libstdc++
experimental/memory_resource
Go to the documentation of this file.
1 // <experimental/memory_resource> -*- C++ -*-
2 
3 // Copyright (C) 2015-2025 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 /** @file experimental/memory_resource
26  * This is a TS C++ Library header.
27  * @ingroup libfund-ts
28  */
29 
30 #ifndef _GLIBCXX_EXPERIMENTAL_MEMORY_RESOURCE
31 #define _GLIBCXX_EXPERIMENTAL_MEMORY_RESOURCE 1
32 
33 #ifdef _GLIBCXX_SYSHDR
34 #pragma GCC system_header
35 #endif
36 
37 #include <bits/requires_hosted.h> // experimental is currently omitted
38 
39 #if __cplusplus >= 201402L
40 
41 #include <memory> // align, uses_allocator, __uses_alloc
42 #include <experimental/utility> // pair, experimental::erased_type
43 #include <tuple> // tuple, forward_as_tuple
44 #include <atomic> // atomic
45 #include <new> // placement new
46 #include <cstddef> // max_align_t
47 #include <bits/new_allocator.h>
48 #include <debug/assertions.h>
49 
50 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
51 {
52 _GLIBCXX_BEGIN_NAMESPACE_VERSION
53  template<typename _Tp> class malloc_allocator;
54 _GLIBCXX_END_NAMESPACE_VERSION
55 } // namespace __gnu_cxx
56 
57 namespace std {
58 _GLIBCXX_BEGIN_NAMESPACE_VERSION
59 
60 namespace experimental {
61 inline namespace fundamentals_v2 {
62 namespace pmr {
63 #define __cpp_lib_experimental_memory_resources 201402L
64 
65  // Standard memory resources
66 
67  // 8.5 Class memory_resource
68  class memory_resource;
69 
70  // 8.6 Class template polymorphic_allocator
71  template<typename _Tp>
72  class polymorphic_allocator;
73 
74  template<typename _Alloc, typename _Resource = memory_resource>
75  class __resource_adaptor_imp;
76 
77  // 8.7 Alias template resource_adaptor
78  template<typename _Alloc>
79  using resource_adaptor = __resource_adaptor_imp<
80  typename allocator_traits<_Alloc>::template rebind_alloc<char>>;
81 
82  // 8.8 Global memory resources
83  memory_resource* new_delete_resource() noexcept;
84  memory_resource* null_memory_resource() noexcept;
85  memory_resource* get_default_resource() noexcept;
86  memory_resource* set_default_resource(memory_resource* __r) noexcept;
87 
88  // TODO 8.9 Pool resource classes
89 
90  class memory_resource
91  {
92  static constexpr size_t _S_max_align = alignof(max_align_t);
93 
94  public:
95  memory_resource() = default;
96  memory_resource(const memory_resource&) = default;
97  virtual ~memory_resource() = default;
98 
99  memory_resource& operator=(const memory_resource&) = default;
100 
101  _GLIBCXX_NODISCARD void*
102  allocate(size_t __bytes, size_t __alignment = _S_max_align)
103  { return do_allocate(__bytes, __alignment); }
104 
105  void
106  deallocate(void* __p, size_t __bytes, size_t __alignment = _S_max_align)
107  { return do_deallocate(__p, __bytes, __alignment); }
108 
109  bool
110  is_equal(const memory_resource& __other) const noexcept
111  { return do_is_equal(__other); }
112 
113  protected:
114  virtual void*
115  do_allocate(size_t __bytes, size_t __alignment) = 0;
116 
117  virtual void
118  do_deallocate(void* __p, size_t __bytes, size_t __alignment) = 0;
119 
120  virtual bool
121  do_is_equal(const memory_resource& __other) const noexcept = 0;
122  };
123 
124  inline bool
125  operator==(const memory_resource& __a, const memory_resource& __b) noexcept
126  { return &__a == &__b || __a.is_equal(__b); }
127 
128  inline bool
129  operator!=(const memory_resource& __a, const memory_resource& __b) noexcept
130  { return !(__a == __b); }
131 
132 
133  template<typename _Tp>
134  class polymorphic_allocator
135  {
136  public:
137  using value_type = _Tp;
138 
139  polymorphic_allocator() noexcept
140  : _M_resource(get_default_resource())
141  { }
142 
143  polymorphic_allocator(memory_resource* __r)
144  : _M_resource(__r)
145  { _GLIBCXX_DEBUG_ASSERT(__r); }
146 
147  polymorphic_allocator(const polymorphic_allocator& __other) = default;
148 
149  template <typename _Up>
150  polymorphic_allocator(const polymorphic_allocator<_Up>&
151  __other) noexcept
152  : _M_resource(__other.resource())
153  { }
154 
155  polymorphic_allocator&
156  operator=(const polymorphic_allocator& __rhs) = default;
157 
158  _GLIBCXX_NODISCARD _Tp* allocate(size_t __n)
159  { return static_cast<_Tp*>(_M_resource->allocate(__n * sizeof(_Tp),
160  alignof(_Tp))); }
161 
162  void
163  deallocate(_Tp* __p, size_t __n)
164  { _M_resource->deallocate(__p, __n * sizeof(_Tp), alignof(_Tp)); }
165 
166  template <typename _Tp1, typename... _Args> //used here
167  void
168  construct(_Tp1* __p, _Args&&... __args)
169  {
170  std::__uses_allocator_construct(this->resource(), __p,
171  std::forward<_Args>(__args)...);
172  }
173 
174  // Specializations for pair using piecewise construction
175  template <typename _Tp1, typename _Tp2,
176  typename... _Args1, typename... _Args2>
177  void
178  construct(pair<_Tp1, _Tp2>* __p, piecewise_construct_t,
179  tuple<_Args1...> __x, tuple<_Args2...> __y)
180  {
181  memory_resource* const __resource = this->resource();
182  auto __x_use_tag =
183  std::__use_alloc<_Tp1, memory_resource*, _Args1...>(__resource);
184  auto __y_use_tag =
185  std::__use_alloc<_Tp2, memory_resource*, _Args2...>(__resource);
186 
187  ::new(__p) std::pair<_Tp1, _Tp2>(piecewise_construct,
188  _M_construct_p(__x_use_tag, __x),
189  _M_construct_p(__y_use_tag, __y));
190  }
191 
192  template <typename _Tp1, typename _Tp2>
193  void
194  construct(pair<_Tp1,_Tp2>* __p)
195  { this->construct(__p, piecewise_construct, tuple<>(), tuple<>()); }
196 
197  template <typename _Tp1, typename _Tp2, typename _Up, typename _Vp>
198  void
199  construct(pair<_Tp1,_Tp2>* __p, _Up&& __x, _Vp&& __y)
200  {
201  this->construct(__p, piecewise_construct,
202  std::forward_as_tuple(std::forward<_Up>(__x)),
203  std::forward_as_tuple(std::forward<_Vp>(__y)));
204  }
205 
206  template <typename _Tp1, typename _Tp2, typename _Up, typename _Vp>
207  void
208  construct(pair<_Tp1,_Tp2>* __p, const std::pair<_Up, _Vp>& __pr)
209  {
210  this->construct(__p, piecewise_construct,
211  std::forward_as_tuple(__pr.first),
212  std::forward_as_tuple(__pr.second));
213  }
214 
215  template <typename _Tp1, typename _Tp2, typename _Up, typename _Vp>
216  void
217  construct(pair<_Tp1,_Tp2>* __p, pair<_Up, _Vp>&& __pr)
218  {
219  this->construct(__p, piecewise_construct,
220  std::forward_as_tuple(std::forward<_Up>(__pr.first)),
221  std::forward_as_tuple(std::forward<_Vp>(__pr.second)));
222  }
223 
224  template <typename _Up>
225  void
226  destroy(_Up* __p)
227  { __p->~_Up(); }
228 
229  // Return a default-constructed allocator (no allocator propagation)
230  polymorphic_allocator
231  select_on_container_copy_construction() const
232  { return polymorphic_allocator(); }
233 
234  memory_resource* resource() const { return _M_resource; }
235 
236  private:
237  using __uses_alloc1_ = __uses_alloc1<memory_resource*>;
238  using __uses_alloc2_ = __uses_alloc2<memory_resource*>;
239 
240  template<typename _Tuple>
241  _Tuple&&
242  _M_construct_p(__uses_alloc0, _Tuple& __t)
243  { return std::move(__t); }
244 
245  template<typename... _Args>
246  decltype(auto)
247  _M_construct_p(__uses_alloc1_ __ua, tuple<_Args...>& __t)
248  { return tuple_cat(make_tuple(allocator_arg, *(__ua._M_a)),
249  std::move(__t)); }
250 
251  template<typename... _Args>
252  decltype(auto)
253  _M_construct_p(__uses_alloc2_ __ua, tuple<_Args...>& __t)
254  { return tuple_cat(std::move(__t), make_tuple(*(__ua._M_a))); }
255 
256  memory_resource* _M_resource;
257  };
258 
259  template <class _Tp1, class _Tp2>
260  bool
261  operator==(const polymorphic_allocator<_Tp1>& __a,
262  const polymorphic_allocator<_Tp2>& __b) noexcept
263  { return *__a.resource() == *__b.resource(); }
264 
265  template <class _Tp1, class _Tp2>
266  bool
267  operator!=(const polymorphic_allocator<_Tp1>& __a,
268  const polymorphic_allocator<_Tp2>& __b) noexcept
269  { return !(__a == __b); }
270 
271 
272  /// @cond undocumented
273  class __resource_adaptor_common
274  {
275  template<typename, typename> friend class __resource_adaptor_imp;
276 
277  struct _AlignMgr
278  {
279  _AlignMgr(size_t __nbytes, size_t __align)
280  : _M_nbytes(__nbytes), _M_align(__align)
281  { }
282 
283  // Total size that needs to be allocated.
284  size_t
285  _M_alloc_size() const { return _M_buf_size() + _M_token_size(); }
286 
287  void*
288  _M_adjust(void* __ptr) const
289  {
290  const auto __orig_ptr = static_cast<char*>(__ptr);
291  size_t __space = _M_buf_size();
292  // Align the pointer within the buffer:
293  std::align(_M_align, _M_nbytes, __ptr, __space);
294  const auto __aligned_ptr = static_cast<char*>(__ptr);
295  const auto __token_size = _M_token_size();
296  // Store token immediately after the aligned block:
297  char* const __end = __aligned_ptr + _M_nbytes;
298  if (__token_size == 1)
299  _S_write<unsigned char>(__end, __aligned_ptr - __orig_ptr);
300  else if (__token_size == sizeof(short))
301  _S_write<unsigned short>(__end, __aligned_ptr - __orig_ptr);
302  else if (__token_size == sizeof(int) && sizeof(int) < sizeof(char*))
303  _S_write<unsigned int>(__end, __aligned_ptr - __orig_ptr);
304  else // (__token_size == sizeof(char*))
305  // Just store the original pointer:
306  _S_write<char*>(__end, __orig_ptr);
307  return __aligned_ptr;
308  }
309 
310  char*
311  _M_unadjust(char* __ptr) const
312  {
313  const char* const __end = __ptr + _M_nbytes;
314  char* __orig_ptr;
315  const auto __token_size = _M_token_size();
316  // Read the token and restore the original pointer:
317  if (__token_size == 1)
318  __orig_ptr = __ptr - _S_read<unsigned char>(__end);
319  else if (__token_size == sizeof(short))
320  __orig_ptr = __ptr - _S_read<unsigned short>(__end);
321  else if (__token_size == sizeof(int)
322  && sizeof(int) < sizeof(char*))
323  __orig_ptr = __ptr - _S_read<unsigned int>(__end);
324  else // (__token_size == sizeof(char*))
325  __orig_ptr = _S_read<char*>(__end);
326  // The adjustment is always less than the requested alignment,
327  // so if that isn't true now then either the wrong size was passed
328  // to deallocate or the token was overwritten by a buffer overflow:
329  __glibcxx_assert(static_cast<size_t>(__ptr - __orig_ptr) < _M_align);
330  return __orig_ptr;
331  }
332 
333  private:
334  size_t _M_nbytes;
335  size_t _M_align;
336 
337  // Number of bytes needed to fit block of given size and alignment.
338  size_t
339  _M_buf_size() const { return _M_nbytes + _M_align - 1; }
340 
341  // Number of additional bytes needed to write the token.
342  int
343  _M_token_size() const
344  {
345  if (_M_align <= (1ul << __CHAR_BIT__))
346  return 1;
347  if (_M_align <= (1ul << (sizeof(short) * __CHAR_BIT__)))
348  return sizeof(short);
349  if (_M_align <= (1ull << (sizeof(int) * __CHAR_BIT__)))
350  return sizeof(int);
351  return sizeof(char*);
352  }
353 
354  template<typename _Tp>
355  static void
356  _S_write(void* __to, _Tp __val)
357  { __builtin_memcpy(__to, &__val, sizeof(_Tp)); }
358 
359  template<typename _Tp>
360  static _Tp
361  _S_read(const void* __from)
362  {
363  _Tp __val;
364  __builtin_memcpy(&__val, __from, sizeof(_Tp));
365  return __val;
366  }
367  };
368  };
369  /// @endcond
370 
371  // 8.7.1 __resource_adaptor_imp
372  template<typename _Alloc, typename _Resource>
373  class __resource_adaptor_imp
374  : public _Resource, private __resource_adaptor_common
375  {
376  using memory_resource = _Resource;
377 
378  static_assert(is_same<char,
379  typename allocator_traits<_Alloc>::value_type>::value,
380  "Allocator's value_type is char");
381  static_assert(is_same<char*,
382  typename allocator_traits<_Alloc>::pointer>::value,
383  "Allocator's pointer type is value_type*");
384  static_assert(is_same<const char*,
385  typename allocator_traits<_Alloc>::const_pointer>::value,
386  "Allocator's const_pointer type is value_type const*");
387  static_assert(is_same<void*,
388  typename allocator_traits<_Alloc>::void_pointer>::value,
389  "Allocator's void_pointer type is void*");
390  static_assert(is_same<const void*,
391  typename allocator_traits<_Alloc>::const_void_pointer>::value,
392  "Allocator's const_void_pointer type is void const*");
393 
394  public:
395  using allocator_type = _Alloc;
396 
397  __resource_adaptor_imp() = default;
398  __resource_adaptor_imp(const __resource_adaptor_imp&) = default;
399  __resource_adaptor_imp(__resource_adaptor_imp&&) = default;
400 
401  explicit __resource_adaptor_imp(const _Alloc& __a2)
402  : _M_alloc(__a2)
403  { }
404 
405  explicit __resource_adaptor_imp(_Alloc&& __a2)
406  : _M_alloc(std::move(__a2))
407  { }
408 
409  __resource_adaptor_imp&
410  operator=(const __resource_adaptor_imp&) = default;
411 
412  allocator_type get_allocator() const noexcept { return _M_alloc; }
413 
414  protected:
415 #if (defined __sun__ || defined __VXWORKS__) && defined __i386__
416 // Cannot use max_align_t on 32-bit Solaris x86, see PR libstdc++/77691
417 # define _GLIBCXX_MAX_ALIGN_MATCHES_MALLOC 0
418 #elif defined __hpux__ && defined __hppa__ && defined __LP64__
419 // Ignore inconsistent long double and malloc alignment (libstdc++/77691)
420 # define _GLIBCXX_MAX_ALIGN_MATCHES_MALLOC 0
421 #else
422 # define _GLIBCXX_MAX_ALIGN_MATCHES_MALLOC 1
423 #endif
424 
425  virtual void*
426  do_allocate(size_t __bytes, size_t __alignment) override
427  {
428 #if _GLIBCXX_MAX_ALIGN_MATCHES_MALLOC
429  if (__alignment == alignof(max_align_t))
430  return _M_allocate<alignof(max_align_t)>(__bytes);
431 #endif
432  switch (__alignment)
433  {
434  case 1:
435  return _M_alloc.allocate(__bytes);
436  case 2:
437  return _M_allocate<2>(__bytes);
438  case 4:
439  return _M_allocate<4>(__bytes);
440  case 8:
441  return _M_allocate<8>(__bytes);
442  }
443  const _AlignMgr __mgr(__bytes, __alignment);
444  // Assume _M_alloc returns 1-byte aligned memory, so allocate enough
445  // space to fit a block of the right size and alignment, plus some
446  // extra bytes to store a token for retrieving the original pointer.
447  return __mgr._M_adjust(_M_alloc.allocate(__mgr._M_alloc_size()));
448  }
449 
450  virtual void
451  do_deallocate(void* __ptr, size_t __bytes, size_t __alignment) noexcept
452  override
453  {
454 #if _GLIBCXX_MAX_ALIGN_MATCHES_MALLOC
455  if (__alignment == alignof(max_align_t))
456  return (void) _M_deallocate<alignof(max_align_t)>(__ptr, __bytes);
457 #endif
458  switch (__alignment)
459  {
460  case 1:
461  return (void) _M_alloc.deallocate((char*)__ptr, __bytes);
462  case 2:
463  return (void) _M_deallocate<2>(__ptr, __bytes);
464  case 4:
465  return (void) _M_deallocate<4>(__ptr, __bytes);
466  case 8:
467  return (void) _M_deallocate<8>(__ptr, __bytes);
468  }
469  const _AlignMgr __mgr(__bytes, __alignment);
470  // Use the stored token to retrieve the original pointer.
471  _M_alloc.deallocate(__mgr._M_unadjust((char*)__ptr),
472  __mgr._M_alloc_size());
473  }
474 
475  virtual bool
476  do_is_equal(const memory_resource& __other) const noexcept override
477  {
478 #if __cpp_rtti
479  if (auto __p = dynamic_cast<const __resource_adaptor_imp*>(&__other))
480  return _M_alloc == __p->_M_alloc;
481 #else
482  if (this == &__other) // Need RTTI to do better than this.
483  return true;
484 #endif
485  return false;
486  }
487 
488  private:
489  template<size_t _Num>
490  struct _Aligned_type { alignas(_Num) char __c[_Num]; };
491 
492  // Rebind the allocator to the specified type and use it to allocate.
493  template<size_t _Num, typename _Tp = _Aligned_type<_Num>>
494  void*
495  _M_allocate(size_t __bytes)
496  {
497  typename allocator_traits<_Alloc>::template
498  rebind_alloc<_Tp> __a2(_M_alloc);
499  const size_t __n = (__bytes + _Num - 1) / _Num;
500  return __a2.allocate(__n);
501  }
502 
503  // Rebind the allocator to the specified type and use it to deallocate.
504  template<size_t _Num, typename _Tp = _Aligned_type<_Num>>
505  void
506  _M_deallocate(void* __ptr, size_t __bytes) noexcept
507  {
508  typename allocator_traits<_Alloc>::template
509  rebind_alloc<_Tp> __a2(_M_alloc);
510  const size_t __n = (__bytes + _Num - 1) / _Num;
511  __a2.deallocate((_Tp*)__ptr, __n);
512  }
513 
514  _Alloc _M_alloc{};
515  };
516 
517  // Global memory resources
518 
519  inline memory_resource*
520  new_delete_resource() noexcept
521  {
522  using type = resource_adaptor<std::__new_allocator<char>>;
523  alignas(type) static unsigned char __buf[sizeof(type)];
524  static type* __r = new(__buf) type;
525  return __r;
526  }
527 
528  inline memory_resource*
529  null_memory_resource() noexcept
530  {
531  class type final : public memory_resource
532  {
533  void*
534  do_allocate(size_t, size_t) override
535  { std::__throw_bad_alloc(); }
536 
537  void
538  do_deallocate(void*, size_t, size_t) noexcept override
539  { }
540 
541  bool
542  do_is_equal(const memory_resource& __other) const noexcept override
543  { return this == &__other; }
544  };
545 
546  alignas(type) static unsigned char __buf[sizeof(type)];
547  static type* __r = new(__buf) type;
548  return __r;
549  }
550 
551  // The default memory resource
552 
553  /// @cond undocumented
554  inline auto&
555  __get_default_resource()
556  {
557 #ifndef _GLIBCXX_HAS_GTHREADS
558  struct type {
559  using value_type = memory_resource*;
560  explicit type(value_type __r) : _M_r(__r) { }
561  value_type _M_r;
562  value_type load() const { return _M_r; }
563  value_type exchange(value_type __r) { return std::__exchange(_M_r, __r); }
564  };
565 #else
566  using type = atomic<memory_resource*>;
567 #endif
568  alignas(type) static unsigned char __buf[sizeof(type)];
569  static type* __r = new(__buf) type(new_delete_resource());
570  return *__r;
571  }
572  /// @endcond
573 
574  /// Get the current default resource.
575  inline memory_resource*
576  get_default_resource() noexcept
577  { return __get_default_resource().load(); }
578 
579  /// Change the default resource and return the previous one.
580  inline memory_resource*
581  set_default_resource(memory_resource* __r) noexcept
582  {
583  if (__r == nullptr)
584  __r = new_delete_resource();
585  return __get_default_resource().exchange(__r);
586  }
587 
588 } // namespace pmr
589 } // namespace fundamentals_v2
590 } // namespace experimental
591 
592 _GLIBCXX_END_NAMESPACE_VERSION
593 } // namespace std
594 #endif // C++14
595 #endif // _GLIBCXX_EXPERIMENTAL_MEMORY_RESOURCE