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 <__availability>
  14 #include <__compare/compare_three_way.h>
  15 #include <__compare/ordering.h>
  16 #include <__config>
  17 #include <__exception/exception.h>
  18 #include <__functional/binary_function.h>
  19 #include <__functional/operations.h>
  20 #include <__functional/reference_wrapper.h>
  21 #include <__fwd/ostream.h>
  22 #include <__iterator/access.h>
  23 #include <__memory/addressof.h>
  24 #include <__memory/allocation_guard.h>
  25 #include <__memory/allocator.h>
  26 #include <__memory/allocator_destructor.h>
  27 #include <__memory/allocator_traits.h>
  28 #include <__memory/auto_ptr.h>
  29 #include <__memory/compressed_pair.h>
  30 #include <__memory/construct_at.h>
  31 #include <__memory/pointer_traits.h>
  32 #include <__memory/uninitialized_algorithms.h>
  33 #include <__memory/unique_ptr.h>
  34 #include <__type_traits/add_lvalue_reference.h>
  35 #include <__type_traits/conditional.h>
  36 #include <__type_traits/conjunction.h>
  37 #include <__type_traits/disjunction.h>
  38 #include <__type_traits/is_array.h>
  39 #include <__type_traits/is_bounded_array.h>
  40 #include <__type_traits/is_convertible.h>
  41 #include <__type_traits/is_move_constructible.h>
  42 #include <__type_traits/is_reference.h>
  43 #include <__type_traits/is_unbounded_array.h>
  44 #include <__type_traits/nat.h>
  45 #include <__type_traits/negation.h>
  46 #include <__type_traits/remove_extent.h>
  47 #include <__type_traits/remove_reference.h>
  48 #include <__utility/declval.h>
  49 #include <__utility/forward.h>
  50 #include <__utility/move.h>
  51 #include <__utility/swap.h>
  52 #include <__verbose_abort>
  53 #include <cstddef>
  54 #include <new>
  55 #include <typeinfo>
  56 #if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
  57 #  include <__atomic/memory_order.h>
  58 #endif
  59
  60 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  61 #  pragma GCC system_header
  62 #endif
  63
  64 _LIBCPP_BEGIN_NAMESPACE_STD
  65
  66 // NOTE: Relaxed and acq/rel atomics (for increment and decrement respectively)
  67 // should be sufficient for thread safety.
  68 // See https://llvm.org/PR22803
  69 #if defined(__clang__) && __has_builtin(__atomic_add_fetch)          \
  70                        && defined(__ATOMIC_RELAXED)                  \
  71                        && defined(__ATOMIC_ACQ_REL)
  72 #   define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT
  73 #elif defined(_LIBCPP_COMPILER_GCC)
  74 #   define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT
  75 #endif
  76
  77 template <class _ValueType>
  78 inline _LIBCPP_INLINE_VISIBILITY
  79 _ValueType __libcpp_relaxed_load(_ValueType const* __value) {
  80 #if !defined(_LIBCPP_HAS_NO_THREADS) && \
  81     defined(__ATOMIC_RELAXED) &&        \
  82     (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
  83     return __atomic_load_n(__value, __ATOMIC_RELAXED);
  84 #else
  85     return *__value;
  86 #endif
  87 }
  88
  89 template <class _ValueType>
  90 inline _LIBCPP_INLINE_VISIBILITY
  91 _ValueType __libcpp_acquire_load(_ValueType const* __value) {
  92 #if !defined(_LIBCPP_HAS_NO_THREADS) && \
  93     defined(__ATOMIC_ACQUIRE) &&        \
  94     (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
  95     return __atomic_load_n(__value, __ATOMIC_ACQUIRE);
  96 #else
  97     return *__value;
  98 #endif
  99 }
 100
 101 template <class _Tp>
 102 inline _LIBCPP_INLINE_VISIBILITY _Tp
 103 __libcpp_atomic_refcount_increment(_Tp& __t) _NOEXCEPT
 104 {
 105 #if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && !defined(_LIBCPP_HAS_NO_THREADS)
 106     return __atomic_add_fetch(&__t, 1, __ATOMIC_RELAXED);
 107 #else
 108     return __t += 1;
 109 #endif
 110 }
 111
 112 template <class _Tp>
 113 inline _LIBCPP_INLINE_VISIBILITY _Tp
 114 __libcpp_atomic_refcount_decrement(_Tp& __t) _NOEXCEPT
 115 {
 116 #if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && !defined(_LIBCPP_HAS_NO_THREADS)
 117     return __atomic_add_fetch(&__t, -1, __ATOMIC_ACQ_REL);
 118 #else
 119     return __t -= 1;
 120 #endif
 121 }
 122
 123 class _LIBCPP_EXPORTED_FROM_ABI bad_weak_ptr
 124     : public std::exception
 125 {
 126 public:
 127     _LIBCPP_HIDE_FROM_ABI bad_weak_ptr() _NOEXCEPT = default;
 128     _LIBCPP_HIDE_FROM_ABI bad_weak_ptr(const bad_weak_ptr&) _NOEXCEPT = default;
 129     _LIBCPP_HIDE_FROM_ABI bad_weak_ptr& operator=(const bad_weak_ptr&) _NOEXCEPT = default;
 130     ~bad_weak_ptr() _NOEXCEPT override;
 131     const char* what() const  _NOEXCEPT override;
 132 };
 133
 134 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 135 void __throw_bad_weak_ptr()
 136 {
 137 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 138     throw bad_weak_ptr();
 139 #else
 140     _LIBCPP_VERBOSE_ABORT("bad_weak_ptr was thrown in -fno-exceptions mode");
 141 #endif
 142 }
 143
 144 template<class _Tp> class _LIBCPP_TEMPLATE_VIS weak_ptr;
 145
 146 class _LIBCPP_EXPORTED_FROM_ABI __shared_count
 147 {
 148     __shared_count(const __shared_count&);
 149     __shared_count& operator=(const __shared_count&);
 150
 151 protected:
 152     long __shared_owners_;
 153     virtual ~__shared_count();
 154 private:
 155     virtual void __on_zero_shared() _NOEXCEPT = 0;
 156
 157 public:
 158     _LIBCPP_INLINE_VISIBILITY
 159     explicit __shared_count(long __refs = 0) _NOEXCEPT
 160         : __shared_owners_(__refs) {}
 161
 162 #if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
 163     void __add_shared() noexcept;
 164     bool __release_shared() noexcept;
 165 #else
 166     _LIBCPP_INLINE_VISIBILITY
 167     void __add_shared() _NOEXCEPT {
 168       __libcpp_atomic_refcount_increment(__shared_owners_);
 169     }
 170     _LIBCPP_INLINE_VISIBILITY
 171     bool __release_shared() _NOEXCEPT {
 172       if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {
 173         __on_zero_shared();
 174         return true;
 175       }
 176       return false;
 177     }
 178 #endif
 179     _LIBCPP_INLINE_VISIBILITY
 180     long use_count() const _NOEXCEPT {
 181         return __libcpp_relaxed_load(&__shared_owners_) + 1;
 182     }
 183 };
 184
 185 class _LIBCPP_EXPORTED_FROM_ABI __shared_weak_count
 186     : private __shared_count
 187 {
 188     long __shared_weak_owners_;
 189
 190 public:
 191     _LIBCPP_INLINE_VISIBILITY
 192     explicit __shared_weak_count(long __refs = 0) _NOEXCEPT
 193         : __shared_count(__refs),
 194           __shared_weak_owners_(__refs) {}
 195 protected:
 196     ~__shared_weak_count() override;
 197
 198 public:
 199 #if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
 200     void __add_shared() noexcept;
 201     void __add_weak() noexcept;
 202     void __release_shared() noexcept;
 203 #else
 204     _LIBCPP_INLINE_VISIBILITY
 205     void __add_shared() _NOEXCEPT {
 206       __shared_count::__add_shared();
 207     }
 208     _LIBCPP_INLINE_VISIBILITY
 209     void __add_weak() _NOEXCEPT {
 210       __libcpp_atomic_refcount_increment(__shared_weak_owners_);
 211     }
 212     _LIBCPP_INLINE_VISIBILITY
 213     void __release_shared() _NOEXCEPT {
 214       if (__shared_count::__release_shared())
 215         __release_weak();
 216     }
 217 #endif
 218     void __release_weak() _NOEXCEPT;
 219     _LIBCPP_INLINE_VISIBILITY
 220     long use_count() const _NOEXCEPT {return __shared_count::use_count();}
 221     __shared_weak_count* lock() _NOEXCEPT;
 222
 223     virtual const void* __get_deleter(const type_info&) const _NOEXCEPT;
 224 private:
 225     virtual void __on_zero_shared_weak() _NOEXCEPT = 0;
 226 };
 227
 228 template <class _Tp, class _Dp, class _Alloc>
 229 class __shared_ptr_pointer
 230     : public __shared_weak_count
 231 {
 232     __compressed_pair<__compressed_pair<_Tp, _Dp>, _Alloc> __data_;
 233 public:
 234     _LIBCPP_INLINE_VISIBILITY
 235     __shared_ptr_pointer(_Tp __p, _Dp __d, _Alloc __a)
 236         :  __data_(__compressed_pair<_Tp, _Dp>(__p, _VSTD::move(__d)), _VSTD::move(__a)) {}
 237
 238 #ifndef _LIBCPP_HAS_NO_RTTI
 239     _LIBCPP_HIDE_FROM_ABI_VIRTUAL const void* __get_deleter(const type_info&) const _NOEXCEPT override;
 240 #endif
 241
 242 private:
 243     _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override;
 244     _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override;
 245 };
 246
 247 #ifndef _LIBCPP_HAS_NO_RTTI
 248
 249 template <class _Tp, class _Dp, class _Alloc>
 250 const void*
 251 __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__get_deleter(const type_info& __t) const _NOEXCEPT
 252 {
 253     return __t == typeid(_Dp) ? _VSTD::addressof(__data_.first().second()) : nullptr;
 254 }
 255
 256 #endif // _LIBCPP_HAS_NO_RTTI
 257
 258 template <class _Tp, class _Dp, class _Alloc>
 259 void
 260 __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared() _NOEXCEPT
 261 {
 262     __data_.first().second()(__data_.first().first());
 263     __data_.first().second().~_Dp();
 264 }
 265
 266 template <class _Tp, class _Dp, class _Alloc>
 267 void
 268 __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared_weak() _NOEXCEPT
 269 {
 270     typedef typename __allocator_traits_rebind<_Alloc, __shared_ptr_pointer>::type _Al;
 271     typedef allocator_traits<_Al> _ATraits;
 272     typedef pointer_traits<typename _ATraits::pointer> _PTraits;
 273
 274     _Al __a(__data_.second());
 275     __data_.second().~_Alloc();
 276     __a.deallocate(_PTraits::pointer_to(*this), 1);
 277 }
 278
 279 // This tag is used to instantiate an allocator type. The various shared_ptr control blocks
 280 // detect that the allocator has been instantiated for this type and perform alternative
 281 // initialization/destruction based on that.
 282 struct __for_overwrite_tag {};
 283
 284 template <class _Tp, class _Alloc>
 285 struct __shared_ptr_emplace
 286     : __shared_weak_count
 287 {
 288     template <class... _Args, class _Allocator = _Alloc, __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 289     _LIBCPP_HIDE_FROM_ABI
 290     explicit __shared_ptr_emplace(_Alloc __a, _Args&& ...)
 291         : __storage_(_VSTD::move(__a))
 292     {
 293         static_assert(sizeof...(_Args) == 0, "No argument should be provided to the control block when using _for_overwrite");
 294         ::new ((void*)__get_elem()) _Tp;
 295     }
 296
 297     template <class... _Args, class _Allocator = _Alloc, __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 298     _LIBCPP_HIDE_FROM_ABI
 299     explicit __shared_ptr_emplace(_Alloc __a, _Args&& ...__args)
 300         : __storage_(_VSTD::move(__a))
 301     {
 302         using _TpAlloc = typename __allocator_traits_rebind<_Alloc, _Tp>::type;
 303         _TpAlloc __tmp(*__get_alloc());
 304         allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), _VSTD::forward<_Args>(__args)...);
 305     }
 306
 307     _LIBCPP_HIDE_FROM_ABI
 308     _Alloc* __get_alloc() _NOEXCEPT { return __storage_.__get_alloc(); }
 309
 310     _LIBCPP_HIDE_FROM_ABI
 311     _Tp* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }
 312
 313 private:
 314     template <class _Allocator = _Alloc, __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 315     _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
 316         __get_elem()->~_Tp();
 317     }
 318
 319     template <class _Allocator = _Alloc, __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 320     _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
 321         using _TpAlloc = typename __allocator_traits_rebind<_Allocator, _Tp>::type;
 322         _TpAlloc __tmp(*__get_alloc());
 323         allocator_traits<_TpAlloc>::destroy(__tmp, __get_elem());
 324     }
 325
 326     _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
 327         __on_zero_shared_impl();
 328     }
 329
 330     _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
 331         using _ControlBlockAlloc = typename __allocator_traits_rebind<_Alloc, __shared_ptr_emplace>::type;
 332         using _ControlBlockPointer = typename allocator_traits<_ControlBlockAlloc>::pointer;
 333         _ControlBlockAlloc __tmp(*__get_alloc());
 334         __storage_.~_Storage();
 335         allocator_traits<_ControlBlockAlloc>::deallocate(__tmp,
 336             pointer_traits<_ControlBlockPointer>::pointer_to(*this), 1);
 337     }
 338
 339     // This class implements the control block for non-array shared pointers created
 340     // through `std::allocate_shared` and `std::make_shared`.
 341     //
 342     // In previous versions of the library, we used a compressed pair to store
 343     // both the _Alloc and the _Tp. This implies using EBO, which is incompatible
 344     // with Allocator construction for _Tp. To allow implementing P0674 in C++20,
 345     // we now use a properly aligned char buffer while making sure that we maintain
 346     // the same layout that we had when we used a compressed pair.
 347     using _CompressedPair = __compressed_pair<_Alloc, _Tp>;
 348     struct _ALIGNAS_TYPE(_CompressedPair) _Storage {
 349         char __blob_[sizeof(_CompressedPair)];
 350
 351         _LIBCPP_HIDE_FROM_ABI explicit _Storage(_Alloc&& __a) {
 352             ::new ((void*)__get_alloc()) _Alloc(_VSTD::move(__a));
 353         }
 354         _LIBCPP_HIDE_FROM_ABI ~_Storage() {
 355             __get_alloc()->~_Alloc();
 356         }
 357         _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT {
 358             _CompressedPair *__as_pair = reinterpret_cast<_CompressedPair*>(__blob_);
 359             typename _CompressedPair::_Base1* __first = _CompressedPair::__get_first_base(__as_pair);
 360             _Alloc *__alloc = reinterpret_cast<_Alloc*>(__first);
 361             return __alloc;
 362         }
 363         _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _Tp* __get_elem() _NOEXCEPT {
 364             _CompressedPair *__as_pair = reinterpret_cast<_CompressedPair*>(__blob_);
 365             typename _CompressedPair::_Base2* __second = _CompressedPair::__get_second_base(__as_pair);
 366             _Tp *__elem = reinterpret_cast<_Tp*>(__second);
 367             return __elem;
 368         }
 369     };
 370
 371     static_assert(_LIBCPP_ALIGNOF(_Storage) == _LIBCPP_ALIGNOF(_CompressedPair), "");
 372     static_assert(sizeof(_Storage) == sizeof(_CompressedPair), "");
 373     _Storage __storage_;
 374 };
 375
 376 struct __shared_ptr_dummy_rebind_allocator_type;
 377 template <>
 378 class _LIBCPP_TEMPLATE_VIS allocator<__shared_ptr_dummy_rebind_allocator_type>
 379 {
 380 public:
 381     template <class _Other>
 382     struct rebind
 383     {
 384         typedef allocator<_Other> other;
 385     };
 386 };
 387
 388 template<class _Tp> class _LIBCPP_TEMPLATE_VIS enable_shared_from_this;
 389
 390 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.general-6
 391 // A pointer type Y* is said to be compatible with a pointer type T*
 392 // when either Y* is convertible to T* or Y is U[N] and T is cv U[].
 393 #if _LIBCPP_STD_VER >= 17
 394 template <class _Yp, class _Tp>
 395 struct __bounded_convertible_to_unbounded : false_type {};
 396
 397 template <class _Up, std::size_t _Np, class _Tp>
 398 struct __bounded_convertible_to_unbounded<_Up[_Np], _Tp>
 399         : is_same<__remove_cv_t<_Tp>, _Up[]> {};
 400
 401 template <class _Yp, class _Tp>
 402 struct __compatible_with
 403     : _Or<
 404         is_convertible<_Yp*, _Tp*>,
 405         __bounded_convertible_to_unbounded<_Yp, _Tp>
 406     > {};
 407 #else
 408 template <class _Yp, class _Tp>
 409 struct __compatible_with
 410     : is_convertible<_Yp*, _Tp*> {};
 411 #endif // _LIBCPP_STD_VER >= 17
 412
 413 // Constructors that take raw pointers have a different set of "compatible" constraints
 414 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.const-9.1
 415 // - If T is an array type, then either T is U[N] and Y(*)[N] is convertible to T*,
 416 //   or T is U[] and Y(*)[] is convertible to T*.
 417 // - If T is not an array type, then Y* is convertible to T*.
 418 #if _LIBCPP_STD_VER >= 17
 419 template <class _Yp, class _Tp, class = void>
 420 struct __raw_pointer_compatible_with : _And<
 421         _Not<is_array<_Tp>>,
 422         is_convertible<_Yp*, _Tp*>
 423         > {};
 424
 425 template <class _Yp, class _Up, std::size_t _Np>
 426 struct __raw_pointer_compatible_with<_Yp, _Up[_Np], __enable_if_t<
 427             is_convertible<_Yp(*)[_Np], _Up(*)[_Np]>::value> >
 428         : true_type {};
 429
 430 template <class _Yp, class _Up>
 431 struct __raw_pointer_compatible_with<_Yp, _Up[], __enable_if_t<
 432             is_convertible<_Yp(*)[], _Up(*)[]>::value> >
 433         : true_type {};
 434
 435 #else
 436 template <class _Yp, class _Tp>
 437 struct __raw_pointer_compatible_with
 438     : is_convertible<_Yp*, _Tp*> {};
 439 #endif // _LIBCPP_STD_VER >= 17
 440
 441
 442 template <class _Ptr, class = void>
 443 struct __is_deletable : false_type { };
 444 template <class _Ptr>
 445 struct __is_deletable<_Ptr, decltype(delete std::declval<_Ptr>())> : true_type { };
 446
 447 template <class _Ptr, class = void>
 448 struct __is_array_deletable : false_type { };
 449 template <class _Ptr>
 450 struct __is_array_deletable<_Ptr, decltype(delete[] std::declval<_Ptr>())> : true_type { };
 451
 452 template <class _Dp, class _Pt,
 453     class = decltype(std::declval<_Dp>()(std::declval<_Pt>()))>
 454 true_type __well_formed_deleter_test(int);
 455
 456 template <class, class>
 457 false_type __well_formed_deleter_test(...);
 458
 459 template <class _Dp, class _Pt>
 460 struct __well_formed_deleter : decltype(std::__well_formed_deleter_test<_Dp, _Pt>(0)) {};
 461
 462 template<class _Dp, class _Yp, class _Tp>
 463 struct __shared_ptr_deleter_ctor_reqs
 464 {
 465     static const bool value = __raw_pointer_compatible_with<_Yp, _Tp>::value &&
 466                               is_move_constructible<_Dp>::value &&
 467                               __well_formed_deleter<_Dp, _Yp*>::value;
 468 };
 469
 470 #if defined(_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI)
 471 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI __attribute__((__trivial_abi__))
 472 #else
 473 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI
 474 #endif
 475
 476 template<class _Tp>
 477 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS shared_ptr
 478 {
 479 public:
 480 #if _LIBCPP_STD_VER >= 17
 481     typedef weak_ptr<_Tp> weak_type;
 482     typedef remove_extent_t<_Tp> element_type;
 483 #else
 484     typedef _Tp element_type;
 485 #endif
 486
 487 private:
 488     element_type*      __ptr_;
 489     __shared_weak_count* __cntrl_;
 490
 491 public:
 492     _LIBCPP_HIDE_FROM_ABI
 493     _LIBCPP_CONSTEXPR shared_ptr() _NOEXCEPT
 494         : __ptr_(nullptr),
 495           __cntrl_(nullptr)
 496     { }
 497
 498     _LIBCPP_HIDE_FROM_ABI
 499     _LIBCPP_CONSTEXPR shared_ptr(nullptr_t) _NOEXCEPT
 500         : __ptr_(nullptr),
 501           __cntrl_(nullptr)
 502     { }
 503
 504     template<class _Yp, class = __enable_if_t<
 505         _And<
 506             __raw_pointer_compatible_with<_Yp, _Tp>
 507             // In C++03 we get errors when trying to do SFINAE with the
 508             // delete operator, so we always pretend that it's deletable.
 509             // The same happens on GCC.
 510 #if !defined(_LIBCPP_CXX03_LANG) && !defined(_LIBCPP_COMPILER_GCC)
 511             , _If<is_array<_Tp>::value, __is_array_deletable<_Yp*>, __is_deletable<_Yp*> >
 512 #endif
 513         >::value
 514     > >
 515     _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(_Yp* __p) : __ptr_(__p) {
 516         unique_ptr<_Yp> __hold(__p);
 517         typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 518         typedef __shared_ptr_pointer<_Yp*, __shared_ptr_default_delete<_Tp, _Yp>, _AllocT> _CntrlBlk;
 519         __cntrl_ = new _CntrlBlk(__p, __shared_ptr_default_delete<_Tp, _Yp>(), _AllocT());
 520         __hold.release();
 521         __enable_weak_this(__p, __p);
 522     }
 523
 524     template<class _Yp, class _Dp, class = __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value> >
 525     _LIBCPP_HIDE_FROM_ABI
 526     shared_ptr(_Yp* __p, _Dp __d)
 527         : __ptr_(__p)
 528     {
 529 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 530         try
 531         {
 532 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 533             typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 534             typedef __shared_ptr_pointer<_Yp*, _Dp, _AllocT> _CntrlBlk;
 535 #ifndef _LIBCPP_CXX03_LANG
 536             __cntrl_ = new _CntrlBlk(__p, _VSTD::move(__d), _AllocT());
 537 #else
 538             __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
 539 #endif // not _LIBCPP_CXX03_LANG
 540             __enable_weak_this(__p, __p);
 541 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 542         }
 543         catch (...)
 544         {
 545             __d(__p);
 546             throw;
 547         }
 548 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 549     }
 550
 551     template<class _Yp, class _Dp, class _Alloc, class = __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value> >
 552     _LIBCPP_HIDE_FROM_ABI
 553     shared_ptr(_Yp* __p, _Dp __d, _Alloc __a)
 554         : __ptr_(__p)
 555     {
 556 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 557         try
 558         {
 559 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 560             typedef __shared_ptr_pointer<_Yp*, _Dp, _Alloc> _CntrlBlk;
 561             typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
 562             typedef __allocator_destructor<_A2> _D2;
 563             _A2 __a2(__a);
 564             unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
 565             ::new ((void*)_VSTD::addressof(*__hold2.get()))
 566 #ifndef _LIBCPP_CXX03_LANG
 567                 _CntrlBlk(__p, _VSTD::move(__d), __a);
 568 #else
 569                 _CntrlBlk(__p, __d, __a);
 570 #endif // not _LIBCPP_CXX03_LANG
 571             __cntrl_ = _VSTD::addressof(*__hold2.release());
 572             __enable_weak_this(__p, __p);
 573 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 574         }
 575         catch (...)
 576         {
 577             __d(__p);
 578             throw;
 579         }
 580 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 581     }
 582
 583     template<class _Dp>
 584     _LIBCPP_HIDE_FROM_ABI
 585     shared_ptr(nullptr_t __p, _Dp __d)
 586         : __ptr_(nullptr)
 587     {
 588 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 589         try
 590         {
 591 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 592             typedef typename __shared_ptr_default_allocator<_Tp>::type _AllocT;
 593             typedef __shared_ptr_pointer<nullptr_t, _Dp, _AllocT> _CntrlBlk;
 594 #ifndef _LIBCPP_CXX03_LANG
 595             __cntrl_ = new _CntrlBlk(__p, _VSTD::move(__d), _AllocT());
 596 #else
 597             __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
 598 #endif // not _LIBCPP_CXX03_LANG
 599 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 600         }
 601         catch (...)
 602         {
 603             __d(__p);
 604             throw;
 605         }
 606 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 607     }
 608
 609     template<class _Dp, class _Alloc>
 610     _LIBCPP_HIDE_FROM_ABI
 611     shared_ptr(nullptr_t __p, _Dp __d, _Alloc __a)
 612         : __ptr_(nullptr)
 613     {
 614 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 615         try
 616         {
 617 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 618             typedef __shared_ptr_pointer<nullptr_t, _Dp, _Alloc> _CntrlBlk;
 619             typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
 620             typedef __allocator_destructor<_A2> _D2;
 621             _A2 __a2(__a);
 622             unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
 623             ::new ((void*)_VSTD::addressof(*__hold2.get()))
 624 #ifndef _LIBCPP_CXX03_LANG
 625                 _CntrlBlk(__p, _VSTD::move(__d), __a);
 626 #else
 627                 _CntrlBlk(__p, __d, __a);
 628 #endif // not _LIBCPP_CXX03_LANG
 629             __cntrl_ = _VSTD::addressof(*__hold2.release());
 630 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 631         }
 632         catch (...)
 633         {
 634             __d(__p);
 635             throw;
 636         }
 637 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 638     }
 639
 640     template<class _Yp>
 641     _LIBCPP_HIDE_FROM_ABI
 642     shared_ptr(const shared_ptr<_Yp>& __r, element_type *__p) _NOEXCEPT
 643         : __ptr_(__p),
 644           __cntrl_(__r.__cntrl_)
 645     {
 646         if (__cntrl_)
 647             __cntrl_->__add_shared();
 648     }
 649
 650 // LWG-2996
 651 // We don't backport because it is an evolutionary change.
 652 #if _LIBCPP_STD_VER >= 20
 653     template <class _Yp>
 654     _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
 655         : __ptr_(__p),
 656           __cntrl_(__r.__cntrl_) {
 657       __r.__ptr_   = nullptr;
 658       __r.__cntrl_ = nullptr;
 659     }
 660 #endif
 661
 662     _LIBCPP_HIDE_FROM_ABI
 663     shared_ptr(const shared_ptr& __r) _NOEXCEPT
 664         : __ptr_(__r.__ptr_),
 665           __cntrl_(__r.__cntrl_)
 666     {
 667         if (__cntrl_)
 668             __cntrl_->__add_shared();
 669     }
 670
 671     template<class _Yp, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
 672     _LIBCPP_HIDE_FROM_ABI
 673     shared_ptr(const shared_ptr<_Yp>& __r) _NOEXCEPT
 674         : __ptr_(__r.__ptr_),
 675           __cntrl_(__r.__cntrl_)
 676     {
 677         if (__cntrl_)
 678             __cntrl_->__add_shared();
 679     }
 680
 681     _LIBCPP_HIDE_FROM_ABI
 682     shared_ptr(shared_ptr&& __r) _NOEXCEPT
 683         : __ptr_(__r.__ptr_),
 684           __cntrl_(__r.__cntrl_)
 685     {
 686         __r.__ptr_ = nullptr;
 687         __r.__cntrl_ = nullptr;
 688     }
 689
 690     template<class _Yp, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
 691     _LIBCPP_HIDE_FROM_ABI
 692     shared_ptr(shared_ptr<_Yp>&& __r) _NOEXCEPT
 693         : __ptr_(__r.__ptr_),
 694           __cntrl_(__r.__cntrl_)
 695     {
 696         __r.__ptr_ = nullptr;
 697         __r.__cntrl_ = nullptr;
 698     }
 699
 700     template<class _Yp, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
 701     _LIBCPP_HIDE_FROM_ABI
 702     explicit shared_ptr(const weak_ptr<_Yp>& __r)
 703         : __ptr_(__r.__ptr_),
 704           __cntrl_(__r.__cntrl_ ? __r.__cntrl_->lock() : __r.__cntrl_)
 705     {
 706         if (__cntrl_ == nullptr)
 707             __throw_bad_weak_ptr();
 708     }
 709
 710 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
 711     template<class _Yp, class = __enable_if_t<is_convertible<_Yp*, element_type*>::value> >
 712     _LIBCPP_HIDE_FROM_ABI
 713     shared_ptr(auto_ptr<_Yp>&& __r)
 714         : __ptr_(__r.get())
 715     {
 716         typedef __shared_ptr_pointer<_Yp*, default_delete<_Yp>, allocator<_Yp> > _CntrlBlk;
 717         __cntrl_ = new _CntrlBlk(__r.get(), default_delete<_Yp>(), allocator<_Yp>());
 718         __enable_weak_this(__r.get(), __r.get());
 719         __r.release();
 720     }
 721 #endif
 722
 723     template <class _Yp, class _Dp, class = __enable_if_t<
 724         !is_lvalue_reference<_Dp>::value &&
 725          __compatible_with<_Yp, _Tp>::value &&
 726          is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value
 727     > >
 728     _LIBCPP_HIDE_FROM_ABI
 729     shared_ptr(unique_ptr<_Yp, _Dp>&& __r)
 730         : __ptr_(__r.get())
 731     {
 732 #if _LIBCPP_STD_VER >= 14
 733         if (__ptr_ == nullptr)
 734             __cntrl_ = nullptr;
 735         else
 736 #endif
 737         {
 738             typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 739             typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer, _Dp, _AllocT> _CntrlBlk;
 740             __cntrl_ = new _CntrlBlk(__r.get(), std::move(__r.get_deleter()), _AllocT());
 741             __enable_weak_this(__r.get(), __r.get());
 742         }
 743         __r.release();
 744     }
 745
 746     template <class _Yp, class _Dp, class = void, class = __enable_if_t<
 747         is_lvalue_reference<_Dp>::value &&
 748          __compatible_with<_Yp, _Tp>::value &&
 749         is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value
 750     > >
 751     _LIBCPP_HIDE_FROM_ABI
 752     shared_ptr(unique_ptr<_Yp, _Dp>&& __r)
 753         : __ptr_(__r.get())
 754     {
 755 #if _LIBCPP_STD_VER >= 14
 756         if (__ptr_ == nullptr)
 757             __cntrl_ = nullptr;
 758         else
 759 #endif
 760         {
 761             typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 762             typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer,
 763                                         reference_wrapper<__libcpp_remove_reference_t<_Dp> >,
 764                                         _AllocT> _CntrlBlk;
 765             __cntrl_ = new _CntrlBlk(__r.get(), _VSTD::ref(__r.get_deleter()), _AllocT());
 766             __enable_weak_this(__r.get(), __r.get());
 767         }
 768         __r.release();
 769     }
 770
 771     _LIBCPP_HIDE_FROM_ABI
 772     ~shared_ptr()
 773     {
 774         if (__cntrl_)
 775             __cntrl_->__release_shared();
 776     }
 777
 778     _LIBCPP_HIDE_FROM_ABI
 779     shared_ptr<_Tp>& operator=(const shared_ptr& __r) _NOEXCEPT
 780     {
 781         shared_ptr(__r).swap(*this);
 782         return *this;
 783     }
 784
 785     template<class _Yp, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
 786     _LIBCPP_HIDE_FROM_ABI
 787     shared_ptr<_Tp>& operator=(const shared_ptr<_Yp>& __r) _NOEXCEPT
 788     {
 789         shared_ptr(__r).swap(*this);
 790         return *this;
 791     }
 792
 793     _LIBCPP_HIDE_FROM_ABI
 794     shared_ptr<_Tp>& operator=(shared_ptr&& __r) _NOEXCEPT
 795     {
 796         shared_ptr(_VSTD::move(__r)).swap(*this);
 797         return *this;
 798     }
 799
 800     template<class _Yp, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
 801     _LIBCPP_HIDE_FROM_ABI
 802     shared_ptr<_Tp>& operator=(shared_ptr<_Yp>&& __r)
 803     {
 804         shared_ptr(_VSTD::move(__r)).swap(*this);
 805         return *this;
 806     }
 807
 808 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
 809     template<class _Yp, class = __enable_if_t<
 810         !is_array<_Yp>::value &&
 811         is_convertible<_Yp*, typename shared_ptr<_Tp>::element_type*>::value
 812     > >
 813     _LIBCPP_HIDE_FROM_ABI
 814     shared_ptr<_Tp>& operator=(auto_ptr<_Yp>&& __r)
 815     {
 816         shared_ptr(_VSTD::move(__r)).swap(*this);
 817         return *this;
 818     }
 819 #endif
 820
 821     template <class _Yp, class _Dp, class = __enable_if_t<_And<
 822         __compatible_with<_Yp, _Tp>,
 823         is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>
 824     >::value> >
 825     _LIBCPP_HIDE_FROM_ABI
 826     shared_ptr<_Tp>& operator=(unique_ptr<_Yp, _Dp>&& __r)
 827     {
 828         shared_ptr(_VSTD::move(__r)).swap(*this);
 829         return *this;
 830     }
 831
 832     _LIBCPP_HIDE_FROM_ABI
 833     void swap(shared_ptr& __r) _NOEXCEPT
 834     {
 835         _VSTD::swap(__ptr_, __r.__ptr_);
 836         _VSTD::swap(__cntrl_, __r.__cntrl_);
 837     }
 838
 839     _LIBCPP_HIDE_FROM_ABI
 840     void reset() _NOEXCEPT
 841     {
 842         shared_ptr().swap(*this);
 843     }
 844
 845     template<class _Yp, class = __enable_if_t<
 846         __raw_pointer_compatible_with<_Yp, _Tp>::value
 847     > >
 848     _LIBCPP_HIDE_FROM_ABI
 849     void reset(_Yp* __p)
 850     {
 851         shared_ptr(__p).swap(*this);
 852     }
 853
 854     template<class _Yp, class _Dp, class = __enable_if_t<
 855         __shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value> >
 856     _LIBCPP_HIDE_FROM_ABI
 857     void reset(_Yp* __p, _Dp __d)
 858     {
 859         shared_ptr(__p, __d).swap(*this);
 860     }
 861
 862     template<class _Yp, class _Dp, class _Alloc, class = __enable_if_t<
 863         __shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value> >
 864     _LIBCPP_HIDE_FROM_ABI
 865     void reset(_Yp* __p, _Dp __d, _Alloc __a)
 866     {
 867         shared_ptr(__p, __d, __a).swap(*this);
 868     }
 869
 870     _LIBCPP_HIDE_FROM_ABI
 871     element_type* get() const _NOEXCEPT
 872     {
 873         return __ptr_;
 874     }
 875
 876     _LIBCPP_HIDE_FROM_ABI
 877     __add_lvalue_reference_t<element_type> operator*() const _NOEXCEPT
 878     {
 879         return *__ptr_;
 880     }
 881
 882     _LIBCPP_HIDE_FROM_ABI
 883     element_type* operator->() const _NOEXCEPT
 884     {
 885         static_assert(!is_array<_Tp>::value,
 886                       "std::shared_ptr<T>::operator-> is only valid when T is not an array type.");
 887         return __ptr_;
 888     }
 889
 890     _LIBCPP_HIDE_FROM_ABI
 891     long use_count() const _NOEXCEPT
 892     {
 893         return __cntrl_ ? __cntrl_->use_count() : 0;
 894     }
 895
 896     _LIBCPP_HIDE_FROM_ABI
 897     bool unique() const _NOEXCEPT
 898     {
 899         return use_count() == 1;
 900     }
 901
 902     _LIBCPP_HIDE_FROM_ABI
 903     explicit operator bool() const _NOEXCEPT
 904     {
 905         return get() != nullptr;
 906     }
 907
 908     template <class _Up>
 909     _LIBCPP_HIDE_FROM_ABI
 910     bool owner_before(shared_ptr<_Up> const& __p) const _NOEXCEPT
 911     {
 912         return __cntrl_ < __p.__cntrl_;
 913     }
 914
 915     template <class _Up>
 916     _LIBCPP_HIDE_FROM_ABI
 917     bool owner_before(weak_ptr<_Up> const& __p) const _NOEXCEPT
 918     {
 919         return __cntrl_ < __p.__cntrl_;
 920     }
 921
 922     _LIBCPP_HIDE_FROM_ABI
 923     bool __owner_equivalent(const shared_ptr& __p) const
 924     {
 925         return __cntrl_ == __p.__cntrl_;
 926     }
 927
 928 #if _LIBCPP_STD_VER >= 17
 929     _LIBCPP_HIDE_FROM_ABI
 930     __add_lvalue_reference_t<element_type> operator[](ptrdiff_t __i) const
 931     {
 932             static_assert(is_array<_Tp>::value,
 933                           "std::shared_ptr<T>::operator[] is only valid when T is an array type.");
 934             return __ptr_[__i];
 935     }
 936 #endif
 937
 938 #ifndef _LIBCPP_HAS_NO_RTTI
 939     template <class _Dp>
 940     _LIBCPP_HIDE_FROM_ABI
 941     _Dp* __get_deleter() const _NOEXCEPT
 942     {
 943         return static_cast<_Dp*>(__cntrl_
 944                     ? const_cast<void *>(__cntrl_->__get_deleter(typeid(_Dp)))
 945                       : nullptr);
 946     }
 947 #endif // _LIBCPP_HAS_NO_RTTI
 948
 949     template<class _Yp, class _CntrlBlk>
 950     _LIBCPP_HIDE_FROM_ABI
 951     static shared_ptr<_Tp> __create_with_control_block(_Yp* __p, _CntrlBlk* __cntrl) _NOEXCEPT
 952     {
 953         shared_ptr<_Tp> __r;
 954         __r.__ptr_ = __p;
 955         __r.__cntrl_ = __cntrl;
 956         __r.__enable_weak_this(__r.__ptr_, __r.__ptr_);
 957         return __r;
 958     }
 959
 960 private:
 961     template <class _Yp, bool = is_function<_Yp>::value>
 962     struct __shared_ptr_default_allocator
 963     {
 964         typedef allocator<_Yp> type;
 965     };
 966
 967     template <class _Yp>
 968     struct __shared_ptr_default_allocator<_Yp, true>
 969     {
 970         typedef allocator<__shared_ptr_dummy_rebind_allocator_type> type;
 971     };
 972
 973     template <class _Yp, class _OrigPtr, class = __enable_if_t<
 974         is_convertible<_OrigPtr*, const enable_shared_from_this<_Yp>*>::value
 975     > >
 976     _LIBCPP_HIDE_FROM_ABI
 977     void __enable_weak_this(const enable_shared_from_this<_Yp>* __e, _OrigPtr* __ptr) _NOEXCEPT
 978     {
 979         typedef __remove_cv_t<_Yp> _RawYp;
 980         if (__e && __e->__weak_this_.expired())
 981         {
 982             __e->__weak_this_ = shared_ptr<_RawYp>(*this,
 983                 const_cast<_RawYp*>(static_cast<const _Yp*>(__ptr)));
 984         }
 985     }
 986
 987     _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(...) _NOEXCEPT { }
 988
 989     template <class, class _Yp>
 990     struct __shared_ptr_default_delete
 991         : default_delete<_Yp>
 992     { };
 993
 994     template <class _Yp, class _Un, size_t _Sz>
 995     struct __shared_ptr_default_delete<_Yp[_Sz], _Un>
 996         : default_delete<_Yp[]>
 997     { };
 998
 999     template <class _Yp, class _Un>
1000     struct __shared_ptr_default_delete<_Yp[], _Un>
1001         : default_delete<_Yp[]>
1002     { };
1003
1004     template <class _Up> friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
1005     template <class _Up> friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
1006 };
1007
1008 #if _LIBCPP_STD_VER >= 17
1009 template<class _Tp>
1010 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
1011 template<class _Tp, class _Dp>
1012 shared_ptr(unique_ptr<_Tp, _Dp>) -> shared_ptr<_Tp>;
1013 #endif
1014
1015 //
1016 // std::allocate_shared and std::make_shared
1017 //
1018 template<class _Tp, class _Alloc, class ..._Args, class = __enable_if_t<!is_array<_Tp>::value> >
1019 _LIBCPP_HIDE_FROM_ABI
1020 shared_ptr<_Tp> allocate_shared(const _Alloc& __a, _Args&& ...__args)
1021 {
1022     using _ControlBlock = __shared_ptr_emplace<_Tp, _Alloc>;
1023     using _ControlBlockAllocator = typename __allocator_traits_rebind<_Alloc, _ControlBlock>::type;
1024     __allocation_guard<_ControlBlockAllocator> __guard(__a, 1);
1025     ::new ((void*)_VSTD::addressof(*__guard.__get())) _ControlBlock(__a, _VSTD::forward<_Args>(__args)...);
1026     auto __control_block = __guard.__release_ptr();
1027     return shared_ptr<_Tp>::__create_with_control_block((*__control_block).__get_elem(), _VSTD::addressof(*__control_block));
1028 }
1029
1030 template<class _Tp, class ..._Args, class = __enable_if_t<!is_array<_Tp>::value> >
1031 _LIBCPP_HIDE_FROM_ABI
1032 shared_ptr<_Tp> make_shared(_Args&& ...__args)
1033 {
1034     return _VSTD::allocate_shared<_Tp>(allocator<_Tp>(), _VSTD::forward<_Args>(__args)...);
1035 }
1036
1037 #if _LIBCPP_STD_VER >= 20
1038
1039 template<class _Tp, class _Alloc, __enable_if_t<!is_array<_Tp>::value, int> = 0>
1040 _LIBCPP_HIDE_FROM_ABI
1041 shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a)
1042 {
1043     using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
1044     _ForOverwriteAllocator __alloc(__a);
1045     return std::allocate_shared<_Tp>(__alloc);
1046 }
1047
1048 template<class _Tp, __enable_if_t<!is_array<_Tp>::value, int> = 0>
1049 _LIBCPP_HIDE_FROM_ABI
1050 shared_ptr<_Tp> make_shared_for_overwrite()
1051 {
1052     return std::allocate_shared_for_overwrite<_Tp>(allocator<_Tp>());
1053 }
1054
1055 #endif // _LIBCPP_STD_VER >= 20
1056
1057 #if _LIBCPP_STD_VER >= 17
1058
1059 template <size_t _Alignment>
1060 struct __sp_aligned_storage {
1061     alignas(_Alignment) char __storage[_Alignment];
1062 };
1063
1064 template <class _Tp, class _Alloc>
1065 struct __unbounded_array_control_block;
1066
1067 template <class _Tp, class _Alloc>
1068 struct __unbounded_array_control_block<_Tp[], _Alloc> : __shared_weak_count
1069 {
1070     _LIBCPP_HIDE_FROM_ABI constexpr
1071     _Tp* __get_data() noexcept { return __data_; }
1072
1073     _LIBCPP_HIDE_FROM_ABI
1074     explicit __unbounded_array_control_block(_Alloc const& __alloc, size_t __count, _Tp const& __arg)
1075         : __alloc_(__alloc), __count_(__count)
1076     {
1077         std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::begin(__data_), __count_, __arg);
1078     }
1079
1080     _LIBCPP_HIDE_FROM_ABI
1081     explicit __unbounded_array_control_block(_Alloc const& __alloc, size_t __count)
1082         : __alloc_(__alloc), __count_(__count)
1083     {
1084 #if _LIBCPP_STD_VER >= 20
1085         if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
1086             // We are purposefully not using an allocator-aware default construction because the spec says so.
1087             // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
1088             std::uninitialized_default_construct_n(std::begin(__data_), __count_);
1089         } else {
1090             std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
1091         }
1092 #else
1093         std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
1094 #endif
1095     }
1096
1097     // Returns the number of bytes required to store a control block followed by the given number
1098     // of elements of _Tp, with the whole storage being aligned to a multiple of _Tp's alignment.
1099     _LIBCPP_HIDE_FROM_ABI
1100     static constexpr size_t __bytes_for(size_t __elements) {
1101         // When there's 0 elements, the control block alone is enough since it holds one element.
1102         // Otherwise, we allocate one fewer element than requested because the control block already
1103         // holds one. Also, we use the bitwise formula below to ensure that we allocate enough bytes
1104         // for the whole allocation to be a multiple of _Tp's alignment. That formula is taken from [1].
1105         //
1106         // [1]: https://en.wikipedia.org/wiki/Data_structure_alignment#Computing_padding
1107         size_t __bytes = __elements == 0 ? sizeof(__unbounded_array_control_block)
1108                                          : (__elements - 1) * sizeof(_Tp) + sizeof(__unbounded_array_control_block);
1109         constexpr size_t __align = alignof(_Tp);
1110         return (__bytes + __align - 1) & ~(__align - 1);
1111     }
1112
1113     _LIBCPP_HIDE_FROM_ABI_VIRTUAL
1114     ~__unbounded_array_control_block() override { } // can't be `= default` because of the sometimes-non-trivial union member __data_
1115
1116 private:
1117     _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
1118 #if _LIBCPP_STD_VER >= 20
1119         if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
1120             std::__reverse_destroy(__data_, __data_ + __count_);
1121         } else {
1122             __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
1123             std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
1124         }
1125 #else
1126         __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
1127         std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
1128 #endif
1129     }
1130
1131     _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
1132         using _AlignedStorage = __sp_aligned_storage<alignof(__unbounded_array_control_block)>;
1133         using _StorageAlloc = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
1134         using _PointerTraits = pointer_traits<typename allocator_traits<_StorageAlloc>::pointer>;
1135
1136         _StorageAlloc __tmp(__alloc_);
1137         __alloc_.~_Alloc();
1138         size_t __size = __unbounded_array_control_block::__bytes_for(__count_);
1139         _AlignedStorage* __storage = reinterpret_cast<_AlignedStorage*>(this);
1140         allocator_traits<_StorageAlloc>::deallocate(
1141             __tmp, _PointerTraits::pointer_to(*__storage), __size / sizeof(_AlignedStorage));
1142     }
1143
1144     _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
1145     size_t __count_;
1146     union {
1147         _Tp __data_[1];
1148     };
1149 };
1150
1151 template<class _Array, class _Alloc, class... _Arg>
1152 _LIBCPP_HIDE_FROM_ABI
1153 shared_ptr<_Array> __allocate_shared_unbounded_array(const _Alloc& __a, size_t __n, _Arg&& ...__arg)
1154 {
1155     static_assert(__libcpp_is_unbounded_array<_Array>::value);
1156     // We compute the number of bytes necessary to hold the control block and the
1157     // array elements. Then, we allocate an array of properly-aligned dummy structs
1158     // large enough to hold the control block and array. This allows shifting the
1159     // burden of aligning memory properly from us to the allocator.
1160     using _ControlBlock = __unbounded_array_control_block<_Array, _Alloc>;
1161     using _AlignedStorage = __sp_aligned_storage<alignof(_ControlBlock)>;
1162     using _StorageAlloc = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
1163     __allocation_guard<_StorageAlloc> __guard(__a, _ControlBlock::__bytes_for(__n) / sizeof(_AlignedStorage));
1164     _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
1165     std::__construct_at(__control_block, __a, __n, std::forward<_Arg>(__arg)...);
1166     __guard.__release_ptr();
1167     return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
1168 }
1169
1170 template <class _Tp, class _Alloc>
1171 struct __bounded_array_control_block;
1172
1173 template <class _Tp, size_t _Count, class _Alloc>
1174 struct __bounded_array_control_block<_Tp[_Count], _Alloc>
1175     : __shared_weak_count
1176 {
1177     _LIBCPP_HIDE_FROM_ABI constexpr
1178     _Tp* __get_data() noexcept { return __data_; }
1179
1180     _LIBCPP_HIDE_FROM_ABI
1181     explicit __bounded_array_control_block(_Alloc const& __alloc, _Tp const& __arg) : __alloc_(__alloc) {
1182         std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count, __arg);
1183     }
1184
1185     _LIBCPP_HIDE_FROM_ABI
1186     explicit __bounded_array_control_block(_Alloc const& __alloc) : __alloc_(__alloc) {
1187 #if _LIBCPP_STD_VER >= 20
1188         if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
1189             // We are purposefully not using an allocator-aware default construction because the spec says so.
1190             // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
1191             std::uninitialized_default_construct_n(std::addressof(__data_[0]), _Count);
1192         } else {
1193             std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
1194         }
1195 #else
1196         std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
1197 #endif
1198     }
1199
1200     _LIBCPP_HIDE_FROM_ABI_VIRTUAL
1201     ~__bounded_array_control_block() override { } // can't be `= default` because of the sometimes-non-trivial union member __data_
1202
1203 private:
1204     _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
1205 #if _LIBCPP_STD_VER >= 20
1206         if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
1207             std::__reverse_destroy(__data_, __data_ + _Count);
1208         } else {
1209             __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
1210             std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
1211         }
1212 #else
1213         __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
1214         std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
1215 #endif
1216     }
1217
1218     _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
1219         using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, __bounded_array_control_block>;
1220         using _PointerTraits = pointer_traits<typename allocator_traits<_ControlBlockAlloc>::pointer>;
1221
1222         _ControlBlockAlloc __tmp(__alloc_);
1223         __alloc_.~_Alloc();
1224         allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, _PointerTraits::pointer_to(*this), 1);
1225     }
1226
1227     _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
1228     union {
1229         _Tp __data_[_Count];
1230     };
1231 };
1232
1233 template<class _Array, class _Alloc, class... _Arg>
1234 _LIBCPP_HIDE_FROM_ABI
1235 shared_ptr<_Array> __allocate_shared_bounded_array(const _Alloc& __a, _Arg&& ...__arg)
1236 {
1237     static_assert(__libcpp_is_bounded_array<_Array>::value);
1238     using _ControlBlock = __bounded_array_control_block<_Array, _Alloc>;
1239     using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, _ControlBlock>;
1240
1241     __allocation_guard<_ControlBlockAlloc> __guard(__a, 1);
1242     _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
1243     std::__construct_at(__control_block, __a, std::forward<_Arg>(__arg)...);
1244     __guard.__release_ptr();
1245     return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
1246 }
1247
1248 #endif // _LIBCPP_STD_VER >= 17
1249
1250 #if _LIBCPP_STD_VER >= 20
1251
1252 // bounded array variants
1253 template<class _Tp, class _Alloc, class = __enable_if_t<is_bounded_array<_Tp>::value>>
1254 _LIBCPP_HIDE_FROM_ABI
1255 shared_ptr<_Tp> allocate_shared(const _Alloc& __a)
1256 {
1257     return std::__allocate_shared_bounded_array<_Tp>(__a);
1258 }
1259
1260 template<class _Tp, class _Alloc, class = __enable_if_t<is_bounded_array<_Tp>::value>>
1261 _LIBCPP_HIDE_FROM_ABI
1262 shared_ptr<_Tp> allocate_shared(const _Alloc& __a, const remove_extent_t<_Tp>& __u)
1263 {
1264     return std::__allocate_shared_bounded_array<_Tp>(__a, __u);
1265 }
1266
1267 template<class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1268 _LIBCPP_HIDE_FROM_ABI
1269 shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a)
1270 {
1271     using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
1272     _ForOverwriteAllocator __alloc(__a);
1273     return std::__allocate_shared_bounded_array<_Tp>(__alloc);
1274 }
1275
1276 template<class _Tp, class = __enable_if_t<is_bounded_array<_Tp>::value>>
1277 _LIBCPP_HIDE_FROM_ABI
1278 shared_ptr<_Tp> make_shared()
1279 {
1280     return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>());
1281 }
1282
1283 template<class _Tp, class = __enable_if_t<is_bounded_array<_Tp>::value>>
1284 _LIBCPP_HIDE_FROM_ABI
1285 shared_ptr<_Tp> make_shared(const remove_extent_t<_Tp>& __u)
1286 {
1287     return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>(), __u);
1288 }
1289
1290 template<class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1291 _LIBCPP_HIDE_FROM_ABI
1292 shared_ptr<_Tp> make_shared_for_overwrite()
1293 {
1294     return std::__allocate_shared_bounded_array<_Tp>(allocator<__for_overwrite_tag>());
1295 }
1296
1297 // unbounded array variants
1298 template<class _Tp, class _Alloc, class = __enable_if_t<is_unbounded_array<_Tp>::value>>
1299 _LIBCPP_HIDE_FROM_ABI
1300 shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n)
1301 {
1302     return std::__allocate_shared_unbounded_array<_Tp>(__a, __n);
1303 }
1304
1305 template<class _Tp, class _Alloc, class = __enable_if_t<is_unbounded_array<_Tp>::value>>
1306 _LIBCPP_HIDE_FROM_ABI
1307 shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n, const remove_extent_t<_Tp>& __u)
1308 {
1309     return std::__allocate_shared_unbounded_array<_Tp>(__a, __n, __u);
1310 }
1311
1312 template<class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1313 _LIBCPP_HIDE_FROM_ABI
1314 shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a, size_t __n)
1315 {
1316     using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
1317     _ForOverwriteAllocator __alloc(__a);
1318     return std::__allocate_shared_unbounded_array<_Tp>(__alloc, __n);
1319 }
1320
1321 template<class _Tp, class = __enable_if_t<is_unbounded_array<_Tp>::value>>
1322 _LIBCPP_HIDE_FROM_ABI
1323 shared_ptr<_Tp> make_shared(size_t __n)
1324 {
1325     return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n);
1326 }
1327
1328 template<class _Tp, class = __enable_if_t<is_unbounded_array<_Tp>::value>>
1329 _LIBCPP_HIDE_FROM_ABI
1330 shared_ptr<_Tp> make_shared(size_t __n, const remove_extent_t<_Tp>& __u)
1331 {
1332     return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n, __u);
1333 }
1334
1335 template<class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1336 _LIBCPP_HIDE_FROM_ABI
1337 shared_ptr<_Tp> make_shared_for_overwrite(size_t __n)
1338 {
1339     return std::__allocate_shared_unbounded_array<_Tp>(allocator<__for_overwrite_tag>(), __n);
1340 }
1341
1342 #endif // _LIBCPP_STD_VER >= 20
1343
1344 template<class _Tp, class _Up>
1345 inline _LIBCPP_INLINE_VISIBILITY
1346 bool
1347 operator==(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT
1348 {
1349     return __x.get() == __y.get();
1350 }
1351
1352 #if _LIBCPP_STD_VER <= 17
1353
1354 template<class _Tp, class _Up>
1355 inline _LIBCPP_INLINE_VISIBILITY
1356 bool
1357 operator!=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT
1358 {
1359     return !(__x == __y);
1360 }
1361
1362 template<class _Tp, class _Up>
1363 inline _LIBCPP_INLINE_VISIBILITY
1364 bool
1365 operator<(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT
1366 {
1367 #if _LIBCPP_STD_VER <= 11
1368     typedef typename common_type<_Tp*, _Up*>::type _Vp;
1369     return less<_Vp>()(__x.get(), __y.get());
1370 #else
1371     return less<>()(__x.get(), __y.get());
1372 #endif
1373
1374 }
1375
1376 template<class _Tp, class _Up>
1377 inline _LIBCPP_INLINE_VISIBILITY
1378 bool
1379 operator>(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT
1380 {
1381     return __y < __x;
1382 }
1383
1384 template<class _Tp, class _Up>
1385 inline _LIBCPP_INLINE_VISIBILITY
1386 bool
1387 operator<=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT
1388 {
1389     return !(__y < __x);
1390 }
1391
1392 template<class _Tp, class _Up>
1393 inline _LIBCPP_INLINE_VISIBILITY
1394 bool
1395 operator>=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT
1396 {
1397     return !(__x < __y);
1398 }
1399
1400 #endif // _LIBCPP_STD_VER <= 17
1401
1402 #if _LIBCPP_STD_VER >= 20
1403 template<class _Tp, class _Up>
1404 _LIBCPP_HIDE_FROM_ABI strong_ordering
1405 operator<=>(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) noexcept
1406 {
1407     return compare_three_way()(__x.get(), __y.get());
1408 }
1409 #endif
1410
1411 template<class _Tp>
1412 inline _LIBCPP_INLINE_VISIBILITY
1413 bool
1414 operator==(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT
1415 {
1416     return !__x;
1417 }
1418
1419 #if _LIBCPP_STD_VER <= 17
1420
1421 template<class _Tp>
1422 inline _LIBCPP_INLINE_VISIBILITY
1423 bool
1424 operator==(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT
1425 {
1426     return !__x;
1427 }
1428
1429 template<class _Tp>
1430 inline _LIBCPP_INLINE_VISIBILITY
1431 bool
1432 operator!=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT
1433 {
1434     return static_cast<bool>(__x);
1435 }
1436
1437 template<class _Tp>
1438 inline _LIBCPP_INLINE_VISIBILITY
1439 bool
1440 operator!=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT
1441 {
1442     return static_cast<bool>(__x);
1443 }
1444
1445 template<class _Tp>
1446 inline _LIBCPP_INLINE_VISIBILITY
1447 bool
1448 operator<(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT
1449 {
1450     return less<_Tp*>()(__x.get(), nullptr);
1451 }
1452
1453 template<class _Tp>
1454 inline _LIBCPP_INLINE_VISIBILITY
1455 bool
1456 operator<(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT
1457 {
1458     return less<_Tp*>()(nullptr, __x.get());
1459 }
1460
1461 template<class _Tp>
1462 inline _LIBCPP_INLINE_VISIBILITY
1463 bool
1464 operator>(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT
1465 {
1466     return nullptr < __x;
1467 }
1468
1469 template<class _Tp>
1470 inline _LIBCPP_INLINE_VISIBILITY
1471 bool
1472 operator>(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT
1473 {
1474     return __x < nullptr;
1475 }
1476
1477 template<class _Tp>
1478 inline _LIBCPP_INLINE_VISIBILITY
1479 bool
1480 operator<=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT
1481 {
1482     return !(nullptr < __x);
1483 }
1484
1485 template<class _Tp>
1486 inline _LIBCPP_INLINE_VISIBILITY
1487 bool
1488 operator<=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT
1489 {
1490     return !(__x < nullptr);
1491 }
1492
1493 template<class _Tp>
1494 inline _LIBCPP_INLINE_VISIBILITY
1495 bool
1496 operator>=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT
1497 {
1498     return !(__x < nullptr);
1499 }
1500
1501 template<class _Tp>
1502 inline _LIBCPP_INLINE_VISIBILITY
1503 bool
1504 operator>=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT
1505 {
1506     return !(nullptr < __x);
1507 }
1508
1509 #endif // _LIBCPP_STD_VER <= 17
1510
1511 #if _LIBCPP_STD_VER >= 20
1512 template<class _Tp>
1513 _LIBCPP_HIDE_FROM_ABI strong_ordering
1514 operator<=>(shared_ptr<_Tp> const& __x, nullptr_t) noexcept
1515 {
1516     return compare_three_way()(__x.get(), static_cast<typename shared_ptr<_Tp>::element_type*>(nullptr));
1517 }
1518 #endif
1519
1520 template<class _Tp>
1521 inline _LIBCPP_INLINE_VISIBILITY
1522 void
1523 swap(shared_ptr<_Tp>& __x, shared_ptr<_Tp>& __y) _NOEXCEPT
1524 {
1525     __x.swap(__y);
1526 }
1527
1528 template<class _Tp, class _Up>
1529 inline _LIBCPP_INLINE_VISIBILITY
1530 shared_ptr<_Tp>
1531 static_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT
1532 {
1533     return shared_ptr<_Tp>(__r,
1534                            static_cast<
1535                                typename shared_ptr<_Tp>::element_type*>(__r.get()));
1536 }
1537
1538 // LWG-2996
1539 // We don't backport because it is an evolutionary change.
1540 #if _LIBCPP_STD_VER >= 20
1541 template <class _Tp, class _Up>
1542 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1543   return shared_ptr<_Tp>(std::move(__r), static_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1544 }
1545 #endif
1546
1547 template<class _Tp, class _Up>
1548 inline _LIBCPP_INLINE_VISIBILITY
1549 shared_ptr<_Tp>
1550 dynamic_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT
1551 {
1552     typedef typename shared_ptr<_Tp>::element_type _ET;
1553     _ET* __p = dynamic_cast<_ET*>(__r.get());
1554     return __p ? shared_ptr<_Tp>(__r, __p) : shared_ptr<_Tp>();
1555 }
1556
1557 // LWG-2996
1558 // We don't backport because it is an evolutionary change.
1559 #if _LIBCPP_STD_VER >= 20
1560 template <class _Tp, class _Up>
1561 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1562   auto* __p = dynamic_cast<typename shared_ptr<_Tp>::element_type*>(__r.get());
1563   return __p ? shared_ptr<_Tp>(std::move(__r), __p) : shared_ptr<_Tp>();
1564 }
1565 #endif
1566
1567 template<class _Tp, class _Up>
1568 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
1569 const_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT
1570 {
1571     typedef typename shared_ptr<_Tp>::element_type _RTp;
1572     return shared_ptr<_Tp>(__r, const_cast<_RTp*>(__r.get()));
1573 }
1574
1575 // LWG-2996
1576 // We don't backport because it is an evolutionary change.
1577 #if _LIBCPP_STD_VER >= 20
1578 template <class _Tp, class _Up>
1579 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1580   return shared_ptr<_Tp>(std::move(__r), const_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1581 }
1582 #endif
1583
1584 template<class _Tp, class _Up>
1585 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
1586 reinterpret_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT
1587 {
1588     return shared_ptr<_Tp>(__r,
1589                            reinterpret_cast<
1590                                typename shared_ptr<_Tp>::element_type*>(__r.get()));
1591 }
1592
1593 // LWG-2996
1594 // We don't backport because it is an evolutionary change.
1595 #if _LIBCPP_STD_VER >= 20
1596 template <class _Tp, class _Up>
1597 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1598   return shared_ptr<_Tp>(std::move(__r), reinterpret_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1599 }
1600 #endif
1601
1602 #ifndef _LIBCPP_HAS_NO_RTTI
1603
1604 template<class _Dp, class _Tp>
1605 inline _LIBCPP_INLINE_VISIBILITY
1606 _Dp*
1607 get_deleter(const shared_ptr<_Tp>& __p) _NOEXCEPT
1608 {
1609     return __p.template __get_deleter<_Dp>();
1610 }
1611
1612 #endif // _LIBCPP_HAS_NO_RTTI
1613
1614 template<class _Tp>
1615 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS weak_ptr
1616 {
1617 public:
1618 #if _LIBCPP_STD_VER >= 17
1619     typedef remove_extent_t<_Tp> element_type;
1620 #else
1621     typedef _Tp element_type;
1622 #endif
1623
1624 private:
1625     element_type*        __ptr_;
1626     __shared_weak_count* __cntrl_;
1627
1628 public:
1629     _LIBCPP_INLINE_VISIBILITY
1630     _LIBCPP_CONSTEXPR weak_ptr() _NOEXCEPT;
1631
1632     template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1633     _LIBCPP_INLINE_VISIBILITY weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT;
1634
1635     _LIBCPP_INLINE_VISIBILITY
1636     weak_ptr(weak_ptr const& __r) _NOEXCEPT;
1637
1638     template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1639     _LIBCPP_INLINE_VISIBILITY weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT;
1640
1641     _LIBCPP_INLINE_VISIBILITY
1642     weak_ptr(weak_ptr&& __r) _NOEXCEPT;
1643
1644     template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1645     _LIBCPP_INLINE_VISIBILITY weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT;
1646
1647     _LIBCPP_HIDE_FROM_ABI ~weak_ptr();
1648
1649     _LIBCPP_INLINE_VISIBILITY
1650     weak_ptr& operator=(weak_ptr const& __r) _NOEXCEPT;
1651     template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1652     _LIBCPP_INLINE_VISIBILITY weak_ptr&
1653         operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT;
1654
1655     _LIBCPP_INLINE_VISIBILITY
1656     weak_ptr& operator=(weak_ptr&& __r) _NOEXCEPT;
1657     template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1658     _LIBCPP_INLINE_VISIBILITY weak_ptr&
1659         operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT;
1660
1661     template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1662     _LIBCPP_INLINE_VISIBILITY weak_ptr&
1663         operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT;
1664
1665     _LIBCPP_INLINE_VISIBILITY
1666     void swap(weak_ptr& __r) _NOEXCEPT;
1667     _LIBCPP_INLINE_VISIBILITY
1668     void reset() _NOEXCEPT;
1669
1670     _LIBCPP_INLINE_VISIBILITY
1671     long use_count() const _NOEXCEPT
1672         {return __cntrl_ ? __cntrl_->use_count() : 0;}
1673     _LIBCPP_INLINE_VISIBILITY
1674     bool expired() const _NOEXCEPT
1675         {return __cntrl_ == nullptr || __cntrl_->use_count() == 0;}
1676     _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> lock() const _NOEXCEPT;
1677     template<class _Up>
1678         _LIBCPP_INLINE_VISIBILITY
1679         bool owner_before(const shared_ptr<_Up>& __r) const _NOEXCEPT
1680         {return __cntrl_ < __r.__cntrl_;}
1681     template<class _Up>
1682         _LIBCPP_INLINE_VISIBILITY
1683         bool owner_before(const weak_ptr<_Up>& __r) const _NOEXCEPT
1684         {return __cntrl_ < __r.__cntrl_;}
1685
1686     template <class _Up> friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
1687     template <class _Up> friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
1688 };
1689
1690 #if _LIBCPP_STD_VER >= 17
1691 template<class _Tp>
1692 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
1693 #endif
1694
1695 template<class _Tp>
1696 inline
1697 _LIBCPP_CONSTEXPR
1698 weak_ptr<_Tp>::weak_ptr() _NOEXCEPT
1699     : __ptr_(nullptr),
1700       __cntrl_(nullptr)
1701 {
1702 }
1703
1704 template<class _Tp>
1705 inline
1706 weak_ptr<_Tp>::weak_ptr(weak_ptr const& __r) _NOEXCEPT
1707     : __ptr_(__r.__ptr_),
1708       __cntrl_(__r.__cntrl_)
1709 {
1710     if (__cntrl_)
1711         __cntrl_->__add_weak();
1712 }
1713
1714 template<class _Tp>
1715 template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1716 inline
1717 weak_ptr<_Tp>::weak_ptr(shared_ptr<_Yp> const& __r)
1718                          _NOEXCEPT
1719     : __ptr_(__r.__ptr_),
1720       __cntrl_(__r.__cntrl_)
1721 {
1722     if (__cntrl_)
1723         __cntrl_->__add_weak();
1724 }
1725
1726 template<class _Tp>
1727 template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1728 inline
1729 weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp> const& __r)
1730          _NOEXCEPT
1731     : __ptr_(nullptr),
1732       __cntrl_(nullptr)
1733 {
1734     shared_ptr<_Yp> __s = __r.lock();
1735     *this = weak_ptr<_Tp>(__s);
1736 }
1737
1738 template<class _Tp>
1739 inline
1740 weak_ptr<_Tp>::weak_ptr(weak_ptr&& __r) _NOEXCEPT
1741     : __ptr_(__r.__ptr_),
1742       __cntrl_(__r.__cntrl_)
1743 {
1744     __r.__ptr_ = nullptr;
1745     __r.__cntrl_ = nullptr;
1746 }
1747
1748 template<class _Tp>
1749 template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1750 inline
1751 weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp>&& __r)
1752          _NOEXCEPT
1753     : __ptr_(nullptr),
1754       __cntrl_(nullptr)
1755 {
1756     shared_ptr<_Yp> __s = __r.lock();
1757     *this = weak_ptr<_Tp>(__s);
1758     __r.reset();
1759 }
1760
1761 template<class _Tp>
1762 weak_ptr<_Tp>::~weak_ptr()
1763 {
1764     if (__cntrl_)
1765         __cntrl_->__release_weak();
1766 }
1767
1768 template<class _Tp>
1769 inline
1770 weak_ptr<_Tp>&
1771 weak_ptr<_Tp>::operator=(weak_ptr const& __r) _NOEXCEPT
1772 {
1773     weak_ptr(__r).swap(*this);
1774     return *this;
1775 }
1776
1777 template<class _Tp>
1778 template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1779 inline
1780 weak_ptr<_Tp>&
1781 weak_ptr<_Tp>::operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT
1782 {
1783     weak_ptr(__r).swap(*this);
1784     return *this;
1785 }
1786
1787 template<class _Tp>
1788 inline
1789 weak_ptr<_Tp>&
1790 weak_ptr<_Tp>::operator=(weak_ptr&& __r) _NOEXCEPT
1791 {
1792     weak_ptr(_VSTD::move(__r)).swap(*this);
1793     return *this;
1794 }
1795
1796 template<class _Tp>
1797 template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1798 inline
1799 weak_ptr<_Tp>&
1800 weak_ptr<_Tp>::operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT
1801 {
1802     weak_ptr(_VSTD::move(__r)).swap(*this);
1803     return *this;
1804 }
1805
1806 template<class _Tp>
1807 template<class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1808 inline
1809 weak_ptr<_Tp>&
1810 weak_ptr<_Tp>::operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT
1811 {
1812     weak_ptr(__r).swap(*this);
1813     return *this;
1814 }
1815
1816 template<class _Tp>
1817 inline
1818 void
1819 weak_ptr<_Tp>::swap(weak_ptr& __r) _NOEXCEPT
1820 {
1821     _VSTD::swap(__ptr_, __r.__ptr_);
1822     _VSTD::swap(__cntrl_, __r.__cntrl_);
1823 }
1824
1825 template<class _Tp>
1826 inline _LIBCPP_INLINE_VISIBILITY
1827 void
1828 swap(weak_ptr<_Tp>& __x, weak_ptr<_Tp>& __y) _NOEXCEPT
1829 {
1830     __x.swap(__y);
1831 }
1832
1833 template<class _Tp>
1834 inline
1835 void
1836 weak_ptr<_Tp>::reset() _NOEXCEPT
1837 {
1838     weak_ptr().swap(*this);
1839 }
1840
1841 template<class _Tp>
1842 shared_ptr<_Tp>
1843 weak_ptr<_Tp>::lock() const _NOEXCEPT
1844 {
1845     shared_ptr<_Tp> __r;
1846     __r.__cntrl_ = __cntrl_ ? __cntrl_->lock() : __cntrl_;
1847     if (__r.__cntrl_)
1848         __r.__ptr_ = __ptr_;
1849     return __r;
1850 }
1851
1852 #if _LIBCPP_STD_VER >= 17
1853 template <class _Tp = void> struct owner_less;
1854 #else
1855 template <class _Tp> struct owner_less;
1856 #endif
1857
1858
1859 template <class _Tp>
1860 struct _LIBCPP_TEMPLATE_VIS owner_less<shared_ptr<_Tp> >
1861     : __binary_function<shared_ptr<_Tp>, shared_ptr<_Tp>, bool>
1862 {
1863     _LIBCPP_INLINE_VISIBILITY
1864     bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT
1865         {return __x.owner_before(__y);}
1866     _LIBCPP_INLINE_VISIBILITY
1867     bool operator()(shared_ptr<_Tp> const& __x,   weak_ptr<_Tp> const& __y) const _NOEXCEPT
1868         {return __x.owner_before(__y);}
1869     _LIBCPP_INLINE_VISIBILITY
1870     bool operator()(  weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT
1871         {return __x.owner_before(__y);}
1872 };
1873
1874 template <class _Tp>
1875 struct _LIBCPP_TEMPLATE_VIS owner_less<weak_ptr<_Tp> >
1876     : __binary_function<weak_ptr<_Tp>, weak_ptr<_Tp>, bool>
1877 {
1878     _LIBCPP_INLINE_VISIBILITY
1879     bool operator()(  weak_ptr<_Tp> const& __x,   weak_ptr<_Tp> const& __y) const _NOEXCEPT
1880         {return __x.owner_before(__y);}
1881     _LIBCPP_INLINE_VISIBILITY
1882     bool operator()(shared_ptr<_Tp> const& __x,   weak_ptr<_Tp> const& __y) const _NOEXCEPT
1883         {return __x.owner_before(__y);}
1884     _LIBCPP_INLINE_VISIBILITY
1885     bool operator()(  weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT
1886         {return __x.owner_before(__y);}
1887 };
1888
1889 #if _LIBCPP_STD_VER >= 17
1890 template <>
1891 struct _LIBCPP_TEMPLATE_VIS owner_less<void>
1892 {
1893     template <class _Tp, class _Up>
1894     _LIBCPP_INLINE_VISIBILITY
1895     bool operator()( shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT
1896         {return __x.owner_before(__y);}
1897     template <class _Tp, class _Up>
1898     _LIBCPP_INLINE_VISIBILITY
1899     bool operator()( shared_ptr<_Tp> const& __x,   weak_ptr<_Up> const& __y) const _NOEXCEPT
1900         {return __x.owner_before(__y);}
1901     template <class _Tp, class _Up>
1902     _LIBCPP_INLINE_VISIBILITY
1903     bool operator()(   weak_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT
1904         {return __x.owner_before(__y);}
1905     template <class _Tp, class _Up>
1906     _LIBCPP_INLINE_VISIBILITY
1907     bool operator()(   weak_ptr<_Tp> const& __x,   weak_ptr<_Up> const& __y) const _NOEXCEPT
1908         {return __x.owner_before(__y);}
1909     typedef void is_transparent;
1910 };
1911 #endif
1912
1913 template<class _Tp>
1914 class _LIBCPP_TEMPLATE_VIS enable_shared_from_this
1915 {
1916     mutable weak_ptr<_Tp> __weak_this_;
1917 protected:
1918     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
1919     enable_shared_from_this() _NOEXCEPT {}
1920     _LIBCPP_INLINE_VISIBILITY
1921     enable_shared_from_this(enable_shared_from_this const&) _NOEXCEPT {}
1922     _LIBCPP_INLINE_VISIBILITY
1923     enable_shared_from_this& operator=(enable_shared_from_this const&) _NOEXCEPT
1924         {return *this;}
1925     _LIBCPP_INLINE_VISIBILITY
1926     ~enable_shared_from_this() {}
1927 public:
1928     _LIBCPP_INLINE_VISIBILITY
1929     shared_ptr<_Tp> shared_from_this()
1930         {return shared_ptr<_Tp>(__weak_this_);}
1931     _LIBCPP_INLINE_VISIBILITY
1932     shared_ptr<_Tp const> shared_from_this() const
1933         {return shared_ptr<const _Tp>(__weak_this_);}
1934
1935 #if _LIBCPP_STD_VER >= 17
1936     _LIBCPP_INLINE_VISIBILITY
1937     weak_ptr<_Tp> weak_from_this() _NOEXCEPT
1938        { return __weak_this_; }
1939
1940     _LIBCPP_INLINE_VISIBILITY
1941     weak_ptr<const _Tp> weak_from_this() const _NOEXCEPT
1942         { return __weak_this_; }
1943 #endif // _LIBCPP_STD_VER >= 17
1944
1945     template <class _Up> friend class shared_ptr;
1946 };
1947
1948 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS hash;
1949
1950 template <class _Tp>
1951 struct _LIBCPP_TEMPLATE_VIS hash<shared_ptr<_Tp> >
1952 {
1953 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_BINDER_TYPEDEFS)
1954     _LIBCPP_DEPRECATED_IN_CXX17 typedef shared_ptr<_Tp> argument_type;
1955     _LIBCPP_DEPRECATED_IN_CXX17 typedef size_t          result_type;
1956 #endif
1957
1958     _LIBCPP_INLINE_VISIBILITY
1959     size_t operator()(const shared_ptr<_Tp>& __ptr) const _NOEXCEPT
1960     {
1961         return hash<typename shared_ptr<_Tp>::element_type*>()(__ptr.get());
1962     }
1963 };
1964
1965 template<class _CharT, class _Traits, class _Yp>
1966 inline _LIBCPP_INLINE_VISIBILITY
1967 basic_ostream<_CharT, _Traits>&
1968 operator<<(basic_ostream<_CharT, _Traits>& __os, shared_ptr<_Yp> const& __p);
1969
1970
1971 #if !defined(_LIBCPP_HAS_NO_THREADS)
1972
1973 class _LIBCPP_EXPORTED_FROM_ABI __sp_mut
1974 {
1975     void* __lx_;
1976 public:
1977     void lock() _NOEXCEPT;
1978     void unlock() _NOEXCEPT;
1979
1980 private:
1981     _LIBCPP_CONSTEXPR __sp_mut(void*) _NOEXCEPT;
1982     __sp_mut(const __sp_mut&);
1983     __sp_mut& operator=(const __sp_mut&);
1984
1985     friend _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
1986 };
1987
1988 _LIBCPP_EXPORTED_FROM_ABI _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
1989 __sp_mut& __get_sp_mut(const void*);
1990
1991 template <class _Tp>
1992 inline _LIBCPP_INLINE_VISIBILITY
1993 bool
1994 atomic_is_lock_free(const shared_ptr<_Tp>*)
1995 {
1996     return false;
1997 }
1998
1999 template <class _Tp>
2000 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2001 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
2002 atomic_load(const shared_ptr<_Tp>* __p)
2003 {
2004     __sp_mut& __m = std::__get_sp_mut(__p);
2005     __m.lock();
2006     shared_ptr<_Tp> __q = *__p;
2007     __m.unlock();
2008     return __q;
2009 }
2010
2011 template <class _Tp>
2012 inline _LIBCPP_INLINE_VISIBILITY
2013 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2014 shared_ptr<_Tp>
2015 atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order)
2016 {
2017     return std::atomic_load(__p);
2018 }
2019
2020 template <class _Tp>
2021 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2022 _LIBCPP_HIDE_FROM_ABI void
2023 atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
2024 {
2025     __sp_mut& __m = std::__get_sp_mut(__p);
2026     __m.lock();
2027     __p->swap(__r);
2028     __m.unlock();
2029 }
2030
2031 template <class _Tp>
2032 inline _LIBCPP_INLINE_VISIBILITY
2033 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2034 void
2035 atomic_store_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order)
2036 {
2037     std::atomic_store(__p, __r);
2038 }
2039
2040 template <class _Tp>
2041 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2042 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
2043 atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
2044 {
2045     __sp_mut& __m = std::__get_sp_mut(__p);
2046     __m.lock();
2047     __p->swap(__r);
2048     __m.unlock();
2049     return __r;
2050 }
2051
2052 template <class _Tp>
2053 inline _LIBCPP_INLINE_VISIBILITY
2054 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2055 shared_ptr<_Tp>
2056 atomic_exchange_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order)
2057 {
2058     return std::atomic_exchange(__p, __r);
2059 }
2060
2061 template <class _Tp>
2062 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2063 _LIBCPP_HIDE_FROM_ABI bool
2064 atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w)
2065 {
2066     shared_ptr<_Tp> __temp;
2067     __sp_mut& __m = std::__get_sp_mut(__p);
2068     __m.lock();
2069     if (__p->__owner_equivalent(*__v))
2070     {
2071         _VSTD::swap(__temp, *__p);
2072         *__p = __w;
2073         __m.unlock();
2074         return true;
2075     }
2076     _VSTD::swap(__temp, *__v);
2077     *__v = *__p;
2078     __m.unlock();
2079     return false;
2080 }
2081
2082 template <class _Tp>
2083 inline _LIBCPP_INLINE_VISIBILITY
2084 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2085 bool
2086 atomic_compare_exchange_weak(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w)
2087 {
2088     return std::atomic_compare_exchange_strong(__p, __v, __w);
2089 }
2090
2091 template <class _Tp>
2092 inline _LIBCPP_INLINE_VISIBILITY
2093 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2094 bool
2095 atomic_compare_exchange_strong_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v,
2096                                         shared_ptr<_Tp> __w, memory_order, memory_order)
2097 {
2098     return std::atomic_compare_exchange_strong(__p, __v, __w);
2099 }
2100
2101 template <class _Tp>
2102 inline _LIBCPP_INLINE_VISIBILITY
2103 _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR
2104 bool
2105 atomic_compare_exchange_weak_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v,
2106                                       shared_ptr<_Tp> __w, memory_order, memory_order)
2107 {
2108     return std::atomic_compare_exchange_weak(__p, __v, __w);
2109 }
2110
2111 #endif // !defined(_LIBCPP_HAS_NO_THREADS)
2112
2113 _LIBCPP_END_NAMESPACE_STD
2114
2115 #endif // _LIBCPP___MEMORY_SHARED_PTR_H