xref: /freebsd/contrib/llvm-project/libcxx/include/__memory/shared_ptr.h (revision 0fca6ea1d4eea4c934cfff25ac9ee8ad6fe95583) 
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 <__exception/exception.h>
17 #include <__functional/binary_function.h>
18 #include <__functional/operations.h>
19 #include <__functional/reference_wrapper.h>
20 #include <__fwd/ostream.h>
21 #include <__iterator/access.h>
22 #include <__memory/addressof.h>
23 #include <__memory/allocation_guard.h>
24 #include <__memory/allocator.h>
25 #include <__memory/allocator_destructor.h>
26 #include <__memory/allocator_traits.h>
27 #include <__memory/auto_ptr.h>
28 #include <__memory/compressed_pair.h>
29 #include <__memory/construct_at.h>
30 #include <__memory/pointer_traits.h>
31 #include <__memory/uninitialized_algorithms.h>
32 #include <__memory/unique_ptr.h>
33 #include <__type_traits/add_lvalue_reference.h>
34 #include <__type_traits/conditional.h>
35 #include <__type_traits/conjunction.h>
36 #include <__type_traits/disjunction.h>
37 #include <__type_traits/is_array.h>
38 #include <__type_traits/is_bounded_array.h>
39 #include <__type_traits/is_constructible.h>
40 #include <__type_traits/is_convertible.h>
41 #include <__type_traits/is_reference.h>
42 #include <__type_traits/is_unbounded_array.h>
43 #include <__type_traits/nat.h>
44 #include <__type_traits/negation.h>
45 #include <__type_traits/remove_extent.h>
46 #include <__type_traits/remove_reference.h>
47 #include <__utility/declval.h>
48 #include <__utility/forward.h>
49 #include <__utility/move.h>
50 #include <__utility/swap.h>
51 #include <__verbose_abort>
52 #include <cstddef>
53 #include <new>
54 #include <typeinfo>
55 #if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
56 #  include <__atomic/memory_order.h>
57 #endif
58 
59 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
60 #  pragma GCC system_header
61 #endif
62 
63 _LIBCPP_PUSH_MACROS
64 #include <__undef_macros>
65 
66 _LIBCPP_BEGIN_NAMESPACE_STD
67 
68 // NOTE: Relaxed and acq/rel atomics (for increment and decrement respectively)
69 // should be sufficient for thread safety.
70 // See https://llvm.org/PR22803
71 #if defined(__clang__) && __has_builtin(__atomic_add_fetch) && defined(__ATOMIC_RELAXED) && 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>
__libcpp_relaxed_load(_ValueType const * __value)78 inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_relaxed_load(_ValueType const* __value) {
79 #if !defined(_LIBCPP_HAS_NO_THREADS) && defined(__ATOMIC_RELAXED) &&                                                   \
80     (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
81   return __atomic_load_n(__value, __ATOMIC_RELAXED);
82 #else
83   return *__value;
84 #endif
85 }
86 
87 template <class _ValueType>
__libcpp_acquire_load(_ValueType const * __value)88 inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_acquire_load(_ValueType const* __value) {
89 #if !defined(_LIBCPP_HAS_NO_THREADS) && defined(__ATOMIC_ACQUIRE) &&                                                   \
90     (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
91   return __atomic_load_n(__value, __ATOMIC_ACQUIRE);
92 #else
93   return *__value;
94 #endif
95 }
96 
97 template <class _Tp>
__libcpp_atomic_refcount_increment(_Tp & __t)98 inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_increment(_Tp& __t) _NOEXCEPT {
99 #if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && !defined(_LIBCPP_HAS_NO_THREADS)
100   return __atomic_add_fetch(&__t, 1, __ATOMIC_RELAXED);
101 #else
102   return __t += 1;
103 #endif
104 }
105 
106 template <class _Tp>
__libcpp_atomic_refcount_decrement(_Tp & __t)107 inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_decrement(_Tp& __t) _NOEXCEPT {
108 #if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && !defined(_LIBCPP_HAS_NO_THREADS)
109   return __atomic_add_fetch(&__t, -1, __ATOMIC_ACQ_REL);
110 #else
111   return __t -= 1;
112 #endif
113 }
114 
115 class _LIBCPP_EXPORTED_FROM_ABI bad_weak_ptr : public std::exception {
116 public:
117   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr() _NOEXCEPT                               = default;
118   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr(const bad_weak_ptr&) _NOEXCEPT            = default;
119   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr& operator=(const bad_weak_ptr&) _NOEXCEPT = default;
120   ~bad_weak_ptr() _NOEXCEPT override;
121   const char* what() const _NOEXCEPT override;
122 };
123 
__throw_bad_weak_ptr()124 _LIBCPP_NORETURN inline _LIBCPP_HIDE_FROM_ABI void __throw_bad_weak_ptr() {
125 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
126   throw bad_weak_ptr();
127 #else
128   _LIBCPP_VERBOSE_ABORT("bad_weak_ptr was thrown in -fno-exceptions mode");
129 #endif
130 }
131 
132 template <class _Tp>
133 class _LIBCPP_TEMPLATE_VIS weak_ptr;
134 
135 class _LIBCPP_EXPORTED_FROM_ABI __shared_count {
136   __shared_count(const __shared_count&);
137   __shared_count& operator=(const __shared_count&);
138 
139 protected:
140   long __shared_owners_;
141   virtual ~__shared_count();
142 
143 private:
144   virtual void __on_zero_shared() _NOEXCEPT = 0;
145 
146 public:
__shared_owners_(__refs)147   _LIBCPP_HIDE_FROM_ABI explicit __shared_count(long __refs = 0) _NOEXCEPT : __shared_owners_(__refs) {}
148 
149 #if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
150   void __add_shared() noexcept;
151   bool __release_shared() noexcept;
152 #else
__add_shared()153   _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_owners_); }
__release_shared()154   _LIBCPP_HIDE_FROM_ABI bool __release_shared() _NOEXCEPT {
155     if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {
156       __on_zero_shared();
157       return true;
158     }
159     return false;
160   }
161 #endif
use_count()162   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __libcpp_relaxed_load(&__shared_owners_) + 1; }
163 };
164 
165 class _LIBCPP_EXPORTED_FROM_ABI __shared_weak_count : private __shared_count {
166   long __shared_weak_owners_;
167 
168 public:
169   _LIBCPP_HIDE_FROM_ABI explicit __shared_weak_count(long __refs = 0) _NOEXCEPT
__shared_count(__refs)170       : __shared_count(__refs),
171         __shared_weak_owners_(__refs) {}
172 
173 protected:
174   ~__shared_weak_count() override;
175 
176 public:
177 #if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
178   void __add_shared() noexcept;
179   void __add_weak() noexcept;
180   void __release_shared() noexcept;
181 #else
182   _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __shared_count::__add_shared(); }
183   _LIBCPP_HIDE_FROM_ABI void __add_weak() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_weak_owners_); }
184   _LIBCPP_HIDE_FROM_ABI void __release_shared() _NOEXCEPT {
185     if (__shared_count::__release_shared())
186       __release_weak();
187   }
188 #endif
189   void __release_weak() _NOEXCEPT;
use_count()190   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __shared_count::use_count(); }
191   __shared_weak_count* lock() _NOEXCEPT;
192 
193   virtual const void* __get_deleter(const type_info&) const _NOEXCEPT;
194 
195 private:
196   virtual void __on_zero_shared_weak() _NOEXCEPT = 0;
197 };
198 
199 template <class _Tp, class _Dp, class _Alloc>
200 class __shared_ptr_pointer : public __shared_weak_count {
201   __compressed_pair<__compressed_pair<_Tp, _Dp>, _Alloc> __data_;
202 
203 public:
__shared_ptr_pointer(_Tp __p,_Dp __d,_Alloc __a)204   _LIBCPP_HIDE_FROM_ABI __shared_ptr_pointer(_Tp __p, _Dp __d, _Alloc __a)
205       : __data_(__compressed_pair<_Tp, _Dp>(__p, std::move(__d)), std::move(__a)) {}
206 
207 #ifndef _LIBCPP_HAS_NO_RTTI
208   _LIBCPP_HIDE_FROM_ABI_VIRTUAL const void* __get_deleter(const type_info&) const _NOEXCEPT override;
209 #endif
210 
211 private:
212   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override;
213   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override;
214 };
215 
216 #ifndef _LIBCPP_HAS_NO_RTTI
217 
218 template <class _Tp, class _Dp, class _Alloc>
__get_deleter(const type_info & __t)219 const void* __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__get_deleter(const type_info& __t) const _NOEXCEPT {
220   return __t == typeid(_Dp) ? std::addressof(__data_.first().second()) : nullptr;
221 }
222 
223 #endif // _LIBCPP_HAS_NO_RTTI
224 
225 template <class _Tp, class _Dp, class _Alloc>
__on_zero_shared()226 void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared() _NOEXCEPT {
227   __data_.first().second()(__data_.first().first());
228   __data_.first().second().~_Dp();
229 }
230 
231 template <class _Tp, class _Dp, class _Alloc>
__on_zero_shared_weak()232 void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared_weak() _NOEXCEPT {
233   typedef typename __allocator_traits_rebind<_Alloc, __shared_ptr_pointer>::type _Al;
234   typedef allocator_traits<_Al> _ATraits;
235   typedef pointer_traits<typename _ATraits::pointer> _PTraits;
236 
237   _Al __a(__data_.second());
238   __data_.second().~_Alloc();
239   __a.deallocate(_PTraits::pointer_to(*this), 1);
240 }
241 
242 // This tag is used to instantiate an allocator type. The various shared_ptr control blocks
243 // detect that the allocator has been instantiated for this type and perform alternative
244 // initialization/destruction based on that.
245 struct __for_overwrite_tag {};
246 
247 template <class _Tp, class _Alloc>
248 struct __shared_ptr_emplace : __shared_weak_count {
249   template <class... _Args,
250             class _Allocator                                                                         = _Alloc,
251             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
__shared_ptr_emplace__shared_ptr_emplace252   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&...) : __storage_(std::move(__a)) {
253     static_assert(
254         sizeof...(_Args) == 0, "No argument should be provided to the control block when using _for_overwrite");
255     ::new ((void*)__get_elem()) _Tp;
256   }
257 
258   template <class... _Args,
259             class _Allocator                                                                          = _Alloc,
260             __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
__shared_ptr_emplace__shared_ptr_emplace261   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&... __args) : __storage_(std::move(__a)) {
262     using _TpAlloc = typename __allocator_traits_rebind<_Alloc, __remove_cv_t<_Tp> >::type;
263     _TpAlloc __tmp(*__get_alloc());
264     allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), std::forward<_Args>(__args)...);
265   }
266 
__get_alloc__shared_ptr_emplace267   _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT { return __storage_.__get_alloc(); }
268 
__get_elem__shared_ptr_emplace269   _LIBCPP_HIDE_FROM_ABI _Tp* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }
270 
271 private:
272   template <class _Allocator                                                                         = _Alloc,
273             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
__on_zero_shared_impl__shared_ptr_emplace274   _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
275     __get_elem()->~_Tp();
276   }
277 
278   template <class _Allocator                                                                          = _Alloc,
279             __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
__on_zero_shared_impl__shared_ptr_emplace280   _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
281     using _TpAlloc = typename __allocator_traits_rebind<_Allocator, __remove_cv_t<_Tp> >::type;
282     _TpAlloc __tmp(*__get_alloc());
283     allocator_traits<_TpAlloc>::destroy(__tmp, __get_elem());
284   }
285 
__on_zero_shared__shared_ptr_emplace286   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override { __on_zero_shared_impl(); }
287 
__on_zero_shared_weak__shared_ptr_emplace288   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
289     using _ControlBlockAlloc   = typename __allocator_traits_rebind<_Alloc, __shared_ptr_emplace>::type;
290     using _ControlBlockPointer = typename allocator_traits<_ControlBlockAlloc>::pointer;
291     _ControlBlockAlloc __tmp(*__get_alloc());
292     __storage_.~_Storage();
293     allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, pointer_traits<_ControlBlockPointer>::pointer_to(*this), 1);
294   }
295 
296   // This class implements the control block for non-array shared pointers created
297   // through `std::allocate_shared` and `std::make_shared`.
298   //
299   // In previous versions of the library, we used a compressed pair to store
300   // both the _Alloc and the _Tp. This implies using EBO, which is incompatible
301   // with Allocator construction for _Tp. To allow implementing P0674 in C++20,
302   // we now use a properly aligned char buffer while making sure that we maintain
303   // the same layout that we had when we used a compressed pair.
304   using _CompressedPair = __compressed_pair<_Alloc, _Tp>;
_ALIGNAS_TYPE__shared_ptr_emplace305   struct _ALIGNAS_TYPE(_CompressedPair) _Storage {
306     char __blob_[sizeof(_CompressedPair)];
307 
308     _LIBCPP_HIDE_FROM_ABI explicit _Storage(_Alloc&& __a) { ::new ((void*)__get_alloc()) _Alloc(std::move(__a)); }
309     _LIBCPP_HIDE_FROM_ABI ~_Storage() { __get_alloc()->~_Alloc(); }
310     _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT {
311       _CompressedPair* __as_pair                = reinterpret_cast<_CompressedPair*>(__blob_);
312       typename _CompressedPair::_Base1* __first = _CompressedPair::__get_first_base(__as_pair);
313       _Alloc* __alloc                           = reinterpret_cast<_Alloc*>(__first);
314       return __alloc;
315     }
316     _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _Tp* __get_elem() _NOEXCEPT {
317       _CompressedPair* __as_pair                 = reinterpret_cast<_CompressedPair*>(__blob_);
318       typename _CompressedPair::_Base2* __second = _CompressedPair::__get_second_base(__as_pair);
319       _Tp* __elem                                = reinterpret_cast<_Tp*>(__second);
320       return __elem;
321     }
322   };
323 
324   static_assert(_LIBCPP_ALIGNOF(_Storage) == _LIBCPP_ALIGNOF(_CompressedPair), "");
325   static_assert(sizeof(_Storage) == sizeof(_CompressedPair), "");
326   _Storage __storage_;
327 };
328 
329 struct __shared_ptr_dummy_rebind_allocator_type;
330 template <>
331 class _LIBCPP_TEMPLATE_VIS allocator<__shared_ptr_dummy_rebind_allocator_type> {
332 public:
333   template <class _Other>
334   struct rebind {
335     typedef allocator<_Other> other;
336   };
337 };
338 
339 template <class _Tp>
340 class _LIBCPP_TEMPLATE_VIS enable_shared_from_this;
341 
342 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.general-6
343 // A pointer type Y* is said to be compatible with a pointer type T*
344 // when either Y* is convertible to T* or Y is U[N] and T is cv U[].
345 #if _LIBCPP_STD_VER >= 17
346 template <class _Yp, class _Tp>
347 struct __bounded_convertible_to_unbounded : false_type {};
348 
349 template <class _Up, std::size_t _Np, class _Tp>
350 struct __bounded_convertible_to_unbounded<_Up[_Np], _Tp> : is_same<__remove_cv_t<_Tp>, _Up[]> {};
351 
352 template <class _Yp, class _Tp>
353 struct __compatible_with : _Or< is_convertible<_Yp*, _Tp*>, __bounded_convertible_to_unbounded<_Yp, _Tp> > {};
354 #else
355 template <class _Yp, class _Tp>
356 struct __compatible_with : is_convertible<_Yp*, _Tp*> {};
357 #endif // _LIBCPP_STD_VER >= 17
358 
359 // Constructors that take raw pointers have a different set of "compatible" constraints
360 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.const-9.1
361 // - If T is an array type, then either T is U[N] and Y(*)[N] is convertible to T*,
362 //   or T is U[] and Y(*)[] is convertible to T*.
363 // - If T is not an array type, then Y* is convertible to T*.
364 #if _LIBCPP_STD_VER >= 17
365 template <class _Yp, class _Tp, class = void>
366 struct __raw_pointer_compatible_with : _And< _Not<is_array<_Tp>>, is_convertible<_Yp*, _Tp*> > {};
367 
368 template <class _Yp, class _Up, std::size_t _Np>
369 struct __raw_pointer_compatible_with<_Yp, _Up[_Np], __enable_if_t< is_convertible<_Yp (*)[_Np], _Up (*)[_Np]>::value> >
370     : true_type {};
371 
372 template <class _Yp, class _Up>
373 struct __raw_pointer_compatible_with<_Yp, _Up[], __enable_if_t< is_convertible<_Yp (*)[], _Up (*)[]>::value> >
374     : true_type {};
375 
376 #else
377 template <class _Yp, class _Tp>
378 struct __raw_pointer_compatible_with : is_convertible<_Yp*, _Tp*> {};
379 #endif // _LIBCPP_STD_VER >= 17
380 
381 template <class _Ptr, class = void>
382 struct __is_deletable : false_type {};
383 template <class _Ptr>
384 struct __is_deletable<_Ptr, decltype(delete std::declval<_Ptr>())> : true_type {};
385 
386 template <class _Ptr, class = void>
387 struct __is_array_deletable : false_type {};
388 template <class _Ptr>
389 struct __is_array_deletable<_Ptr, decltype(delete[] std::declval<_Ptr>())> : true_type {};
390 
391 template <class _Dp, class _Pt, class = decltype(std::declval<_Dp>()(std::declval<_Pt>()))>
392 true_type __well_formed_deleter_test(int);
393 
394 template <class, class>
395 false_type __well_formed_deleter_test(...);
396 
397 template <class _Dp, class _Pt>
398 struct __well_formed_deleter : decltype(std::__well_formed_deleter_test<_Dp, _Pt>(0)) {};
399 
400 template <class _Dp, class _Yp, class _Tp>
401 struct __shared_ptr_deleter_ctor_reqs {
402   static const bool value = __raw_pointer_compatible_with<_Yp, _Tp>::value && is_move_constructible<_Dp>::value &&
403                             __well_formed_deleter<_Dp, _Yp*>::value;
404 };
405 
406 template <class _Dp>
407 using __shared_ptr_nullptr_deleter_ctor_reqs = _And<is_move_constructible<_Dp>, __well_formed_deleter<_Dp, nullptr_t> >;
408 
409 #if defined(_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI)
410 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI __attribute__((__trivial_abi__))
411 #else
412 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI
413 #endif
414 
415 template <class _Tp>
416 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS shared_ptr {
417   struct __nullptr_sfinae_tag {};
418 
419 public:
420 #if _LIBCPP_STD_VER >= 17
421   typedef weak_ptr<_Tp> weak_type;
422   typedef remove_extent_t<_Tp> element_type;
423 #else
424   typedef _Tp element_type;
425 #endif
426 
427   // A shared_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
428   // any bookkeeping, so it's always trivially relocatable.
429   using __trivially_relocatable = shared_ptr;
430 
431 private:
432   element_type* __ptr_;
433   __shared_weak_count* __cntrl_;
434 
435 public:
436   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
437 
438   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr(nullptr_t) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
439 
440   template <class _Yp,
441             __enable_if_t< _And< __raw_pointer_compatible_with<_Yp, _Tp>
442   // In C++03 we get errors when trying to do SFINAE with the
443   // delete operator, so we always pretend that it's deletable.
444   // The same happens on GCC.
445 #if !defined(_LIBCPP_CXX03_LANG) && !defined(_LIBCPP_COMPILER_GCC)
446                                  ,
447                                  _If<is_array<_Tp>::value, __is_array_deletable<_Yp*>, __is_deletable<_Yp*> >
448 #endif
449                                  >::value,
450                            int> = 0>
451   _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(_Yp* __p) : __ptr_(__p) {
452     unique_ptr<_Yp> __hold(__p);
453     typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
454     typedef __shared_ptr_pointer<_Yp*, __shared_ptr_default_delete<_Tp, _Yp>, _AllocT> _CntrlBlk;
455     __cntrl_ = new _CntrlBlk(__p, __shared_ptr_default_delete<_Tp, _Yp>(), _AllocT());
456     __hold.release();
457     __enable_weak_this(__p, __p);
458   }
459 
460   template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
461   _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d) : __ptr_(__p) {
462 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
463     try {
464 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
465       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
466       typedef __shared_ptr_pointer<_Yp*, _Dp, _AllocT> _CntrlBlk;
467 #ifndef _LIBCPP_CXX03_LANG
468       __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
469 #else
470     __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
471 #endif // not _LIBCPP_CXX03_LANG
472       __enable_weak_this(__p, __p);
473 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
474     } catch (...) {
475       __d(__p);
476       throw;
477     }
478 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
479   }
480 
481   template <class _Yp,
482             class _Dp,
483             class _Alloc,
484             __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
485   _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d, _Alloc __a) : __ptr_(__p) {
486 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
487     try {
488 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
489       typedef __shared_ptr_pointer<_Yp*, _Dp, _Alloc> _CntrlBlk;
490       typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
491       typedef __allocator_destructor<_A2> _D2;
492       _A2 __a2(__a);
493       unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
494       ::new ((void*)std::addressof(*__hold2.get()))
495 #ifndef _LIBCPP_CXX03_LANG
496           _CntrlBlk(__p, std::move(__d), __a);
497 #else
498         _CntrlBlk(__p, __d, __a);
499 #endif // not _LIBCPP_CXX03_LANG
500       __cntrl_ = std::addressof(*__hold2.release());
501       __enable_weak_this(__p, __p);
502 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
503     } catch (...) {
504       __d(__p);
505       throw;
506     }
507 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
508   }
509 
510   template <class _Dp>
511   _LIBCPP_HIDE_FROM_ABI shared_ptr(
512       nullptr_t __p,
513       _Dp __d,
514       __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs<_Dp>::value, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
515       : __ptr_(nullptr) {
516 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
517     try {
518 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
519       typedef typename __shared_ptr_default_allocator<_Tp>::type _AllocT;
520       typedef __shared_ptr_pointer<nullptr_t, _Dp, _AllocT> _CntrlBlk;
521 #ifndef _LIBCPP_CXX03_LANG
522       __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
523 #else
524     __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
525 #endif // not _LIBCPP_CXX03_LANG
526 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
527     } catch (...) {
528       __d(__p);
529       throw;
530     }
531 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
532   }
533 
534   template <class _Dp, class _Alloc>
535   _LIBCPP_HIDE_FROM_ABI shared_ptr(
536       nullptr_t __p,
537       _Dp __d,
538       _Alloc __a,
539       __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs<_Dp>::value, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
540       : __ptr_(nullptr) {
541 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
542     try {
543 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
544       typedef __shared_ptr_pointer<nullptr_t, _Dp, _Alloc> _CntrlBlk;
545       typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
546       typedef __allocator_destructor<_A2> _D2;
547       _A2 __a2(__a);
548       unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
549       ::new ((void*)std::addressof(*__hold2.get()))
550 #ifndef _LIBCPP_CXX03_LANG
551           _CntrlBlk(__p, std::move(__d), __a);
552 #else
553         _CntrlBlk(__p, __d, __a);
554 #endif // not _LIBCPP_CXX03_LANG
555       __cntrl_ = std::addressof(*__hold2.release());
556 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
557     } catch (...) {
558       __d(__p);
559       throw;
560     }
561 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
562   }
563 
564   template <class _Yp>
565   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) _NOEXCEPT
566       : __ptr_(__p),
567         __cntrl_(__r.__cntrl_) {
568     if (__cntrl_)
569       __cntrl_->__add_shared();
570   }
571 
572 // LWG-2996
573 // We don't backport because it is an evolutionary change.
574 #if _LIBCPP_STD_VER >= 20
575   template <class _Yp>
576   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
577       : __ptr_(__p), __cntrl_(__r.__cntrl_) {
578     __r.__ptr_   = nullptr;
579     __r.__cntrl_ = nullptr;
580   }
581 #endif
582 
583   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
584     if (__cntrl_)
585       __cntrl_->__add_shared();
586   }
587 
588   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
589   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
590     if (__cntrl_)
591       __cntrl_->__add_shared();
592   }
593 
594   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
595     __r.__ptr_   = nullptr;
596     __r.__cntrl_ = nullptr;
597   }
598 
599   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
600   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
601     __r.__ptr_   = nullptr;
602     __r.__cntrl_ = nullptr;
603   }
604 
605   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
606   _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(const weak_ptr<_Yp>& __r)
607       : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_ ? __r.__cntrl_->lock() : __r.__cntrl_) {
608     if (__cntrl_ == nullptr)
609       __throw_bad_weak_ptr();
610   }
611 
612 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
613   template <class _Yp, __enable_if_t<is_convertible<_Yp*, element_type*>::value, int> = 0>
614   _LIBCPP_HIDE_FROM_ABI shared_ptr(auto_ptr<_Yp>&& __r) : __ptr_(__r.get()) {
615     typedef __shared_ptr_pointer<_Yp*, default_delete<_Yp>, allocator<__remove_cv_t<_Yp> > > _CntrlBlk;
616     __cntrl_ = new _CntrlBlk(__r.get(), default_delete<_Yp>(), allocator<__remove_cv_t<_Yp> >());
617     __enable_weak_this(__r.get(), __r.get());
618     __r.release();
619   }
620 #endif
621 
622   template <class _Yp,
623             class _Dp,
624             __enable_if_t<!is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
625                               is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
626                           int> = 0>
627   _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
628 #if _LIBCPP_STD_VER >= 14
629     if (__ptr_ == nullptr)
630       __cntrl_ = nullptr;
631     else
632 #endif
633     {
634       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
635       typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer, _Dp, _AllocT> _CntrlBlk;
636       __cntrl_ = new _CntrlBlk(__r.get(), std::move(__r.get_deleter()), _AllocT());
637       __enable_weak_this(__r.get(), __r.get());
638     }
639     __r.release();
640   }
641 
642   template <class _Yp,
643             class _Dp,
644             class              = void,
645             __enable_if_t<is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
646                               is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
647                           int> = 0>
648   _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
649 #if _LIBCPP_STD_VER >= 14
650     if (__ptr_ == nullptr)
651       __cntrl_ = nullptr;
652     else
653 #endif
654     {
655       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
656       typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer,
657                                    reference_wrapper<__libcpp_remove_reference_t<_Dp> >,
658                                    _AllocT>
659           _CntrlBlk;
660       __cntrl_ = new _CntrlBlk(__r.get(), std::ref(__r.get_deleter()), _AllocT());
661       __enable_weak_this(__r.get(), __r.get());
662     }
663     __r.release();
664   }
665 
666   _LIBCPP_HIDE_FROM_ABI ~shared_ptr() {
667     if (__cntrl_)
668       __cntrl_->__release_shared();
669   }
670 
671   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr& __r) _NOEXCEPT {
672     shared_ptr(__r).swap(*this);
673     return *this;
674   }
675 
676   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
677   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr<_Yp>& __r) _NOEXCEPT {
678     shared_ptr(__r).swap(*this);
679     return *this;
680   }
681 
682   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr&& __r) _NOEXCEPT {
683     shared_ptr(std::move(__r)).swap(*this);
684     return *this;
685   }
686 
687   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
688   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr<_Yp>&& __r) {
689     shared_ptr(std::move(__r)).swap(*this);
690     return *this;
691   }
692 
693 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
694   template <class _Yp,
695             __enable_if_t<!is_array<_Yp>::value && is_convertible<_Yp*, typename shared_ptr<_Tp>::element_type*>::value,
696                           int> = 0>
697   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(auto_ptr<_Yp>&& __r) {
698     shared_ptr(std::move(__r)).swap(*this);
699     return *this;
700   }
701 #endif
702 
703   template <class _Yp,
704             class _Dp,
705             __enable_if_t<_And< __compatible_with<_Yp, _Tp>,
706                                 is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*> >::value,
707                           int> = 0>
708   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(unique_ptr<_Yp, _Dp>&& __r) {
709     shared_ptr(std::move(__r)).swap(*this);
710     return *this;
711   }
712 
713   _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr& __r) _NOEXCEPT {
714     std::swap(__ptr_, __r.__ptr_);
715     std::swap(__cntrl_, __r.__cntrl_);
716   }
717 
718   _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT { shared_ptr().swap(*this); }
719 
720   template <class _Yp, __enable_if_t<__raw_pointer_compatible_with<_Yp, _Tp>::value, int> = 0>
721   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p) {
722     shared_ptr(__p).swap(*this);
723   }
724 
725   template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
726   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d) {
727     shared_ptr(__p, __d).swap(*this);
728   }
729 
730   template <class _Yp,
731             class _Dp,
732             class _Alloc,
733             __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
734   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d, _Alloc __a) {
735     shared_ptr(__p, __d, __a).swap(*this);
736   }
737 
738   _LIBCPP_HIDE_FROM_ABI element_type* get() const _NOEXCEPT { return __ptr_; }
739 
740   _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator*() const _NOEXCEPT { return *__ptr_; }
741 
742   _LIBCPP_HIDE_FROM_ABI element_type* operator->() const _NOEXCEPT {
743     static_assert(!is_array<_Tp>::value, "std::shared_ptr<T>::operator-> is only valid when T is not an array type.");
744     return __ptr_;
745   }
746 
747   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __cntrl_ ? __cntrl_->use_count() : 0; }
748 
749 #if _LIBCPP_STD_VER < 20 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_SHARED_PTR_UNIQUE)
750   _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI bool unique() const _NOEXCEPT { return use_count() == 1; }
751 #endif
752 
753   _LIBCPP_HIDE_FROM_ABI explicit operator bool() const _NOEXCEPT { return get() != nullptr; }
754 
755   template <class _Up>
756   _LIBCPP_HIDE_FROM_ABI bool owner_before(shared_ptr<_Up> const& __p) const _NOEXCEPT {
757     return __cntrl_ < __p.__cntrl_;
758   }
759 
760   template <class _Up>
761   _LIBCPP_HIDE_FROM_ABI bool owner_before(weak_ptr<_Up> const& __p) const _NOEXCEPT {
762     return __cntrl_ < __p.__cntrl_;
763   }
764 
765   _LIBCPP_HIDE_FROM_ABI bool __owner_equivalent(const shared_ptr& __p) const { return __cntrl_ == __p.__cntrl_; }
766 
767 #if _LIBCPP_STD_VER >= 17
768   _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator[](ptrdiff_t __i) const {
769     static_assert(is_array<_Tp>::value, "std::shared_ptr<T>::operator[] is only valid when T is an array type.");
770     return __ptr_[__i];
771   }
772 #endif
773 
774 #ifndef _LIBCPP_HAS_NO_RTTI
775   template <class _Dp>
776   _LIBCPP_HIDE_FROM_ABI _Dp* __get_deleter() const _NOEXCEPT {
777     return static_cast<_Dp*>(__cntrl_ ? const_cast<void*>(__cntrl_->__get_deleter(typeid(_Dp))) : nullptr);
778   }
779 #endif // _LIBCPP_HAS_NO_RTTI
780 
781   template <class _Yp, class _CntrlBlk>
782   _LIBCPP_HIDE_FROM_ABI static shared_ptr<_Tp> __create_with_control_block(_Yp* __p, _CntrlBlk* __cntrl) _NOEXCEPT {
783     shared_ptr<_Tp> __r;
784     __r.__ptr_   = __p;
785     __r.__cntrl_ = __cntrl;
786     __r.__enable_weak_this(__r.__ptr_, __r.__ptr_);
787     return __r;
788   }
789 
790 private:
791   template <class _Yp, bool = is_function<_Yp>::value>
792   struct __shared_ptr_default_allocator {
793     typedef allocator<__remove_cv_t<_Yp> > type;
794   };
795 
796   template <class _Yp>
797   struct __shared_ptr_default_allocator<_Yp, true> {
798     typedef allocator<__shared_ptr_dummy_rebind_allocator_type> type;
799   };
800 
801   template <class _Yp,
802             class _OrigPtr,
803             __enable_if_t<is_convertible<_OrigPtr*, const enable_shared_from_this<_Yp>*>::value, int> = 0>
804   _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(const enable_shared_from_this<_Yp>* __e, _OrigPtr* __ptr) _NOEXCEPT {
805     typedef __remove_cv_t<_Yp> _RawYp;
806     if (__e && __e->__weak_this_.expired()) {
807       __e->__weak_this_ = shared_ptr<_RawYp>(*this, const_cast<_RawYp*>(static_cast<const _Yp*>(__ptr)));
808     }
809   }
810 
811   _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(...) _NOEXCEPT {}
812 
813   template <class, class _Yp>
814   struct __shared_ptr_default_delete : default_delete<_Yp> {};
815 
816   template <class _Yp, class _Un, size_t _Sz>
817   struct __shared_ptr_default_delete<_Yp[_Sz], _Un> : default_delete<_Yp[]> {};
818 
819   template <class _Yp, class _Un>
820   struct __shared_ptr_default_delete<_Yp[], _Un> : default_delete<_Yp[]> {};
821 
822   template <class _Up>
823   friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
824   template <class _Up>
825   friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
826 };
827 
828 #if _LIBCPP_STD_VER >= 17
829 template <class _Tp>
830 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
831 template <class _Tp, class _Dp>
832 shared_ptr(unique_ptr<_Tp, _Dp>) -> shared_ptr<_Tp>;
833 #endif
834 
835 //
836 // std::allocate_shared and std::make_shared
837 //
838 template <class _Tp, class _Alloc, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
839 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, _Args&&... __args) {
840   using _ControlBlock          = __shared_ptr_emplace<_Tp, _Alloc>;
841   using _ControlBlockAllocator = typename __allocator_traits_rebind<_Alloc, _ControlBlock>::type;
842   __allocation_guard<_ControlBlockAllocator> __guard(__a, 1);
843   ::new ((void*)std::addressof(*__guard.__get())) _ControlBlock(__a, std::forward<_Args>(__args)...);
844   auto __control_block = __guard.__release_ptr();
845   return shared_ptr<_Tp>::__create_with_control_block(
846       (*__control_block).__get_elem(), std::addressof(*__control_block));
847 }
848 
849 template <class _Tp, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
850 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(_Args&&... __args) {
851   return std::allocate_shared<_Tp>(allocator<__remove_cv_t<_Tp> >(), std::forward<_Args>(__args)...);
852 }
853 
854 #if _LIBCPP_STD_VER >= 20
855 
856 template <class _Tp, class _Alloc, __enable_if_t<!is_array<_Tp>::value, int> = 0>
857 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
858   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
859   _ForOverwriteAllocator __alloc(__a);
860   return std::allocate_shared<_Tp>(__alloc);
861 }
862 
863 template <class _Tp, __enable_if_t<!is_array<_Tp>::value, int> = 0>
864 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
865   return std::allocate_shared_for_overwrite<_Tp>(allocator<__remove_cv_t<_Tp>>());
866 }
867 
868 #endif // _LIBCPP_STD_VER >= 20
869 
870 #if _LIBCPP_STD_VER >= 17
871 
872 template <size_t _Alignment>
873 struct __sp_aligned_storage {
874   alignas(_Alignment) char __storage[_Alignment];
875 };
876 
877 template <class _Tp, class _Alloc>
878 struct __unbounded_array_control_block;
879 
880 template <class _Tp, class _Alloc>
881 struct __unbounded_array_control_block<_Tp[], _Alloc> : __shared_weak_count {
882   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }
883 
884   _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(
885       _Alloc const& __alloc, size_t __count, _Tp const& __arg)
886       : __alloc_(__alloc), __count_(__count) {
887     std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::begin(__data_), __count_, __arg);
888   }
889 
890   _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(_Alloc const& __alloc, size_t __count)
891       : __alloc_(__alloc), __count_(__count) {
892 #  if _LIBCPP_STD_VER >= 20
893     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
894       // We are purposefully not using an allocator-aware default construction because the spec says so.
895       // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
896       std::uninitialized_default_construct_n(std::begin(__data_), __count_);
897     } else {
898       std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
899     }
900 #  else
901     std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
902 #  endif
903   }
904 
905   // Returns the number of bytes required to store a control block followed by the given number
906   // of elements of _Tp, with the whole storage being aligned to a multiple of _Tp's alignment.
907   _LIBCPP_HIDE_FROM_ABI static constexpr size_t __bytes_for(size_t __elements) {
908     // When there's 0 elements, the control block alone is enough since it holds one element.
909     // Otherwise, we allocate one fewer element than requested because the control block already
910     // holds one. Also, we use the bitwise formula below to ensure that we allocate enough bytes
911     // for the whole allocation to be a multiple of _Tp's alignment. That formula is taken from [1].
912     //
913     // [1]: https://en.wikipedia.org/wiki/Data_structure_alignment#Computing_padding
914     size_t __bytes           = __elements == 0 ? sizeof(__unbounded_array_control_block)
915                                                : (__elements - 1) * sizeof(_Tp) + sizeof(__unbounded_array_control_block);
916     constexpr size_t __align = alignof(_Tp);
917     return (__bytes + __align - 1) & ~(__align - 1);
918   }
919 
920   _LIBCPP_HIDE_FROM_ABI_VIRTUAL
921   ~__unbounded_array_control_block() override {
922   } // can't be `= default` because of the sometimes-non-trivial union member __data_
923 
924 private:
925   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
926 #  if _LIBCPP_STD_VER >= 20
927     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
928       std::__reverse_destroy(__data_, __data_ + __count_);
929     } else {
930       __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
931       std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
932     }
933 #  else
934     __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
935     std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
936 #  endif
937   }
938 
939   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
940     using _AlignedStorage = __sp_aligned_storage<alignof(__unbounded_array_control_block)>;
941     using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
942     using _PointerTraits  = pointer_traits<typename allocator_traits<_StorageAlloc>::pointer>;
943 
944     _StorageAlloc __tmp(__alloc_);
945     __alloc_.~_Alloc();
946     size_t __size              = __unbounded_array_control_block::__bytes_for(__count_);
947     _AlignedStorage* __storage = reinterpret_cast<_AlignedStorage*>(this);
948     allocator_traits<_StorageAlloc>::deallocate(
949         __tmp, _PointerTraits::pointer_to(*__storage), __size / sizeof(_AlignedStorage));
950   }
951 
952   _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
953   size_t __count_;
954   union {
955     _Tp __data_[1];
956   };
957 };
958 
959 template <class _Array, class _Alloc, class... _Arg>
960 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Array>
961 __allocate_shared_unbounded_array(const _Alloc& __a, size_t __n, _Arg&&... __arg) {
962   static_assert(__libcpp_is_unbounded_array<_Array>::value);
963   // We compute the number of bytes necessary to hold the control block and the
964   // array elements. Then, we allocate an array of properly-aligned dummy structs
965   // large enough to hold the control block and array. This allows shifting the
966   // burden of aligning memory properly from us to the allocator.
967   using _ControlBlock   = __unbounded_array_control_block<_Array, _Alloc>;
968   using _AlignedStorage = __sp_aligned_storage<alignof(_ControlBlock)>;
969   using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
970   __allocation_guard<_StorageAlloc> __guard(__a, _ControlBlock::__bytes_for(__n) / sizeof(_AlignedStorage));
971   _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
972   std::__construct_at(__control_block, __a, __n, std::forward<_Arg>(__arg)...);
973   __guard.__release_ptr();
974   return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
975 }
976 
977 template <class _Tp, class _Alloc>
978 struct __bounded_array_control_block;
979 
980 template <class _Tp, size_t _Count, class _Alloc>
981 struct __bounded_array_control_block<_Tp[_Count], _Alloc> : __shared_weak_count {
982   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }
983 
984   _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc, _Tp const& __arg)
985       : __alloc_(__alloc) {
986     std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count, __arg);
987   }
988 
989   _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc) : __alloc_(__alloc) {
990 #  if _LIBCPP_STD_VER >= 20
991     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
992       // We are purposefully not using an allocator-aware default construction because the spec says so.
993       // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
994       std::uninitialized_default_construct_n(std::addressof(__data_[0]), _Count);
995     } else {
996       std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
997     }
998 #  else
999     std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
1000 #  endif
1001   }
1002 
1003   _LIBCPP_HIDE_FROM_ABI_VIRTUAL
1004   ~__bounded_array_control_block() override {
1005   } // can't be `= default` because of the sometimes-non-trivial union member __data_
1006 
1007 private:
1008   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
1009 #  if _LIBCPP_STD_VER >= 20
1010     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
1011       std::__reverse_destroy(__data_, __data_ + _Count);
1012     } else {
1013       __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
1014       std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
1015     }
1016 #  else
1017     __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
1018     std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
1019 #  endif
1020   }
1021 
1022   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
1023     using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, __bounded_array_control_block>;
1024     using _PointerTraits     = pointer_traits<typename allocator_traits<_ControlBlockAlloc>::pointer>;
1025 
1026     _ControlBlockAlloc __tmp(__alloc_);
1027     __alloc_.~_Alloc();
1028     allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, _PointerTraits::pointer_to(*this), 1);
1029   }
1030 
1031   _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
1032   union {
1033     _Tp __data_[_Count];
1034   };
1035 };
1036 
1037 template <class _Array, class _Alloc, class... _Arg>
1038 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Array> __allocate_shared_bounded_array(const _Alloc& __a, _Arg&&... __arg) {
1039   static_assert(__libcpp_is_bounded_array<_Array>::value);
1040   using _ControlBlock      = __bounded_array_control_block<_Array, _Alloc>;
1041   using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, _ControlBlock>;
1042 
1043   __allocation_guard<_ControlBlockAlloc> __guard(__a, 1);
1044   _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
1045   std::__construct_at(__control_block, __a, std::forward<_Arg>(__arg)...);
1046   __guard.__release_ptr();
1047   return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
1048 }
1049 
1050 #endif // _LIBCPP_STD_VER >= 17
1051 
1052 #if _LIBCPP_STD_VER >= 20
1053 
1054 // bounded array variants
1055 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1056 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a) {
1057   return std::__allocate_shared_bounded_array<_Tp>(__a);
1058 }
1059 
1060 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1061 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, const remove_extent_t<_Tp>& __u) {
1062   return std::__allocate_shared_bounded_array<_Tp>(__a, __u);
1063 }
1064 
1065 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1066 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
1067   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
1068   _ForOverwriteAllocator __alloc(__a);
1069   return std::__allocate_shared_bounded_array<_Tp>(__alloc);
1070 }
1071 
1072 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1073 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared() {
1074   return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>());
1075 }
1076 
1077 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1078 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(const remove_extent_t<_Tp>& __u) {
1079   return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>(), __u);
1080 }
1081 
1082 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1083 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
1084   return std::__allocate_shared_bounded_array<_Tp>(allocator<__for_overwrite_tag>());
1085 }
1086 
1087 // unbounded array variants
1088 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1089 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n) {
1090   return std::__allocate_shared_unbounded_array<_Tp>(__a, __n);
1091 }
1092 
1093 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1094 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n, const remove_extent_t<_Tp>& __u) {
1095   return std::__allocate_shared_unbounded_array<_Tp>(__a, __n, __u);
1096 }
1097 
1098 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1099 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a, size_t __n) {
1100   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
1101   _ForOverwriteAllocator __alloc(__a);
1102   return std::__allocate_shared_unbounded_array<_Tp>(__alloc, __n);
1103 }
1104 
1105 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1106 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n) {
1107   return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n);
1108 }
1109 
1110 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1111 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n, const remove_extent_t<_Tp>& __u) {
1112   return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n, __u);
1113 }
1114 
1115 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1116 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite(size_t __n) {
1117   return std::__allocate_shared_unbounded_array<_Tp>(allocator<__for_overwrite_tag>(), __n);
1118 }
1119 
1120 #endif // _LIBCPP_STD_VER >= 20
1121 
1122 template <class _Tp, class _Up>
1123 inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1124   return __x.get() == __y.get();
1125 }
1126 
1127 #if _LIBCPP_STD_VER <= 17
1128 
1129 template <class _Tp, class _Up>
1130 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1131   return !(__x == __y);
1132 }
1133 
1134 template <class _Tp, class _Up>
1135 inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1136 #  if _LIBCPP_STD_VER <= 11
1137   typedef typename common_type<_Tp*, _Up*>::type _Vp;
1138   return less<_Vp>()(__x.get(), __y.get());
1139 #  else
1140   return less<>()(__x.get(), __y.get());
1141 #  endif
1142 }
1143 
1144 template <class _Tp, class _Up>
1145 inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1146   return __y < __x;
1147 }
1148 
1149 template <class _Tp, class _Up>
1150 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1151   return !(__y < __x);
1152 }
1153 
1154 template <class _Tp, class _Up>
1155 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1156   return !(__x < __y);
1157 }
1158 
1159 #endif // _LIBCPP_STD_VER <= 17
1160 
1161 #if _LIBCPP_STD_VER >= 20
1162 template <class _Tp, class _Up>
1163 _LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) noexcept {
1164   return compare_three_way()(__x.get(), __y.get());
1165 }
1166 #endif
1167 
1168 template <class _Tp>
1169 inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1170   return !__x;
1171 }
1172 
1173 #if _LIBCPP_STD_VER <= 17
1174 
1175 template <class _Tp>
1176 inline _LIBCPP_HIDE_FROM_ABI bool operator==(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1177   return !__x;
1178 }
1179 
1180 template <class _Tp>
1181 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1182   return static_cast<bool>(__x);
1183 }
1184 
1185 template <class _Tp>
1186 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1187   return static_cast<bool>(__x);
1188 }
1189 
1190 template <class _Tp>
1191 inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1192   return less<typename shared_ptr<_Tp>::element_type*>()(__x.get(), nullptr);
1193 }
1194 
1195 template <class _Tp>
1196 inline _LIBCPP_HIDE_FROM_ABI bool operator<(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1197   return less<typename shared_ptr<_Tp>::element_type*>()(nullptr, __x.get());
1198 }
1199 
1200 template <class _Tp>
1201 inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1202   return nullptr < __x;
1203 }
1204 
1205 template <class _Tp>
1206 inline _LIBCPP_HIDE_FROM_ABI bool operator>(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1207   return __x < nullptr;
1208 }
1209 
1210 template <class _Tp>
1211 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1212   return !(nullptr < __x);
1213 }
1214 
1215 template <class _Tp>
1216 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1217   return !(__x < nullptr);
1218 }
1219 
1220 template <class _Tp>
1221 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1222   return !(__x < nullptr);
1223 }
1224 
1225 template <class _Tp>
1226 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1227   return !(nullptr < __x);
1228 }
1229 
1230 #endif // _LIBCPP_STD_VER <= 17
1231 
1232 #if _LIBCPP_STD_VER >= 20
1233 template <class _Tp>
1234 _LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, nullptr_t) noexcept {
1235   return compare_three_way()(__x.get(), static_cast<typename shared_ptr<_Tp>::element_type*>(nullptr));
1236 }
1237 #endif
1238 
1239 template <class _Tp>
1240 inline _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr<_Tp>& __x, shared_ptr<_Tp>& __y) _NOEXCEPT {
1241   __x.swap(__y);
1242 }
1243 
1244 template <class _Tp, class _Up>
1245 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1246   return shared_ptr<_Tp>(__r, static_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
1247 }
1248 
1249 // LWG-2996
1250 // We don't backport because it is an evolutionary change.
1251 #if _LIBCPP_STD_VER >= 20
1252 template <class _Tp, class _Up>
1253 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1254   return shared_ptr<_Tp>(std::move(__r), static_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1255 }
1256 #endif
1257 
1258 template <class _Tp, class _Up>
1259 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1260   typedef typename shared_ptr<_Tp>::element_type _ET;
1261   _ET* __p = dynamic_cast<_ET*>(__r.get());
1262   return __p ? shared_ptr<_Tp>(__r, __p) : shared_ptr<_Tp>();
1263 }
1264 
1265 // LWG-2996
1266 // We don't backport because it is an evolutionary change.
1267 #if _LIBCPP_STD_VER >= 20
1268 template <class _Tp, class _Up>
1269 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1270   auto* __p = dynamic_cast<typename shared_ptr<_Tp>::element_type*>(__r.get());
1271   return __p ? shared_ptr<_Tp>(std::move(__r), __p) : shared_ptr<_Tp>();
1272 }
1273 #endif
1274 
1275 template <class _Tp, class _Up>
1276 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1277   typedef typename shared_ptr<_Tp>::element_type _RTp;
1278   return shared_ptr<_Tp>(__r, const_cast<_RTp*>(__r.get()));
1279 }
1280 
1281 // LWG-2996
1282 // We don't backport because it is an evolutionary change.
1283 #if _LIBCPP_STD_VER >= 20
1284 template <class _Tp, class _Up>
1285 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1286   return shared_ptr<_Tp>(std::move(__r), const_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1287 }
1288 #endif
1289 
1290 template <class _Tp, class _Up>
1291 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1292   return shared_ptr<_Tp>(__r, reinterpret_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
1293 }
1294 
1295 // LWG-2996
1296 // We don't backport because it is an evolutionary change.
1297 #if _LIBCPP_STD_VER >= 20
1298 template <class _Tp, class _Up>
1299 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1300   return shared_ptr<_Tp>(std::move(__r), reinterpret_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1301 }
1302 #endif
1303 
1304 #ifndef _LIBCPP_HAS_NO_RTTI
1305 
1306 template <class _Dp, class _Tp>
1307 inline _LIBCPP_HIDE_FROM_ABI _Dp* get_deleter(const shared_ptr<_Tp>& __p) _NOEXCEPT {
1308   return __p.template __get_deleter<_Dp>();
1309 }
1310 
1311 #endif // _LIBCPP_HAS_NO_RTTI
1312 
1313 template <class _Tp>
1314 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS weak_ptr {
1315 public:
1316 #if _LIBCPP_STD_VER >= 17
1317   typedef remove_extent_t<_Tp> element_type;
1318 #else
1319   typedef _Tp element_type;
1320 #endif
1321 
1322   // A weak_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
1323   // any bookkeeping, so it's always trivially relocatable.
1324   using __trivially_relocatable = weak_ptr;
1325 
1326 private:
1327   element_type* __ptr_;
1328   __shared_weak_count* __cntrl_;
1329 
1330 public:
1331   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR weak_ptr() _NOEXCEPT;
1332 
1333   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1334   _LIBCPP_HIDE_FROM_ABI weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT;
1335 
1336   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr const& __r) _NOEXCEPT;
1337 
1338   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1339   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT;
1340 
1341   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr&& __r) _NOEXCEPT;
1342 
1343   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1344   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT;
1345 
1346   _LIBCPP_HIDE_FROM_ABI ~weak_ptr();
1347 
1348   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr const& __r) _NOEXCEPT;
1349   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1350   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT;
1351 
1352   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr&& __r) _NOEXCEPT;
1353   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1354   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT;
1355 
1356   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1357   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT;
1358 
1359   _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr& __r) _NOEXCEPT;
1360   _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT;
1361 
1362   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __cntrl_ ? __cntrl_->use_count() : 0; }
1363   _LIBCPP_HIDE_FROM_ABI bool expired() const _NOEXCEPT { return __cntrl_ == nullptr || __cntrl_->use_count() == 0; }
1364   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> lock() const _NOEXCEPT;
1365   template <class _Up>
1366   _LIBCPP_HIDE_FROM_ABI bool owner_before(const shared_ptr<_Up>& __r) const _NOEXCEPT {
1367     return __cntrl_ < __r.__cntrl_;
1368   }
1369   template <class _Up>
1370   _LIBCPP_HIDE_FROM_ABI bool owner_before(const weak_ptr<_Up>& __r) const _NOEXCEPT {
1371     return __cntrl_ < __r.__cntrl_;
1372   }
1373 
1374   template <class _Up>
1375   friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
1376   template <class _Up>
1377   friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
1378 };
1379 
1380 #if _LIBCPP_STD_VER >= 17
1381 template <class _Tp>
1382 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
1383 #endif
1384 
1385 template <class _Tp>
1386 inline _LIBCPP_CONSTEXPR weak_ptr<_Tp>::weak_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
1387 
1388 template <class _Tp>
1389 inline weak_ptr<_Tp>::weak_ptr(weak_ptr const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
1390   if (__cntrl_)
1391     __cntrl_->__add_weak();
1392 }
1393 
1394 template <class _Tp>
1395 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1396 inline weak_ptr<_Tp>::weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
1397   if (__cntrl_)
1398     __cntrl_->__add_weak();
1399 }
1400 
1401 template <class _Tp>
1402 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1403 inline weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
1404   shared_ptr<_Yp> __s = __r.lock();
1405   *this               = weak_ptr<_Tp>(__s);
1406 }
1407 
1408 template <class _Tp>
1409 inline weak_ptr<_Tp>::weak_ptr(weak_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
1410   __r.__ptr_   = nullptr;
1411   __r.__cntrl_ = nullptr;
1412 }
1413 
1414 template <class _Tp>
1415 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1416 inline weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
1417   shared_ptr<_Yp> __s = __r.lock();
1418   *this               = weak_ptr<_Tp>(__s);
1419   __r.reset();
1420 }
1421 
1422 template <class _Tp>
1423 weak_ptr<_Tp>::~weak_ptr() {
1424   if (__cntrl_)
1425     __cntrl_->__release_weak();
1426 }
1427 
1428 template <class _Tp>
1429 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr const& __r) _NOEXCEPT {
1430   weak_ptr(__r).swap(*this);
1431   return *this;
1432 }
1433 
1434 template <class _Tp>
1435 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1436 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT {
1437   weak_ptr(__r).swap(*this);
1438   return *this;
1439 }
1440 
1441 template <class _Tp>
1442 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr&& __r) _NOEXCEPT {
1443   weak_ptr(std::move(__r)).swap(*this);
1444   return *this;
1445 }
1446 
1447 template <class _Tp>
1448 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1449 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT {
1450   weak_ptr(std::move(__r)).swap(*this);
1451   return *this;
1452 }
1453 
1454 template <class _Tp>
1455 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1456 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT {
1457   weak_ptr(__r).swap(*this);
1458   return *this;
1459 }
1460 
1461 template <class _Tp>
1462 inline void weak_ptr<_Tp>::swap(weak_ptr& __r) _NOEXCEPT {
1463   std::swap(__ptr_, __r.__ptr_);
1464   std::swap(__cntrl_, __r.__cntrl_);
1465 }
1466 
1467 template <class _Tp>
1468 inline _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr<_Tp>& __x, weak_ptr<_Tp>& __y) _NOEXCEPT {
1469   __x.swap(__y);
1470 }
1471 
1472 template <class _Tp>
1473 inline void weak_ptr<_Tp>::reset() _NOEXCEPT {
1474   weak_ptr().swap(*this);
1475 }
1476 
1477 template <class _Tp>
1478 shared_ptr<_Tp> weak_ptr<_Tp>::lock() const _NOEXCEPT {
1479   shared_ptr<_Tp> __r;
1480   __r.__cntrl_ = __cntrl_ ? __cntrl_->lock() : __cntrl_;
1481   if (__r.__cntrl_)
1482     __r.__ptr_ = __ptr_;
1483   return __r;
1484 }
1485 
1486 #if _LIBCPP_STD_VER >= 17
1487 template <class _Tp = void>
1488 struct owner_less;
1489 #else
1490 template <class _Tp>
1491 struct owner_less;
1492 #endif
1493 
1494 template <class _Tp>
1495 struct _LIBCPP_TEMPLATE_VIS owner_less<shared_ptr<_Tp> > : __binary_function<shared_ptr<_Tp>, shared_ptr<_Tp>, bool> {
1496   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
1497     return __x.owner_before(__y);
1498   }
1499   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
1500     return __x.owner_before(__y);
1501   }
1502   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
1503     return __x.owner_before(__y);
1504   }
1505 };
1506 
1507 template <class _Tp>
1508 struct _LIBCPP_TEMPLATE_VIS owner_less<weak_ptr<_Tp> > : __binary_function<weak_ptr<_Tp>, weak_ptr<_Tp>, bool> {
1509   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
1510     return __x.owner_before(__y);
1511   }
1512   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
1513     return __x.owner_before(__y);
1514   }
1515   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
1516     return __x.owner_before(__y);
1517   }
1518 };
1519 
1520 #if _LIBCPP_STD_VER >= 17
1521 template <>
1522 struct _LIBCPP_TEMPLATE_VIS owner_less<void> {
1523   template <class _Tp, class _Up>
1524   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
1525     return __x.owner_before(__y);
1526   }
1527   template <class _Tp, class _Up>
1528   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
1529     return __x.owner_before(__y);
1530   }
1531   template <class _Tp, class _Up>
1532   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
1533     return __x.owner_before(__y);
1534   }
1535   template <class _Tp, class _Up>
1536   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
1537     return __x.owner_before(__y);
1538   }
1539   typedef void is_transparent;
1540 };
1541 #endif
1542 
1543 template <class _Tp>
1544 class _LIBCPP_TEMPLATE_VIS enable_shared_from_this {
1545   mutable weak_ptr<_Tp> __weak_this_;
1546 
1547 protected:
1548   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR enable_shared_from_this() _NOEXCEPT {}
1549   _LIBCPP_HIDE_FROM_ABI enable_shared_from_this(enable_shared_from_this const&) _NOEXCEPT {}
1550   _LIBCPP_HIDE_FROM_ABI enable_shared_from_this& operator=(enable_shared_from_this const&) _NOEXCEPT { return *this; }
1551   _LIBCPP_HIDE_FROM_ABI ~enable_shared_from_this() {}
1552 
1553 public:
1554   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> shared_from_this() { return shared_ptr<_Tp>(__weak_this_); }
1555   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp const> shared_from_this() const { return shared_ptr<const _Tp>(__weak_this_); }
1556 
1557 #if _LIBCPP_STD_VER >= 17
1558   _LIBCPP_HIDE_FROM_ABI weak_ptr<_Tp> weak_from_this() _NOEXCEPT { return __weak_this_; }
1559 
1560   _LIBCPP_HIDE_FROM_ABI weak_ptr<const _Tp> weak_from_this() const _NOEXCEPT { return __weak_this_; }
1561 #endif // _LIBCPP_STD_VER >= 17
1562 
1563   template <class _Up>
1564   friend class shared_ptr;
1565 };
1566 
1567 template <class _Tp>
1568 struct _LIBCPP_TEMPLATE_VIS hash;
1569 
1570 template <class _Tp>
1571 struct _LIBCPP_TEMPLATE_VIS hash<shared_ptr<_Tp> > {
1572 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_BINDER_TYPEDEFS)
1573   _LIBCPP_DEPRECATED_IN_CXX17 typedef shared_ptr<_Tp> argument_type;
1574   _LIBCPP_DEPRECATED_IN_CXX17 typedef size_t result_type;
1575 #endif
1576 
1577   _LIBCPP_HIDE_FROM_ABI size_t operator()(const shared_ptr<_Tp>& __ptr) const _NOEXCEPT {
1578     return hash<typename shared_ptr<_Tp>::element_type*>()(__ptr.get());
1579   }
1580 };
1581 
1582 template <class _CharT, class _Traits, class _Yp>
1583 inline _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
1584 operator<<(basic_ostream<_CharT, _Traits>& __os, shared_ptr<_Yp> const& __p);
1585 
1586 #if !defined(_LIBCPP_HAS_NO_THREADS)
1587 
1588 class _LIBCPP_EXPORTED_FROM_ABI __sp_mut {
1589   void* __lx_;
1590 
1591 public:
1592   void lock() _NOEXCEPT;
1593   void unlock() _NOEXCEPT;
1594 
1595 private:
1596   _LIBCPP_CONSTEXPR __sp_mut(void*) _NOEXCEPT;
1597   __sp_mut(const __sp_mut&);
1598   __sp_mut& operator=(const __sp_mut&);
1599 
1600   friend _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
1601 };
1602 
1603 _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
1604 
1605 template <class _Tp>
1606 inline _LIBCPP_HIDE_FROM_ABI bool atomic_is_lock_free(const shared_ptr<_Tp>*) {
1607   return false;
1608 }
1609 
1610 template <class _Tp>
1611 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load(const shared_ptr<_Tp>* __p) {
1612   __sp_mut& __m = std::__get_sp_mut(__p);
1613   __m.lock();
1614   shared_ptr<_Tp> __q = *__p;
1615   __m.unlock();
1616   return __q;
1617 }
1618 
1619 template <class _Tp>
1620 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order) {
1621   return std::atomic_load(__p);
1622 }
1623 
1624 template <class _Tp>
1625 _LIBCPP_HIDE_FROM_ABI void atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
1626   __sp_mut& __m = std::__get_sp_mut(__p);
1627   __m.lock();
1628   __p->swap(__r);
1629   __m.unlock();
1630 }
1631 
1632 template <class _Tp>
1633 inline _LIBCPP_HIDE_FROM_ABI void atomic_store_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
1634   std::atomic_store(__p, __r);
1635 }
1636 
1637 template <class _Tp>
1638 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
1639   __sp_mut& __m = std::__get_sp_mut(__p);
1640   __m.lock();
1641   __p->swap(__r);
1642   __m.unlock();
1643   return __r;
1644 }
1645 
1646 template <class _Tp>
1647 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
1648 atomic_exchange_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
1649   return std::atomic_exchange(__p, __r);
1650 }
1651 
1652 template <class _Tp>
1653 _LIBCPP_HIDE_FROM_ABI bool
1654 atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
1655   shared_ptr<_Tp> __temp;
1656   __sp_mut& __m = std::__get_sp_mut(__p);
1657   __m.lock();
1658   if (__p->__owner_equivalent(*__v)) {
1659     std::swap(__temp, *__p);
1660     *__p = __w;
1661     __m.unlock();
1662     return true;
1663   }
1664   std::swap(__temp, *__v);
1665   *__v = *__p;
1666   __m.unlock();
1667   return false;
1668 }
1669 
1670 template <class _Tp>
1671 inline _LIBCPP_HIDE_FROM_ABI bool
1672 atomic_compare_exchange_weak(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
1673   return std::atomic_compare_exchange_strong(__p, __v, __w);
1674 }
1675 
1676 template <class _Tp>
1677 inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_strong_explicit(
1678     shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
1679   return std::atomic_compare_exchange_strong(__p, __v, __w);
1680 }
1681 
1682 template <class _Tp>
1683 inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_weak_explicit(
1684     shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
1685   return std::atomic_compare_exchange_weak(__p, __v, __w);
1686 }
1687 
1688 #endif // !defined(_LIBCPP_HAS_NO_THREADS)
1689 
1690 _LIBCPP_END_NAMESPACE_STD
1691 
1692 _LIBCPP_POP_MACROS
1693 
1694 #endif // _LIBCPP___MEMORY_SHARED_PTR_H
1695