libcxx/include/__memory/shared_ptr.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___MEMORY_SHARED_PTR_H
  11 #define _LIBCPP___MEMORY_SHARED_PTR_H
  12
  13 #include <__compare/compare_three_way.h>
  14 #include <__compare/ordering.h>
  15 #include <__config>
  16 #include <__cstddef/nullptr_t.h>
  17 #include <__cstddef/ptrdiff_t.h>
  18 #include <__exception/exception.h>
  19 #include <__functional/binary_function.h>
  20 #include <__functional/operations.h>
  21 #include <__functional/reference_wrapper.h>
  22 #include <__fwd/ostream.h>
  23 #include <__iterator/access.h>
  24 #include <__memory/addressof.h>
  25 #include <__memory/allocation_guard.h>
  26 #include <__memory/allocator.h>
  27 #include <__memory/allocator_destructor.h>
  28 #include <__memory/allocator_traits.h>
  29 #include <__memory/auto_ptr.h>
  30 #include <__memory/compressed_pair.h>
  31 #include <__memory/construct_at.h>
  32 #include <__memory/pointer_traits.h>
  33 #include <__memory/shared_count.h>
  34 #include <__memory/uninitialized_algorithms.h>
  35 #include <__memory/unique_ptr.h>
  36 #include <__type_traits/add_lvalue_reference.h>
  37 #include <__type_traits/conditional.h>
  38 #include <__type_traits/conjunction.h>
  39 #include <__type_traits/disjunction.h>
  40 #include <__type_traits/enable_if.h>
  41 #include <__type_traits/integral_constant.h>
  42 #include <__type_traits/is_array.h>
  43 #include <__type_traits/is_bounded_array.h>
  44 #include <__type_traits/is_constructible.h>
  45 #include <__type_traits/is_convertible.h>
  46 #include <__type_traits/is_reference.h>
  47 #include <__type_traits/is_same.h>
  48 #include <__type_traits/is_unbounded_array.h>
  49 #include <__type_traits/nat.h>
  50 #include <__type_traits/negation.h>
  51 #include <__type_traits/remove_cv.h>
  52 #include <__type_traits/remove_extent.h>
  53 #include <__type_traits/remove_reference.h>
  54 #include <__utility/declval.h>
  55 #include <__utility/forward.h>
  56 #include <__utility/move.h>
  57 #include <__utility/swap.h>
  58 #include <__verbose_abort>
  59 #include <new>
  60 #include <typeinfo>
  61 #if _LIBCPP_HAS_ATOMIC_HEADER
  62 #  include <__atomic/memory_order.h>
  63 #endif
  64
  65 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  66 #  pragma GCC system_header
  67 #endif
  68
  69 _LIBCPP_PUSH_MACROS
  70 #include <__undef_macros>
  71
  72 _LIBCPP_BEGIN_NAMESPACE_STD
  73
  74 class _LIBCPP_EXPORTED_FROM_ABI bad_weak_ptr : public std::exception {
  75 public:
  76   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr() _NOEXCEPT                               = default;
  77   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr(const bad_weak_ptr&) _NOEXCEPT            = default;
  78   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr& operator=(const bad_weak_ptr&) _NOEXCEPT = default;
  79   ~bad_weak_ptr() _NOEXCEPT override;
  80   const char* what() const _NOEXCEPT override;
  81 };
  82
  83 [[__noreturn__]] inline _LIBCPP_HIDE_FROM_ABI void __throw_bad_weak_ptr() {
  84 #if _LIBCPP_HAS_EXCEPTIONS
  85   throw bad_weak_ptr();
  86 #else
  87   _LIBCPP_VERBOSE_ABORT("bad_weak_ptr was thrown in -fno-exceptions mode");
  88 #endif
  89 }
  90
  91 template <class _Tp>
  92 class _LIBCPP_TEMPLATE_VIS weak_ptr;
  93
  94 template <class _Tp, class _Dp, class _Alloc>
  95 class __shared_ptr_pointer : public __shared_weak_count {
  96   _LIBCPP_COMPRESSED_TRIPLE(_Tp, __ptr_, _Dp, __deleter_, _Alloc, __alloc_);
  97
  98 public:
  99   _LIBCPP_HIDE_FROM_ABI __shared_ptr_pointer(_Tp __p, _Dp __d, _Alloc __a)
 100       : __ptr_(__p), __deleter_(std::move(__d)), __alloc_(std::move(__a)) {}
 101
 102 #if _LIBCPP_HAS_RTTI
 103   _LIBCPP_HIDE_FROM_ABI_VIRTUAL const void* __get_deleter(const type_info&) const _NOEXCEPT override;
 104 #endif
 105
 106 private:
 107   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override;
 108   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override;
 109 };
 110
 111 #if _LIBCPP_HAS_RTTI
 112
 113 template <class _Tp, class _Dp, class _Alloc>
 114 const void* __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__get_deleter(const type_info& __t) const _NOEXCEPT {
 115   return __t == typeid(_Dp) ? std::addressof(__deleter_) : nullptr;
 116 }
 117
 118 #endif // _LIBCPP_HAS_RTTI
 119
 120 template <class _Tp, class _Dp, class _Alloc>
 121 void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared() _NOEXCEPT {
 122   __deleter_(__ptr_);
 123   __deleter_.~_Dp();
 124 }
 125
 126 template <class _Tp, class _Dp, class _Alloc>
 127 void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared_weak() _NOEXCEPT {
 128   typedef typename __allocator_traits_rebind<_Alloc, __shared_ptr_pointer>::type _Al;
 129   typedef allocator_traits<_Al> _ATraits;
 130   typedef pointer_traits<typename _ATraits::pointer> _PTraits;
 131
 132   _Al __a(__alloc_);
 133   __alloc_.~_Alloc();
 134   __a.deallocate(_PTraits::pointer_to(*this), 1);
 135 }
 136
 137 // This tag is used to instantiate an allocator type. The various shared_ptr control blocks
 138 // detect that the allocator has been instantiated for this type and perform alternative
 139 // initialization/destruction based on that.
 140 struct __for_overwrite_tag {};
 141
 142 template <class _Tp, class _Alloc>
 143 struct __shared_ptr_emplace : __shared_weak_count {
 144   using __value_type = __remove_cv_t<_Tp>;
 145
 146   template <class... _Args,
 147             class _Allocator                                                                         = _Alloc,
 148             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 149   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&...) : __storage_(std::move(__a)) {
 150     static_assert(
 151         sizeof...(_Args) == 0, "No argument should be provided to the control block when using _for_overwrite");
 152     ::new (static_cast<void*>(__get_elem())) __value_type;
 153   }
 154
 155   template <class... _Args,
 156             class _Allocator                                                                          = _Alloc,
 157             __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 158   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&... __args) : __storage_(std::move(__a)) {
 159     using _TpAlloc = typename __allocator_traits_rebind<_Alloc, __value_type>::type;
 160     _TpAlloc __tmp(*__get_alloc());
 161     allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), std::forward<_Args>(__args)...);
 162   }
 163
 164   _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT { return __storage_.__get_alloc(); }
 165
 166   _LIBCPP_HIDE_FROM_ABI __value_type* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }
 167
 168 private:
 169   template <class _Allocator                                                                         = _Alloc,
 170             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 171   _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
 172     __get_elem()->~__value_type();
 173   }
 174
 175   template <class _Allocator                                                                          = _Alloc,
 176             __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 177   _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
 178     using _TpAlloc = typename __allocator_traits_rebind<_Allocator, __remove_cv_t<_Tp> >::type;
 179     _TpAlloc __tmp(*__get_alloc());
 180     allocator_traits<_TpAlloc>::destroy(__tmp, __get_elem());
 181   }
 182
 183   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override { __on_zero_shared_impl(); }
 184
 185   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
 186     using _ControlBlockAlloc   = typename __allocator_traits_rebind<_Alloc, __shared_ptr_emplace>::type;
 187     using _ControlBlockPointer = typename allocator_traits<_ControlBlockAlloc>::pointer;
 188     _ControlBlockAlloc __tmp(*__get_alloc());
 189     __storage_.~_Storage();
 190     allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, pointer_traits<_ControlBlockPointer>::pointer_to(*this), 1);
 191   }
 192
 193   // TODO: It should be possible to refactor this to remove `_Storage` entirely.
 194   // This class implements the control block for non-array shared pointers created
 195   // through `std::allocate_shared` and `std::make_shared`.
 196   struct _Storage {
 197     struct _Data {
 198       _LIBCPP_COMPRESSED_PAIR(_Alloc, __alloc_, __value_type, __elem_);
 199     };
 200
 201     _ALIGNAS_TYPE(_Data) char __buffer_[sizeof(_Data)];
 202
 203     _LIBCPP_HIDE_FROM_ABI explicit _Storage(_Alloc&& __a) { ::new ((void*)__get_alloc()) _Alloc(std::move(__a)); }
 204     _LIBCPP_HIDE_FROM_ABI ~_Storage() { __get_alloc()->~_Alloc(); }
 205
 206     _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT {
 207       return std::addressof(reinterpret_cast<_Data*>(__buffer_)->__alloc_);
 208     }
 209
 210     _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI __value_type* __get_elem() _NOEXCEPT {
 211       return std::addressof(reinterpret_cast<_Data*>(__buffer_)->__elem_);
 212     }
 213   };
 214
 215   _Storage __storage_;
 216 };
 217
 218 struct __shared_ptr_dummy_rebind_allocator_type;
 219 template <>
 220 class _LIBCPP_TEMPLATE_VIS allocator<__shared_ptr_dummy_rebind_allocator_type> {
 221 public:
 222   template <class _Other>
 223   struct rebind {
 224     typedef allocator<_Other> other;
 225   };
 226 };
 227
 228 template <class _Tp>
 229 class _LIBCPP_TEMPLATE_VIS enable_shared_from_this;
 230
 231 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.general-6
 232 // A pointer type Y* is said to be compatible with a pointer type T*
 233 // when either Y* is convertible to T* or Y is U[N] and T is cv U[].
 234 #if _LIBCPP_STD_VER >= 17
 235 template <class _Yp, class _Tp>
 236 struct __bounded_convertible_to_unbounded : false_type {};
 237
 238 template <class _Up, std::size_t _Np, class _Tp>
 239 struct __bounded_convertible_to_unbounded<_Up[_Np], _Tp> : is_same<__remove_cv_t<_Tp>, _Up[]> {};
 240
 241 template <class _Yp, class _Tp>
 242 struct __compatible_with : _Or< is_convertible<_Yp*, _Tp*>, __bounded_convertible_to_unbounded<_Yp, _Tp> > {};
 243 #else
 244 template <class _Yp, class _Tp>
 245 struct __compatible_with : is_convertible<_Yp*, _Tp*> {};
 246 #endif // _LIBCPP_STD_VER >= 17
 247
 248 // Constructors that take raw pointers have a different set of "compatible" constraints
 249 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.const-9.1
 250 // - If T is an array type, then either T is U[N] and Y(*)[N] is convertible to T*,
 251 //   or T is U[] and Y(*)[] is convertible to T*.
 252 // - If T is not an array type, then Y* is convertible to T*.
 253 #if _LIBCPP_STD_VER >= 17
 254 template <class _Yp, class _Tp, class = void>
 255 struct __raw_pointer_compatible_with : _And< _Not<is_array<_Tp>>, is_convertible<_Yp*, _Tp*> > {};
 256
 257 template <class _Yp, class _Up, std::size_t _Np>
 258 struct __raw_pointer_compatible_with<_Yp, _Up[_Np], __enable_if_t< is_convertible<_Yp (*)[_Np], _Up (*)[_Np]>::value> >
 259     : true_type {};
 260
 261 template <class _Yp, class _Up>
 262 struct __raw_pointer_compatible_with<_Yp, _Up[], __enable_if_t< is_convertible<_Yp (*)[], _Up (*)[]>::value> >
 263     : true_type {};
 264
 265 #else
 266 template <class _Yp, class _Tp>
 267 struct __raw_pointer_compatible_with : is_convertible<_Yp*, _Tp*> {};
 268 #endif // _LIBCPP_STD_VER >= 17
 269
 270 template <class _Ptr, class = void>
 271 struct __is_deletable : false_type {};
 272 template <class _Ptr>
 273 struct __is_deletable<_Ptr, decltype(delete std::declval<_Ptr>())> : true_type {};
 274
 275 template <class _Ptr, class = void>
 276 struct __is_array_deletable : false_type {};
 277 template <class _Ptr>
 278 struct __is_array_deletable<_Ptr, decltype(delete[] std::declval<_Ptr>())> : true_type {};
 279
 280 template <class _Dp, class _Pt, class = decltype(std::declval<_Dp>()(std::declval<_Pt>()))>
 281 true_type __well_formed_deleter_test(int);
 282
 283 template <class, class>
 284 false_type __well_formed_deleter_test(...);
 285
 286 template <class _Dp, class _Pt>
 287 struct __well_formed_deleter : decltype(std::__well_formed_deleter_test<_Dp, _Pt>(0)) {};
 288
 289 template <class _Dp, class _Yp, class _Tp>
 290 struct __shared_ptr_deleter_ctor_reqs {
 291   static const bool value = __raw_pointer_compatible_with<_Yp, _Tp>::value && is_move_constructible<_Dp>::value &&
 292                             __well_formed_deleter<_Dp, _Yp*>::value;
 293 };
 294
 295 template <class _Dp>
 296 using __shared_ptr_nullptr_deleter_ctor_reqs = _And<is_move_constructible<_Dp>, __well_formed_deleter<_Dp, nullptr_t> >;
 297
 298 #if defined(_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI)
 299 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI __attribute__((__trivial_abi__))
 300 #else
 301 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI
 302 #endif
 303
 304 template <class _Tp>
 305 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS shared_ptr {
 306   struct __nullptr_sfinae_tag {};
 307
 308 public:
 309 #if _LIBCPP_STD_VER >= 17
 310   typedef weak_ptr<_Tp> weak_type;
 311   typedef remove_extent_t<_Tp> element_type;
 312 #else
 313   typedef _Tp element_type;
 314 #endif
 315
 316   // A shared_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
 317   // any bookkeeping, so it's always trivially relocatable.
 318   using __trivially_relocatable = shared_ptr;
 319
 320 private:
 321   element_type* __ptr_;
 322   __shared_weak_count* __cntrl_;
 323
 324 public:
 325   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
 326
 327   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr(nullptr_t) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
 328
 329   template <class _Yp,
 330             __enable_if_t< _And< __raw_pointer_compatible_with<_Yp, _Tp>
 331   // In C++03 we get errors when trying to do SFINAE with the
 332   // delete operator, so we always pretend that it's deletable.
 333   // The same happens on GCC.
 334 #if !defined(_LIBCPP_CXX03_LANG) && !defined(_LIBCPP_COMPILER_GCC)
 335                                  ,
 336                                  _If<is_array<_Tp>::value, __is_array_deletable<_Yp*>, __is_deletable<_Yp*> >
 337 #endif
 338                                  >::value,
 339                            int> = 0>
 340   _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(_Yp* __p) : __ptr_(__p) {
 341     unique_ptr<_Yp> __hold(__p);
 342     typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 343     typedef __shared_ptr_pointer<_Yp*, __shared_ptr_default_delete<_Tp, _Yp>, _AllocT> _CntrlBlk;
 344     __cntrl_ = new _CntrlBlk(__p, __shared_ptr_default_delete<_Tp, _Yp>(), _AllocT());
 345     __hold.release();
 346     __enable_weak_this(__p, __p);
 347   }
 348
 349   template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
 350   _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d) : __ptr_(__p) {
 351 #if _LIBCPP_HAS_EXCEPTIONS
 352     try {
 353 #endif // _LIBCPP_HAS_EXCEPTIONS
 354       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 355       typedef __shared_ptr_pointer<_Yp*, _Dp, _AllocT> _CntrlBlk;
 356 #ifndef _LIBCPP_CXX03_LANG
 357       __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
 358 #else
 359     __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
 360 #endif // not _LIBCPP_CXX03_LANG
 361       __enable_weak_this(__p, __p);
 362 #if _LIBCPP_HAS_EXCEPTIONS
 363     } catch (...) {
 364       __d(__p);
 365       throw;
 366     }
 367 #endif // _LIBCPP_HAS_EXCEPTIONS
 368   }
 369
 370   template <class _Yp,
 371             class _Dp,
 372             class _Alloc,
 373             __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
 374   _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d, _Alloc __a) : __ptr_(__p) {
 375 #if _LIBCPP_HAS_EXCEPTIONS
 376     try {
 377 #endif // _LIBCPP_HAS_EXCEPTIONS
 378       typedef __shared_ptr_pointer<_Yp*, _Dp, _Alloc> _CntrlBlk;
 379       typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
 380       typedef __allocator_destructor<_A2> _D2;
 381       _A2 __a2(__a);
 382       unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
 383       ::new ((void*)std::addressof(*__hold2.get()))
 384 #ifndef _LIBCPP_CXX03_LANG
 385           _CntrlBlk(__p, std::move(__d), __a);
 386 #else
 387         _CntrlBlk(__p, __d, __a);
 388 #endif // not _LIBCPP_CXX03_LANG
 389       __cntrl_ = std::addressof(*__hold2.release());
 390       __enable_weak_this(__p, __p);
 391 #if _LIBCPP_HAS_EXCEPTIONS
 392     } catch (...) {
 393       __d(__p);
 394       throw;
 395     }
 396 #endif // _LIBCPP_HAS_EXCEPTIONS
 397   }
 398
 399   template <class _Dp>
 400   _LIBCPP_HIDE_FROM_ABI shared_ptr(
 401       nullptr_t __p,
 402       _Dp __d,
 403       __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs<_Dp>::value, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
 404       : __ptr_(nullptr) {
 405 #if _LIBCPP_HAS_EXCEPTIONS
 406     try {
 407 #endif // _LIBCPP_HAS_EXCEPTIONS
 408       typedef typename __shared_ptr_default_allocator<_Tp>::type _AllocT;
 409       typedef __shared_ptr_pointer<nullptr_t, _Dp, _AllocT> _CntrlBlk;
 410 #ifndef _LIBCPP_CXX03_LANG
 411       __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
 412 #else
 413     __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
 414 #endif // not _LIBCPP_CXX03_LANG
 415 #if _LIBCPP_HAS_EXCEPTIONS
 416     } catch (...) {
 417       __d(__p);
 418       throw;
 419     }
 420 #endif // _LIBCPP_HAS_EXCEPTIONS
 421   }
 422
 423   template <class _Dp, class _Alloc>
 424   _LIBCPP_HIDE_FROM_ABI shared_ptr(
 425       nullptr_t __p,
 426       _Dp __d,
 427       _Alloc __a,
 428       __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs<_Dp>::value, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
 429       : __ptr_(nullptr) {
 430 #if _LIBCPP_HAS_EXCEPTIONS
 431     try {
 432 #endif // _LIBCPP_HAS_EXCEPTIONS
 433       typedef __shared_ptr_pointer<nullptr_t, _Dp, _Alloc> _CntrlBlk;
 434       typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
 435       typedef __allocator_destructor<_A2> _D2;
 436       _A2 __a2(__a);
 437       unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
 438       ::new ((void*)std::addressof(*__hold2.get()))
 439 #ifndef _LIBCPP_CXX03_LANG
 440           _CntrlBlk(__p, std::move(__d), __a);
 441 #else
 442         _CntrlBlk(__p, __d, __a);
 443 #endif // not _LIBCPP_CXX03_LANG
 444       __cntrl_ = std::addressof(*__hold2.release());
 445 #if _LIBCPP_HAS_EXCEPTIONS
 446     } catch (...) {
 447       __d(__p);
 448       throw;
 449     }
 450 #endif // _LIBCPP_HAS_EXCEPTIONS
 451   }
 452
 453   template <class _Yp>
 454   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) _NOEXCEPT
 455       : __ptr_(__p),
 456         __cntrl_(__r.__cntrl_) {
 457     if (__cntrl_)
 458       __cntrl_->__add_shared();
 459   }
 460
 461 // LWG-2996
 462 // We don't backport because it is an evolutionary change.
 463 #if _LIBCPP_STD_VER >= 20
 464   template <class _Yp>
 465   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
 466       : __ptr_(__p), __cntrl_(__r.__cntrl_) {
 467     __r.__ptr_   = nullptr;
 468     __r.__cntrl_ = nullptr;
 469   }
 470 #endif
 471
 472   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
 473     if (__cntrl_)
 474       __cntrl_->__add_shared();
 475   }
 476
 477   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 478   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
 479     if (__cntrl_)
 480       __cntrl_->__add_shared();
 481   }
 482
 483   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
 484     __r.__ptr_   = nullptr;
 485     __r.__cntrl_ = nullptr;
 486   }
 487
 488   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 489   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
 490     __r.__ptr_   = nullptr;
 491     __r.__cntrl_ = nullptr;
 492   }
 493
 494   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 495   _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(const weak_ptr<_Yp>& __r)
 496       : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_ ? __r.__cntrl_->lock() : __r.__cntrl_) {
 497     if (__cntrl_ == nullptr)
 498       __throw_bad_weak_ptr();
 499   }
 500
 501 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
 502   template <class _Yp, __enable_if_t<is_convertible<_Yp*, element_type*>::value, int> = 0>
 503   _LIBCPP_HIDE_FROM_ABI shared_ptr(auto_ptr<_Yp>&& __r) : __ptr_(__r.get()) {
 504     typedef __shared_ptr_pointer<_Yp*, default_delete<_Yp>, allocator<__remove_cv_t<_Yp> > > _CntrlBlk;
 505     __cntrl_ = new _CntrlBlk(__r.get(), default_delete<_Yp>(), allocator<__remove_cv_t<_Yp> >());
 506     __enable_weak_this(__r.get(), __r.get());
 507     __r.release();
 508   }
 509 #endif
 510
 511   template <class _Yp,
 512             class _Dp,
 513             __enable_if_t<!is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
 514                               is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
 515                           int> = 0>
 516   _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
 517 #if _LIBCPP_STD_VER >= 14
 518     if (__ptr_ == nullptr)
 519       __cntrl_ = nullptr;
 520     else
 521 #endif
 522     {
 523       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 524       typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer, _Dp, _AllocT> _CntrlBlk;
 525       __cntrl_ = new _CntrlBlk(__r.get(), std::move(__r.get_deleter()), _AllocT());
 526       __enable_weak_this(__r.get(), __r.get());
 527     }
 528     __r.release();
 529   }
 530
 531   template <class _Yp,
 532             class _Dp,
 533             class              = void,
 534             __enable_if_t<is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
 535                               is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
 536                           int> = 0>
 537   _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
 538 #if _LIBCPP_STD_VER >= 14
 539     if (__ptr_ == nullptr)
 540       __cntrl_ = nullptr;
 541     else
 542 #endif
 543     {
 544       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 545       typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer,
 546                                    reference_wrapper<__libcpp_remove_reference_t<_Dp> >,
 547                                    _AllocT>
 548           _CntrlBlk;
 549       __cntrl_ = new _CntrlBlk(__r.get(), std::ref(__r.get_deleter()), _AllocT());
 550       __enable_weak_this(__r.get(), __r.get());
 551     }
 552     __r.release();
 553   }
 554
 555   _LIBCPP_HIDE_FROM_ABI ~shared_ptr() {
 556     if (__cntrl_)
 557       __cntrl_->__release_shared();
 558   }
 559
 560   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr& __r) _NOEXCEPT {
 561     shared_ptr(__r).swap(*this);
 562     return *this;
 563   }
 564
 565   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 566   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr<_Yp>& __r) _NOEXCEPT {
 567     shared_ptr(__r).swap(*this);
 568     return *this;
 569   }
 570
 571   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr&& __r) _NOEXCEPT {
 572     shared_ptr(std::move(__r)).swap(*this);
 573     return *this;
 574   }
 575
 576   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 577   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr<_Yp>&& __r) {
 578     shared_ptr(std::move(__r)).swap(*this);
 579     return *this;
 580   }
 581
 582 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
 583   template <class _Yp,
 584             __enable_if_t<!is_array<_Yp>::value && is_convertible<_Yp*, typename shared_ptr<_Tp>::element_type*>::value,
 585                           int> = 0>
 586   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(auto_ptr<_Yp>&& __r) {
 587     shared_ptr(std::move(__r)).swap(*this);
 588     return *this;
 589   }
 590 #endif
 591
 592   template <class _Yp,
 593             class _Dp,
 594             __enable_if_t<_And< __compatible_with<_Yp, _Tp>,
 595                                 is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*> >::value,
 596                           int> = 0>
 597   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(unique_ptr<_Yp, _Dp>&& __r) {
 598     shared_ptr(std::move(__r)).swap(*this);
 599     return *this;
 600   }
 601
 602   _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr& __r) _NOEXCEPT {
 603     std::swap(__ptr_, __r.__ptr_);
 604     std::swap(__cntrl_, __r.__cntrl_);
 605   }
 606
 607   _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT { shared_ptr().swap(*this); }
 608
 609   template <class _Yp, __enable_if_t<__raw_pointer_compatible_with<_Yp, _Tp>::value, int> = 0>
 610   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p) {
 611     shared_ptr(__p).swap(*this);
 612   }
 613
 614   template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
 615   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d) {
 616     shared_ptr(__p, __d).swap(*this);
 617   }
 618
 619   template <class _Yp,
 620             class _Dp,
 621             class _Alloc,
 622             __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
 623   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d, _Alloc __a) {
 624     shared_ptr(__p, __d, __a).swap(*this);
 625   }
 626
 627   _LIBCPP_HIDE_FROM_ABI element_type* get() const _NOEXCEPT { return __ptr_; }
 628
 629   _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator*() const _NOEXCEPT { return *__ptr_; }
 630
 631   _LIBCPP_HIDE_FROM_ABI element_type* operator->() const _NOEXCEPT {
 632     static_assert(!is_array<_Tp>::value, "std::shared_ptr<T>::operator-> is only valid when T is not an array type.");
 633     return __ptr_;
 634   }
 635
 636   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __cntrl_ ? __cntrl_->use_count() : 0; }
 637
 638 #if _LIBCPP_STD_VER < 20 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_SHARED_PTR_UNIQUE)
 639   _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI bool unique() const _NOEXCEPT { return use_count() == 1; }
 640 #endif
 641
 642   _LIBCPP_HIDE_FROM_ABI explicit operator bool() const _NOEXCEPT { return get() != nullptr; }
 643
 644   template <class _Up>
 645   _LIBCPP_HIDE_FROM_ABI bool owner_before(shared_ptr<_Up> const& __p) const _NOEXCEPT {
 646     return __cntrl_ < __p.__cntrl_;
 647   }
 648
 649   template <class _Up>
 650   _LIBCPP_HIDE_FROM_ABI bool owner_before(weak_ptr<_Up> const& __p) const _NOEXCEPT {
 651     return __cntrl_ < __p.__cntrl_;
 652   }
 653
 654   _LIBCPP_HIDE_FROM_ABI bool __owner_equivalent(const shared_ptr& __p) const { return __cntrl_ == __p.__cntrl_; }
 655
 656 #if _LIBCPP_STD_VER >= 17
 657   _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator[](ptrdiff_t __i) const {
 658     static_assert(is_array<_Tp>::value, "std::shared_ptr<T>::operator[] is only valid when T is an array type.");
 659     return __ptr_[__i];
 660   }
 661 #endif
 662
 663 #if _LIBCPP_HAS_RTTI
 664   template <class _Dp>
 665   _LIBCPP_HIDE_FROM_ABI _Dp* __get_deleter() const _NOEXCEPT {
 666     return static_cast<_Dp*>(__cntrl_ ? const_cast<void*>(__cntrl_->__get_deleter(typeid(_Dp))) : nullptr);
 667   }
 668 #endif // _LIBCPP_HAS_RTTI
 669
 670   template <class _Yp, class _CntrlBlk>
 671   _LIBCPP_HIDE_FROM_ABI static shared_ptr<_Tp> __create_with_control_block(_Yp* __p, _CntrlBlk* __cntrl) _NOEXCEPT {
 672     shared_ptr<_Tp> __r;
 673     __r.__ptr_   = __p;
 674     __r.__cntrl_ = __cntrl;
 675     __r.__enable_weak_this(__r.__ptr_, __r.__ptr_);
 676     return __r;
 677   }
 678
 679 private:
 680   template <class _Yp, bool = is_function<_Yp>::value>
 681   struct __shared_ptr_default_allocator {
 682     typedef allocator<__remove_cv_t<_Yp> > type;
 683   };
 684
 685   template <class _Yp>
 686   struct __shared_ptr_default_allocator<_Yp, true> {
 687     typedef allocator<__shared_ptr_dummy_rebind_allocator_type> type;
 688   };
 689
 690   template <class _Yp,
 691             class _OrigPtr,
 692             __enable_if_t<is_convertible<_OrigPtr*, const enable_shared_from_this<_Yp>*>::value, int> = 0>
 693   _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(const enable_shared_from_this<_Yp>* __e, _OrigPtr* __ptr) _NOEXCEPT {
 694     typedef __remove_cv_t<_Yp> _RawYp;
 695     if (__e && __e->__weak_this_.expired()) {
 696       __e->__weak_this_ = shared_ptr<_RawYp>(*this, const_cast<_RawYp*>(static_cast<const _Yp*>(__ptr)));
 697     }
 698   }
 699
 700   _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(...) _NOEXCEPT {}
 701
 702   template <class, class _Yp>
 703   struct __shared_ptr_default_delete : default_delete<_Yp> {};
 704
 705   template <class _Yp, class _Un, size_t _Sz>
 706   struct __shared_ptr_default_delete<_Yp[_Sz], _Un> : default_delete<_Yp[]> {};
 707
 708   template <class _Yp, class _Un>
 709   struct __shared_ptr_default_delete<_Yp[], _Un> : default_delete<_Yp[]> {};
 710
 711   template <class _Up>
 712   friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
 713   template <class _Up>
 714   friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
 715 };
 716
 717 #if _LIBCPP_STD_VER >= 17
 718 template <class _Tp>
 719 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
 720 template <class _Tp, class _Dp>
 721 shared_ptr(unique_ptr<_Tp, _Dp>) -> shared_ptr<_Tp>;
 722 #endif
 723
 724 //
 725 // std::allocate_shared and std::make_shared
 726 //
 727 template <class _Tp, class _Alloc, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 728 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, _Args&&... __args) {
 729   using _ControlBlock          = __shared_ptr_emplace<_Tp, _Alloc>;
 730   using _ControlBlockAllocator = typename __allocator_traits_rebind<_Alloc, _ControlBlock>::type;
 731   __allocation_guard<_ControlBlockAllocator> __guard(__a, 1);
 732   ::new ((void*)std::addressof(*__guard.__get())) _ControlBlock(__a, std::forward<_Args>(__args)...);
 733   auto __control_block = __guard.__release_ptr();
 734   return shared_ptr<_Tp>::__create_with_control_block(
 735       (*__control_block).__get_elem(), std::addressof(*__control_block));
 736 }
 737
 738 template <class _Tp, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 739 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(_Args&&... __args) {
 740   return std::allocate_shared<_Tp>(allocator<__remove_cv_t<_Tp> >(), std::forward<_Args>(__args)...);
 741 }
 742
 743 #if _LIBCPP_STD_VER >= 20
 744
 745 template <class _Tp, class _Alloc, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 746 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
 747   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
 748   _ForOverwriteAllocator __alloc(__a);
 749   return std::allocate_shared<_Tp>(__alloc);
 750 }
 751
 752 template <class _Tp, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 753 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
 754   return std::allocate_shared_for_overwrite<_Tp>(allocator<__remove_cv_t<_Tp>>());
 755 }
 756
 757 #endif // _LIBCPP_STD_VER >= 20
 758
 759 #if _LIBCPP_STD_VER >= 17
 760
 761 template <size_t _Alignment>
 762 struct __sp_aligned_storage {
 763   alignas(_Alignment) char __storage[_Alignment];
 764 };
 765
 766 template <class _Tp, class _Alloc>
 767 struct __unbounded_array_control_block;
 768
 769 template <class _Tp, class _Alloc>
 770 struct __unbounded_array_control_block<_Tp[], _Alloc> : __shared_weak_count {
 771   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }
 772
 773   _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(
 774       _Alloc const& __alloc, size_t __count, _Tp const& __arg)
 775       : __alloc_(__alloc), __count_(__count) {
 776     std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::begin(__data_), __count_, __arg);
 777   }
 778
 779   _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(_Alloc const& __alloc, size_t __count)
 780       : __alloc_(__alloc), __count_(__count) {
 781 #  if _LIBCPP_STD_VER >= 20
 782     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
 783       // We are purposefully not using an allocator-aware default construction because the spec says so.
 784       // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
 785       std::uninitialized_default_construct_n(std::begin(__data_), __count_);
 786     } else {
 787       std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
 788     }
 789 #  else
 790     std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
 791 #  endif
 792   }
 793
 794   // Returns the number of bytes required to store a control block followed by the given number
 795   // of elements of _Tp, with the whole storage being aligned to a multiple of _Tp's alignment.
 796   _LIBCPP_HIDE_FROM_ABI static constexpr size_t __bytes_for(size_t __elements) {
 797     // When there's 0 elements, the control block alone is enough since it holds one element.
 798     // Otherwise, we allocate one fewer element than requested because the control block already
 799     // holds one. Also, we use the bitwise formula below to ensure that we allocate enough bytes
 800     // for the whole allocation to be a multiple of _Tp's alignment. That formula is taken from [1].
 801     //
 802     // [1]: https://en.wikipedia.org/wiki/Data_structure_alignment#Computing_padding
 803     size_t __bytes           = __elements == 0 ? sizeof(__unbounded_array_control_block)
 804                                                : (__elements - 1) * sizeof(_Tp) + sizeof(__unbounded_array_control_block);
 805     constexpr size_t __align = alignof(_Tp);
 806     return (__bytes + __align - 1) & ~(__align - 1);
 807   }
 808
 809   _LIBCPP_HIDE_FROM_ABI_VIRTUAL
 810   ~__unbounded_array_control_block() override {
 811   } // can't be `= default` because of the sometimes-non-trivial union member __data_
 812
 813 private:
 814   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
 815 #  if _LIBCPP_STD_VER >= 20
 816     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
 817       std::__reverse_destroy(__data_, __data_ + __count_);
 818     } else {
 819       __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
 820       std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
 821     }
 822 #  else
 823     __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
 824     std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
 825 #  endif
 826   }
 827
 828   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
 829     using _AlignedStorage = __sp_aligned_storage<alignof(__unbounded_array_control_block)>;
 830     using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
 831     using _PointerTraits  = pointer_traits<typename allocator_traits<_StorageAlloc>::pointer>;
 832
 833     _StorageAlloc __tmp(__alloc_);
 834     __alloc_.~_Alloc();
 835     size_t __size              = __unbounded_array_control_block::__bytes_for(__count_);
 836     _AlignedStorage* __storage = reinterpret_cast<_AlignedStorage*>(this);
 837     allocator_traits<_StorageAlloc>::deallocate(
 838         __tmp, _PointerTraits::pointer_to(*__storage), __size / sizeof(_AlignedStorage));
 839   }
 840
 841   _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
 842   size_t __count_;
 843   union {
 844     _Tp __data_[1];
 845   };
 846 };
 847
 848 template <class _Array, class _Alloc, class... _Arg>
 849 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Array>
 850 __allocate_shared_unbounded_array(const _Alloc& __a, size_t __n, _Arg&&... __arg) {
 851   static_assert(__is_unbounded_array_v<_Array>);
 852   // We compute the number of bytes necessary to hold the control block and the
 853   // array elements. Then, we allocate an array of properly-aligned dummy structs
 854   // large enough to hold the control block and array. This allows shifting the
 855   // burden of aligning memory properly from us to the allocator.
 856   using _ControlBlock   = __unbounded_array_control_block<_Array, _Alloc>;
 857   using _AlignedStorage = __sp_aligned_storage<alignof(_ControlBlock)>;
 858   using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
 859   __allocation_guard<_StorageAlloc> __guard(__a, _ControlBlock::__bytes_for(__n) / sizeof(_AlignedStorage));
 860   _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
 861   std::__construct_at(__control_block, __a, __n, std::forward<_Arg>(__arg)...);
 862   __guard.__release_ptr();
 863   return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
 864 }
 865
 866 template <class _Tp, class _Alloc>
 867 struct __bounded_array_control_block;
 868
 869 template <class _Tp, size_t _Count, class _Alloc>
 870 struct __bounded_array_control_block<_Tp[_Count], _Alloc> : __shared_weak_count {
 871   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }
 872
 873   _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc, _Tp const& __arg)
 874       : __alloc_(__alloc) {
 875     std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count, __arg);
 876   }
 877
 878   _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc) : __alloc_(__alloc) {
 879 #  if _LIBCPP_STD_VER >= 20
 880     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
 881       // We are purposefully not using an allocator-aware default construction because the spec says so.
 882       // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
 883       std::uninitialized_default_construct_n(std::addressof(__data_[0]), _Count);
 884     } else {
 885       std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
 886     }
 887 #  else
 888     std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
 889 #  endif
 890   }
 891
 892   _LIBCPP_HIDE_FROM_ABI_VIRTUAL
 893   ~__bounded_array_control_block() override {
 894   } // can't be `= default` because of the sometimes-non-trivial union member __data_
 895
 896 private:
 897   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
 898 #  if _LIBCPP_STD_VER >= 20
 899     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
 900       std::__reverse_destroy(__data_, __data_ + _Count);
 901     } else {
 902       __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
 903       std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
 904     }
 905 #  else
 906     __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
 907     std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
 908 #  endif
 909   }
 910
 911   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
 912     using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, __bounded_array_control_block>;
 913     using _PointerTraits     = pointer_traits<typename allocator_traits<_ControlBlockAlloc>::pointer>;
 914
 915     _ControlBlockAlloc __tmp(__alloc_);
 916     __alloc_.~_Alloc();
 917     allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, _PointerTraits::pointer_to(*this), 1);
 918   }
 919
 920   _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
 921   union {
 922     _Tp __data_[_Count];
 923   };
 924 };
 925
 926 template <class _Array, class _Alloc, class... _Arg>
 927 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Array> __allocate_shared_bounded_array(const _Alloc& __a, _Arg&&... __arg) {
 928   static_assert(__is_bounded_array_v<_Array>);
 929   using _ControlBlock      = __bounded_array_control_block<_Array, _Alloc>;
 930   using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, _ControlBlock>;
 931
 932   __allocation_guard<_ControlBlockAlloc> __guard(__a, 1);
 933   _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
 934   std::__construct_at(__control_block, __a, std::forward<_Arg>(__arg)...);
 935   __guard.__release_ptr();
 936   return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
 937 }
 938
 939 #endif // _LIBCPP_STD_VER >= 17
 940
 941 #if _LIBCPP_STD_VER >= 20
 942
 943 // bounded array variants
 944 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 945 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a) {
 946   return std::__allocate_shared_bounded_array<_Tp>(__a);
 947 }
 948
 949 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 950 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, const remove_extent_t<_Tp>& __u) {
 951   return std::__allocate_shared_bounded_array<_Tp>(__a, __u);
 952 }
 953
 954 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 955 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
 956   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
 957   _ForOverwriteAllocator __alloc(__a);
 958   return std::__allocate_shared_bounded_array<_Tp>(__alloc);
 959 }
 960
 961 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 962 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared() {
 963   return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>());
 964 }
 965
 966 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 967 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(const remove_extent_t<_Tp>& __u) {
 968   return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>(), __u);
 969 }
 970
 971 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 972 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
 973   return std::__allocate_shared_bounded_array<_Tp>(allocator<__for_overwrite_tag>());
 974 }
 975
 976 // unbounded array variants
 977 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 978 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n) {
 979   return std::__allocate_shared_unbounded_array<_Tp>(__a, __n);
 980 }
 981
 982 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 983 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n, const remove_extent_t<_Tp>& __u) {
 984   return std::__allocate_shared_unbounded_array<_Tp>(__a, __n, __u);
 985 }
 986
 987 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 988 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a, size_t __n) {
 989   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
 990   _ForOverwriteAllocator __alloc(__a);
 991   return std::__allocate_shared_unbounded_array<_Tp>(__alloc, __n);
 992 }
 993
 994 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 995 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n) {
 996   return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n);
 997 }
 998
 999 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1000 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n, const remove_extent_t<_Tp>& __u) {
1001   return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n, __u);
1002 }
1003
1004 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1005 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite(size_t __n) {
1006   return std::__allocate_shared_unbounded_array<_Tp>(allocator<__for_overwrite_tag>(), __n);
1007 }
1008
1009 #endif // _LIBCPP_STD_VER >= 20
1010
1011 template <class _Tp, class _Up>
1012 inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1013   return __x.get() == __y.get();
1014 }
1015
1016 #if _LIBCPP_STD_VER <= 17
1017
1018 template <class _Tp, class _Up>
1019 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1020   return !(__x == __y);
1021 }
1022
1023 template <class _Tp, class _Up>
1024 inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1025 #  if _LIBCPP_STD_VER <= 11
1026   typedef typename common_type<_Tp*, _Up*>::type _Vp;
1027   return less<_Vp>()(__x.get(), __y.get());
1028 #  else
1029   return less<>()(__x.get(), __y.get());
1030 #  endif
1031 }
1032
1033 template <class _Tp, class _Up>
1034 inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1035   return __y < __x;
1036 }
1037
1038 template <class _Tp, class _Up>
1039 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1040   return !(__y < __x);
1041 }
1042
1043 template <class _Tp, class _Up>
1044 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1045   return !(__x < __y);
1046 }
1047
1048 #endif // _LIBCPP_STD_VER <= 17
1049
1050 #if _LIBCPP_STD_VER >= 20
1051 template <class _Tp, class _Up>
1052 _LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) noexcept {
1053   return compare_three_way()(__x.get(), __y.get());
1054 }
1055 #endif
1056
1057 template <class _Tp>
1058 inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1059   return !__x;
1060 }
1061
1062 #if _LIBCPP_STD_VER <= 17
1063
1064 template <class _Tp>
1065 inline _LIBCPP_HIDE_FROM_ABI bool operator==(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1066   return !__x;
1067 }
1068
1069 template <class _Tp>
1070 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1071   return static_cast<bool>(__x);
1072 }
1073
1074 template <class _Tp>
1075 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1076   return static_cast<bool>(__x);
1077 }
1078
1079 template <class _Tp>
1080 inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1081   return less<typename shared_ptr<_Tp>::element_type*>()(__x.get(), nullptr);
1082 }
1083
1084 template <class _Tp>
1085 inline _LIBCPP_HIDE_FROM_ABI bool operator<(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1086   return less<typename shared_ptr<_Tp>::element_type*>()(nullptr, __x.get());
1087 }
1088
1089 template <class _Tp>
1090 inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1091   return nullptr < __x;
1092 }
1093
1094 template <class _Tp>
1095 inline _LIBCPP_HIDE_FROM_ABI bool operator>(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1096   return __x < nullptr;
1097 }
1098
1099 template <class _Tp>
1100 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1101   return !(nullptr < __x);
1102 }
1103
1104 template <class _Tp>
1105 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1106   return !(__x < nullptr);
1107 }
1108
1109 template <class _Tp>
1110 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1111   return !(__x < nullptr);
1112 }
1113
1114 template <class _Tp>
1115 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1116   return !(nullptr < __x);
1117 }
1118
1119 #endif // _LIBCPP_STD_VER <= 17
1120
1121 #if _LIBCPP_STD_VER >= 20
1122 template <class _Tp>
1123 _LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, nullptr_t) noexcept {
1124   return compare_three_way()(__x.get(), static_cast<typename shared_ptr<_Tp>::element_type*>(nullptr));
1125 }
1126 #endif
1127
1128 template <class _Tp>
1129 inline _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr<_Tp>& __x, shared_ptr<_Tp>& __y) _NOEXCEPT {
1130   __x.swap(__y);
1131 }
1132
1133 template <class _Tp, class _Up>
1134 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1135   return shared_ptr<_Tp>(__r, static_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
1136 }
1137
1138 // LWG-2996
1139 // We don't backport because it is an evolutionary change.
1140 #if _LIBCPP_STD_VER >= 20
1141 template <class _Tp, class _Up>
1142 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1143   return shared_ptr<_Tp>(std::move(__r), static_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1144 }
1145 #endif
1146
1147 template <class _Tp, class _Up>
1148 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1149   typedef typename shared_ptr<_Tp>::element_type _ET;
1150   _ET* __p = dynamic_cast<_ET*>(__r.get());
1151   return __p ? shared_ptr<_Tp>(__r, __p) : shared_ptr<_Tp>();
1152 }
1153
1154 // LWG-2996
1155 // We don't backport because it is an evolutionary change.
1156 #if _LIBCPP_STD_VER >= 20
1157 template <class _Tp, class _Up>
1158 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1159   auto* __p = dynamic_cast<typename shared_ptr<_Tp>::element_type*>(__r.get());
1160   return __p ? shared_ptr<_Tp>(std::move(__r), __p) : shared_ptr<_Tp>();
1161 }
1162 #endif
1163
1164 template <class _Tp, class _Up>
1165 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1166   typedef typename shared_ptr<_Tp>::element_type _RTp;
1167   return shared_ptr<_Tp>(__r, const_cast<_RTp*>(__r.get()));
1168 }
1169
1170 // LWG-2996
1171 // We don't backport because it is an evolutionary change.
1172 #if _LIBCPP_STD_VER >= 20
1173 template <class _Tp, class _Up>
1174 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1175   return shared_ptr<_Tp>(std::move(__r), const_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1176 }
1177 #endif
1178
1179 template <class _Tp, class _Up>
1180 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1181   return shared_ptr<_Tp>(__r, reinterpret_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
1182 }
1183
1184 // LWG-2996
1185 // We don't backport because it is an evolutionary change.
1186 #if _LIBCPP_STD_VER >= 20
1187 template <class _Tp, class _Up>
1188 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1189   return shared_ptr<_Tp>(std::move(__r), reinterpret_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1190 }
1191 #endif
1192
1193 #if _LIBCPP_HAS_RTTI
1194
1195 template <class _Dp, class _Tp>
1196 inline _LIBCPP_HIDE_FROM_ABI _Dp* get_deleter(const shared_ptr<_Tp>& __p) _NOEXCEPT {
1197   return __p.template __get_deleter<_Dp>();
1198 }
1199
1200 #endif // _LIBCPP_HAS_RTTI
1201
1202 template <class _Tp>
1203 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS weak_ptr {
1204 public:
1205 #if _LIBCPP_STD_VER >= 17
1206   typedef remove_extent_t<_Tp> element_type;
1207 #else
1208   typedef _Tp element_type;
1209 #endif
1210
1211   // A weak_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
1212   // any bookkeeping, so it's always trivially relocatable.
1213   using __trivially_relocatable = weak_ptr;
1214
1215 private:
1216   element_type* __ptr_;
1217   __shared_weak_count* __cntrl_;
1218
1219 public:
1220   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR weak_ptr() _NOEXCEPT;
1221
1222   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1223   _LIBCPP_HIDE_FROM_ABI weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT;
1224
1225   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr const& __r) _NOEXCEPT;
1226
1227   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1228   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT;
1229
1230   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr&& __r) _NOEXCEPT;
1231
1232   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1233   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT;
1234
1235   _LIBCPP_HIDE_FROM_ABI ~weak_ptr();
1236
1237   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr const& __r) _NOEXCEPT;
1238   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1239   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT;
1240
1241   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr&& __r) _NOEXCEPT;
1242   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1243   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT;
1244
1245   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1246   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT;
1247
1248   _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr& __r) _NOEXCEPT;
1249   _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT;
1250
1251   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __cntrl_ ? __cntrl_->use_count() : 0; }
1252   _LIBCPP_HIDE_FROM_ABI bool expired() const _NOEXCEPT { return __cntrl_ == nullptr || __cntrl_->use_count() == 0; }
1253   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> lock() const _NOEXCEPT;
1254   template <class _Up>
1255   _LIBCPP_HIDE_FROM_ABI bool owner_before(const shared_ptr<_Up>& __r) const _NOEXCEPT {
1256     return __cntrl_ < __r.__cntrl_;
1257   }
1258   template <class _Up>
1259   _LIBCPP_HIDE_FROM_ABI bool owner_before(const weak_ptr<_Up>& __r) const _NOEXCEPT {
1260     return __cntrl_ < __r.__cntrl_;
1261   }
1262
1263   template <class _Up>
1264   friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
1265   template <class _Up>
1266   friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
1267 };
1268
1269 #if _LIBCPP_STD_VER >= 17
1270 template <class _Tp>
1271 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
1272 #endif
1273
1274 template <class _Tp>
1275 inline _LIBCPP_CONSTEXPR weak_ptr<_Tp>::weak_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
1276
1277 template <class _Tp>
1278 inline weak_ptr<_Tp>::weak_ptr(weak_ptr const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
1279   if (__cntrl_)
1280     __cntrl_->__add_weak();
1281 }
1282
1283 template <class _Tp>
1284 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1285 inline weak_ptr<_Tp>::weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
1286   if (__cntrl_)
1287     __cntrl_->__add_weak();
1288 }
1289
1290 template <class _Tp>
1291 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1292 inline weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
1293   shared_ptr<_Yp> __s = __r.lock();
1294   *this               = weak_ptr<_Tp>(__s);
1295 }
1296
1297 template <class _Tp>
1298 inline weak_ptr<_Tp>::weak_ptr(weak_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
1299   __r.__ptr_   = nullptr;
1300   __r.__cntrl_ = nullptr;
1301 }
1302
1303 template <class _Tp>
1304 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1305 inline weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
1306   shared_ptr<_Yp> __s = __r.lock();
1307   *this               = weak_ptr<_Tp>(__s);
1308   __r.reset();
1309 }
1310
1311 template <class _Tp>
1312 weak_ptr<_Tp>::~weak_ptr() {
1313   if (__cntrl_)
1314     __cntrl_->__release_weak();
1315 }
1316
1317 template <class _Tp>
1318 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr const& __r) _NOEXCEPT {
1319   weak_ptr(__r).swap(*this);
1320   return *this;
1321 }
1322
1323 template <class _Tp>
1324 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1325 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT {
1326   weak_ptr(__r).swap(*this);
1327   return *this;
1328 }
1329
1330 template <class _Tp>
1331 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr&& __r) _NOEXCEPT {
1332   weak_ptr(std::move(__r)).swap(*this);
1333   return *this;
1334 }
1335
1336 template <class _Tp>
1337 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1338 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT {
1339   weak_ptr(std::move(__r)).swap(*this);
1340   return *this;
1341 }
1342
1343 template <class _Tp>
1344 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1345 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT {
1346   weak_ptr(__r).swap(*this);
1347   return *this;
1348 }
1349
1350 template <class _Tp>
1351 inline void weak_ptr<_Tp>::swap(weak_ptr& __r) _NOEXCEPT {
1352   std::swap(__ptr_, __r.__ptr_);
1353   std::swap(__cntrl_, __r.__cntrl_);
1354 }
1355
1356 template <class _Tp>
1357 inline _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr<_Tp>& __x, weak_ptr<_Tp>& __y) _NOEXCEPT {
1358   __x.swap(__y);
1359 }
1360
1361 template <class _Tp>
1362 inline void weak_ptr<_Tp>::reset() _NOEXCEPT {
1363   weak_ptr().swap(*this);
1364 }
1365
1366 template <class _Tp>
1367 shared_ptr<_Tp> weak_ptr<_Tp>::lock() const _NOEXCEPT {
1368   shared_ptr<_Tp> __r;
1369   __r.__cntrl_ = __cntrl_ ? __cntrl_->lock() : __cntrl_;
1370   if (__r.__cntrl_)
1371     __r.__ptr_ = __ptr_;
1372   return __r;
1373 }
1374
1375 #if _LIBCPP_STD_VER >= 17
1376 template <class _Tp = void>
1377 struct owner_less;
1378 #else
1379 template <class _Tp>
1380 struct owner_less;
1381 #endif
1382
1383 template <class _Tp>
1384 struct _LIBCPP_TEMPLATE_VIS owner_less<shared_ptr<_Tp> > : __binary_function<shared_ptr<_Tp>, shared_ptr<_Tp>, bool> {
1385   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
1386     return __x.owner_before(__y);
1387   }
1388   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
1389     return __x.owner_before(__y);
1390   }
1391   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
1392     return __x.owner_before(__y);
1393   }
1394 };
1395
1396 template <class _Tp>
1397 struct _LIBCPP_TEMPLATE_VIS owner_less<weak_ptr<_Tp> > : __binary_function<weak_ptr<_Tp>, weak_ptr<_Tp>, bool> {
1398   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
1399     return __x.owner_before(__y);
1400   }
1401   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
1402     return __x.owner_before(__y);
1403   }
1404   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
1405     return __x.owner_before(__y);
1406   }
1407 };
1408
1409 #if _LIBCPP_STD_VER >= 17
1410 template <>
1411 struct _LIBCPP_TEMPLATE_VIS owner_less<void> {
1412   template <class _Tp, class _Up>
1413   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
1414     return __x.owner_before(__y);
1415   }
1416   template <class _Tp, class _Up>
1417   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
1418     return __x.owner_before(__y);
1419   }
1420   template <class _Tp, class _Up>
1421   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
1422     return __x.owner_before(__y);
1423   }
1424   template <class _Tp, class _Up>
1425   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
1426     return __x.owner_before(__y);
1427   }
1428   typedef void is_transparent;
1429 };
1430 #endif
1431
1432 template <class _Tp>
1433 class _LIBCPP_TEMPLATE_VIS enable_shared_from_this {
1434   mutable weak_ptr<_Tp> __weak_this_;
1435
1436 protected:
1437   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR enable_shared_from_this() _NOEXCEPT {}
1438   _LIBCPP_HIDE_FROM_ABI enable_shared_from_this(enable_shared_from_this const&) _NOEXCEPT {}
1439   _LIBCPP_HIDE_FROM_ABI enable_shared_from_this& operator=(enable_shared_from_this const&) _NOEXCEPT { return *this; }
1440   _LIBCPP_HIDE_FROM_ABI ~enable_shared_from_this() {}
1441
1442 public:
1443   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> shared_from_this() { return shared_ptr<_Tp>(__weak_this_); }
1444   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp const> shared_from_this() const { return shared_ptr<const _Tp>(__weak_this_); }
1445
1446 #if _LIBCPP_STD_VER >= 17
1447   _LIBCPP_HIDE_FROM_ABI weak_ptr<_Tp> weak_from_this() _NOEXCEPT { return __weak_this_; }
1448
1449   _LIBCPP_HIDE_FROM_ABI weak_ptr<const _Tp> weak_from_this() const _NOEXCEPT { return __weak_this_; }
1450 #endif // _LIBCPP_STD_VER >= 17
1451
1452   template <class _Up>
1453   friend class shared_ptr;
1454 };
1455
1456 template <class _Tp>
1457 struct _LIBCPP_TEMPLATE_VIS hash;
1458
1459 template <class _Tp>
1460 struct _LIBCPP_TEMPLATE_VIS hash<shared_ptr<_Tp> > {
1461 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_BINDER_TYPEDEFS)
1462   _LIBCPP_DEPRECATED_IN_CXX17 typedef shared_ptr<_Tp> argument_type;
1463   _LIBCPP_DEPRECATED_IN_CXX17 typedef size_t result_type;
1464 #endif
1465
1466   _LIBCPP_HIDE_FROM_ABI size_t operator()(const shared_ptr<_Tp>& __ptr) const _NOEXCEPT {
1467     return hash<typename shared_ptr<_Tp>::element_type*>()(__ptr.get());
1468   }
1469 };
1470
1471 template <class _CharT, class _Traits, class _Yp>
1472 inline _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
1473 operator<<(basic_ostream<_CharT, _Traits>& __os, shared_ptr<_Yp> const& __p);
1474
1475 #if _LIBCPP_HAS_THREADS
1476
1477 class _LIBCPP_EXPORTED_FROM_ABI __sp_mut {
1478   void* __lx_;
1479
1480 public:
1481   void lock() _NOEXCEPT;
1482   void unlock() _NOEXCEPT;
1483
1484 private:
1485   _LIBCPP_CONSTEXPR __sp_mut(void*) _NOEXCEPT;
1486   __sp_mut(const __sp_mut&);
1487   __sp_mut& operator=(const __sp_mut&);
1488
1489   friend _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
1490 };
1491
1492 _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
1493
1494 template <class _Tp>
1495 inline _LIBCPP_HIDE_FROM_ABI bool atomic_is_lock_free(const shared_ptr<_Tp>*) {
1496   return false;
1497 }
1498
1499 template <class _Tp>
1500 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load(const shared_ptr<_Tp>* __p) {
1501   __sp_mut& __m = std::__get_sp_mut(__p);
1502   __m.lock();
1503   shared_ptr<_Tp> __q = *__p;
1504   __m.unlock();
1505   return __q;
1506 }
1507
1508 template <class _Tp>
1509 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order) {
1510   return std::atomic_load(__p);
1511 }
1512
1513 template <class _Tp>
1514 _LIBCPP_HIDE_FROM_ABI void atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
1515   __sp_mut& __m = std::__get_sp_mut(__p);
1516   __m.lock();
1517   __p->swap(__r);
1518   __m.unlock();
1519 }
1520
1521 template <class _Tp>
1522 inline _LIBCPP_HIDE_FROM_ABI void atomic_store_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
1523   std::atomic_store(__p, __r);
1524 }
1525
1526 template <class _Tp>
1527 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
1528   __sp_mut& __m = std::__get_sp_mut(__p);
1529   __m.lock();
1530   __p->swap(__r);
1531   __m.unlock();
1532   return __r;
1533 }
1534
1535 template <class _Tp>
1536 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
1537 atomic_exchange_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
1538   return std::atomic_exchange(__p, __r);
1539 }
1540
1541 template <class _Tp>
1542 _LIBCPP_HIDE_FROM_ABI bool
1543 atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
1544   shared_ptr<_Tp> __temp;
1545   __sp_mut& __m = std::__get_sp_mut(__p);
1546   __m.lock();
1547   if (__p->__owner_equivalent(*__v)) {
1548     std::swap(__temp, *__p);
1549     *__p = __w;
1550     __m.unlock();
1551     return true;
1552   }
1553   std::swap(__temp, *__v);
1554   *__v = *__p;
1555   __m.unlock();
1556   return false;
1557 }
1558
1559 template <class _Tp>
1560 inline _LIBCPP_HIDE_FROM_ABI bool
1561 atomic_compare_exchange_weak(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
1562   return std::atomic_compare_exchange_strong(__p, __v, __w);
1563 }
1564
1565 template <class _Tp>
1566 inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_strong_explicit(
1567     shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
1568   return std::atomic_compare_exchange_strong(__p, __v, __w);
1569 }
1570
1571 template <class _Tp>
1572 inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_weak_explicit(
1573     shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
1574   return std::atomic_compare_exchange_weak(__p, __v, __w);
1575 }
1576
1577 #endif // _LIBCPP_HAS_THREADS
1578
1579 _LIBCPP_END_NAMESPACE_STD
1580
1581 _LIBCPP_POP_MACROS
1582
1583 #endif // _LIBCPP___MEMORY_SHARED_PTR_H