __restrict__ __result = *__free_list; 251 if (__builtin_expect(__result == 0, 0)) 252 __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes))); 253 else 254 { 255 *__free_list = __result->_M_free_list_link; 256 __ret = reinterpret_cast<_Tp*>(__result); 257 } 258 if (__ret == 0) 259 std::__throw_bad_alloc(); 260 } 261 } 262 return __ret; 263 } 264 265 template<typename _Tp> 266 void 267 __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n) 268 { 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 297