shared_ptr.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___MEMORY_SHARED_PTR_H
#define _LIBCPP___MEMORY_SHARED_PTR_H

#include <__atomic/memory_order.h>
#include <__compare/compare_three_way.h>
#include <__compare/ordering.h>
#include <__config>
#include <__cstddef/nullptr_t.h>
#include <__cstddef/ptrdiff_t.h>
#include <__exception/exception.h>
#include <__functional/binary_function.h>
#include <__functional/operations.h>
#include <__functional/reference_wrapper.h>
#include <__fwd/ostream.h>
#include <__iterator/access.h>
#include <__memory/addressof.h>
#include <__memory/allocation_guard.h>
#include <__memory/allocator.h>
#include <__memory/allocator_destructor.h>
#include <__memory/allocator_traits.h>
#include <__memory/auto_ptr.h>
#include <__memory/construct_at.h>
#include <__memory/destroy.h>
#include <__memory/pointer_traits.h>
#include <__memory/shared_count.h>
#include <__memory/uninitialized_algorithms.h>
#include <__memory/uninitialized_multidimensional_algorithms.h>
#include <__memory/unique_ptr.h>
#include <__type_traits/add_reference.h>
#include <__type_traits/conditional.h>
#include <__type_traits/conjunction.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/is_array.h>
#include <__type_traits/is_constructible.h>
#include <__type_traits/is_convertible.h>
#include <__type_traits/is_function.h>
#include <__type_traits/is_reference.h>
#include <__type_traits/is_same.h>
#include <__type_traits/nat.h>
#include <__type_traits/remove_cv.h>
#include <__type_traits/remove_extent.h>
#include <__type_traits/remove_pointer.h>
#include <__type_traits/remove_reference.h>
#include <__type_traits/void_t.h>
#include <__utility/declval.h>
#include <__utility/exception_guard.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <__utility/swap.h>
#include <__verbose_abort>
#include <typeinfo>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD
_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS

class _LIBCPP_EXPORTED_FROM_ABI bad_weak_ptr : public std::exception {
public:
  _LIBCPP_HIDE_FROM_ABI bad_weak_ptr() _NOEXCEPT                               = default;
  _LIBCPP_HIDE_FROM_ABI bad_weak_ptr(const bad_weak_ptr&) _NOEXCEPT            = default;
  _LIBCPP_HIDE_FROM_ABI bad_weak_ptr& operator=(const bad_weak_ptr&) _NOEXCEPT = default;
  ~bad_weak_ptr() _NOEXCEPT override;
  [[__nodiscard__]] const char* what() const _NOEXCEPT override;
};

[[__noreturn__]] inline _LIBCPP_HIDE_FROM_ABI void __throw_bad_weak_ptr() {
#if _LIBCPP_HAS_EXCEPTIONS
  throw bad_weak_ptr();
#else
  _LIBCPP_VERBOSE_ABORT("bad_weak_ptr was thrown in -fno-exceptions mode");
#endif
}

template <class _Tp>
class weak_ptr;

template <class _Tp, class _Dp, class _Alloc>
class _LIBCPP_HIDE_STRUCT_FROM_ABI __shared_ptr_pointer final : public __shared_weak_count {
  _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
  _LIBCPP_NO_UNIQUE_ADDRESS _Dp __deleter_;
  _LIBCPP_NO_UNIQUE_ADDRESS _Tp __ptr_;

public:
  _LIBCPP_HIDE_FROM_ABI __shared_ptr_pointer(_Tp __p, _Dp __d, _Alloc __a)
      : __alloc_(std::move(__a)), __deleter_(std::move(__d)), __ptr_(__p) {}

#if _LIBCPP_HAS_RTTI
  _LIBCPP_HIDE_FROM_ABI_VIRTUAL const void* __get_deleter(const type_info& __t) const _NOEXCEPT override {
    return __t == typeid(_Dp) ? std::addressof(__deleter_) : nullptr;
  }
#endif

private:
  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
    __deleter_(__ptr_);
    __ptr_.~_Tp();
    __deleter_.~_Dp();
  }

  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
    using __alloc_t = __allocator_traits_rebind_t<_Alloc, __shared_ptr_pointer>;

    __alloc_t __a(__alloc_);
    __alloc_.~_Alloc();
    __a.deallocate(pointer_traits<typename allocator_traits<__alloc_t>::pointer>::pointer_to(*this), 1);
  }
};

// This tag is used to instantiate an allocator type. The various shared_ptr control blocks
// detect that the allocator has been instantiated for this type and perform alternative
// initialization/destruction based on that.
struct __for_overwrite_tag {};

template <class _Tp, class _Alloc>
struct _LIBCPP_HIDE_STRUCT_FROM_ABI __shared_ptr_emplace : __shared_weak_count {
  using __alloc_traits _LIBCPP_NODEBUG = allocator_traits<_Alloc>;
  using __value_type _LIBCPP_NODEBUG   = __remove_cv_t<_Tp>;

  template <class... _Args>
  _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&... __args) : __alloc_(std::move(__a)) {
    allocator_traits<_Alloc>::construct(__alloc_, __get_elem(), std::forward<_Args>(__args)...);
  }

  _LIBCPP_HIDE_FROM_ABI __value_type* __get_elem() _NOEXCEPT { return reinterpret_cast<__value_type*>(__buffer_); }

private:
  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
    allocator_traits<_Alloc>::destroy(__alloc_, __get_elem());
  }

  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
    using __alloc_t = __allocator_traits_rebind_t<_Alloc, __shared_ptr_emplace>;
    __alloc_t __tmp(__alloc_);
    __alloc_.~_Alloc();
    allocator_traits<__alloc_t>::deallocate(
        __tmp, pointer_traits<typename allocator_traits<__alloc_t>::pointer>::pointer_to(*this), 1);
  }

  _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
  _ALIGNAS_TYPE(__value_type) char __buffer_[sizeof(__value_type)];
};

template <class _Tp, class _Alloc>
struct _LIBCPP_HIDE_STRUCT_FROM_ABI __shared_ptr_emplace_for_overwrite : __shared_weak_count {
  using __value_type _LIBCPP_NODEBUG = __remove_cv_t<_Tp>;

  _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace_for_overwrite(_Alloc __a) : __alloc_(std::move(__a)) {}

  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override { __value_.~__value_type(); }
  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
    using __alloc_t      = __allocator_traits_rebind_t<_Alloc, __shared_ptr_emplace_for_overwrite>;
    using __alloc_traits = allocator_traits<__alloc_t>;
    __alloc_t __tmp(__alloc_);
    __alloc_.~_Alloc();
    __alloc_traits::deallocate(__tmp, pointer_traits<typename __alloc_traits::pointer>::pointer_to(*this), 1);
  }

  _LIBCPP_HIDE_FROM_ABI __value_type* __get_elem() _NOEXCEPT { return std::addressof(__value_); }

private:
  _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
  _LIBCPP_NO_UNIQUE_ADDRESS __value_type __value_;
};

struct __shared_ptr_dummy_rebind_allocator_type;
template <>
class allocator<__shared_ptr_dummy_rebind_allocator_type> {
public:
  template <class _Other>
  struct rebind {
    typedef allocator<_Other> other;
  };
};

template <class _Tp>
class enable_shared_from_this;

// http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.general-6
// A pointer type Y* is said to be compatible with a pointer type T*
// when either Y* is convertible to T* or Y is U[N] and T is cv U[].
#if _LIBCPP_STD_VER >= 17
template <class _Yp, class _Tp>
inline const bool __bounded_convertible_to_unbounded_v = false;

template <class _Up, std::size_t _Np, class _Tp>
inline const bool __bounded_convertible_to_unbounded_v<_Up[_Np], _Tp> = is_same_v<remove_cv_t<_Tp>, _Up[]>;

template <class _Yp, class _Tp>
inline const bool __compatible_with_v = is_convertible_v<_Yp*, _Tp*> || __bounded_convertible_to_unbounded_v<_Yp, _Tp>;
#else
template <class _Yp, class _Tp>
inline const bool __compatible_with_v = is_convertible<_Yp*, _Tp*>::value;
#endif // _LIBCPP_STD_VER >= 17

// Constructors that take raw pointers have a different set of "compatible" constraints
// http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.const-9.1
// - If T is an array type, then either T is U[N] and Y(*)[N] is convertible to T*,
//   or T is U[] and Y(*)[] is convertible to T*.
// - If T is not an array type, then Y* is convertible to T*.
#if _LIBCPP_STD_VER >= 17
template <class _Yp, class _Tp, class = void>
inline const bool __raw_pointer_compatible_with_v = !is_array_v<_Tp> && is_convertible_v<_Yp*, _Tp*>;

template <class _Yp, class _Up, std::size_t _Np>
inline const bool
    __raw_pointer_compatible_with_v<_Yp, _Up[_Np], enable_if_t<is_convertible_v<_Yp (*)[_Np], _Up (*)[_Np]>>> = true;

template <class _Yp, class _Up>
inline const bool __raw_pointer_compatible_with_v<_Yp, _Up[], enable_if_t<is_convertible_v<_Yp (*)[], _Up (*)[]>>> =
    true;

#else
template <class _Yp, class _Tp>
inline const bool __raw_pointer_compatible_with_v = is_convertible<_Yp*, _Tp*>::value;
#endif // _LIBCPP_STD_VER >= 17

template <class _Ptr, class = void>
inline const bool __is_deletable_v = false;
template <class _Ptr>
inline const bool __is_deletable_v<_Ptr, decltype(delete std::declval<_Ptr>())> = true;

template <class _Ptr, class = void>
inline const bool __is_array_deletable_v = false;
template <class _Ptr>
inline const bool __is_array_deletable_v<_Ptr, decltype(delete[] std::declval<_Ptr>())> = true;

template <class _Dp, class _Pt, class = void>
inline const bool __well_formed_deleter_v = false;

template <class _Dp, class _Pt>
inline const bool __well_formed_deleter_v<_Dp, _Pt, __void_t<decltype(std::declval<_Dp>()(std::declval<_Pt>()))> > =
    true;

template <class _Dp, class _Yp, class _Tp>
inline const bool __shared_ptr_deleter_ctor_reqs_v =
    __raw_pointer_compatible_with_v<_Yp, _Tp> && is_move_constructible<_Dp>::value &&
    __well_formed_deleter_v<_Dp, _Yp*>;

template <class _Dp>
inline const bool __shared_ptr_nullptr_deleter_ctor_reqs_v =
    is_move_constructible<_Dp>::value && __well_formed_deleter_v<_Dp, nullptr_t>;

#if defined(_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI)
#  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI __attribute__((__trivial_abi__))
#else
#  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI
#endif

template <class _Tp>
class _LIBCPP_SHARED_PTR_TRIVIAL_ABI shared_ptr {
  struct __nullptr_sfinae_tag {};

public:
#if _LIBCPP_STD_VER >= 17
  typedef weak_ptr<_Tp> weak_type;
  typedef remove_extent_t<_Tp> element_type;
#else
  typedef _Tp element_type;
#endif

  // A shared_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
  // any bookkeeping, so it's always trivially relocatable.
  using __trivially_relocatable _LIBCPP_NODEBUG = shared_ptr;

private:
  element_type* __ptr_;
  __shared_weak_count* __cntrl_;

public:
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr(nullptr_t) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}

  template <class _Yp,
            __enable_if_t<__raw_pointer_compatible_with_v<_Yp, _Tp>
  // In C++03 we get errors when trying to do SFINAE with the
  // delete operator, so we always pretend that it's deletable.
  // The same happens on GCC.
#if !defined(_LIBCPP_CXX03_LANG)
                              && (is_array<_Tp>::value ? __is_array_deletable_v<_Yp*> : __is_deletable_v<_Yp*>)
#endif
                              ,
                          int> = 0>
  _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(_Yp* __p) : __ptr_(__p) {
    unique_ptr<_Yp> __hold(__p);
    typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
    typedef __shared_ptr_pointer<_Yp*, __shared_ptr_default_delete<_Tp, _Yp>, _AllocT> _CntrlBlk;
    __cntrl_ = new _CntrlBlk(__p, __shared_ptr_default_delete<_Tp, _Yp>(), _AllocT());
    __hold.release();
    __enable_weak_this(__p, __p);
  }

  template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs_v<_Dp, _Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d) : __ptr_(__p) {
    auto __guard = std::__make_exception_guard([&] { __d(__p); });
    typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
    typedef __shared_ptr_pointer<_Yp*, _Dp, _AllocT> _CntrlBlk;
#ifndef _LIBCPP_CXX03_LANG
    __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
#else
    __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
#endif // not _LIBCPP_CXX03_LANG
    __enable_weak_this(__p, __p);
    __guard.__complete();
  }

  template <class _Yp, class _Dp, class _Alloc, __enable_if_t<__shared_ptr_deleter_ctor_reqs_v<_Dp, _Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d, _Alloc __a) : __ptr_(__p) {
    auto __guard = std::__make_exception_guard([&] { __d(__p); });
    typedef __shared_ptr_pointer<_Yp*, _Dp, _Alloc> _CntrlBlk;
    typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
    typedef __allocator_destructor<_A2> _D2;
    _A2 __a2(__a);
    unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
    ::new ((void*)std::addressof(*__hold2.get()))
#ifndef _LIBCPP_CXX03_LANG
        _CntrlBlk(__p, std::move(__d), __a);
#else
        _CntrlBlk(__p, __d, __a);
#endif // not _LIBCPP_CXX03_LANG
    __cntrl_ = std::addressof(*__hold2.release());
    __enable_weak_this(__p, __p);
    __guard.__complete();
  }

  template <class _Dp>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(
      nullptr_t __p,
      _Dp __d,
      __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs_v<_Dp>, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
      : __ptr_(nullptr) {
    auto __guard = std::__make_exception_guard([&] { __d(__p); });
    typedef typename __shared_ptr_default_allocator<_Tp>::type _AllocT;
    typedef __shared_ptr_pointer<nullptr_t, _Dp, _AllocT> _CntrlBlk;
#ifndef _LIBCPP_CXX03_LANG
    __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
#else
    __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
#endif // not _LIBCPP_CXX03_LANG
    __guard.__complete();
  }

  template <class _Dp, class _Alloc>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(
      nullptr_t __p,
      _Dp __d,
      _Alloc __a,
      __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs_v<_Dp>, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
      : __ptr_(nullptr) {
    auto __guard = std::__make_exception_guard([&] { __d(__p); });
    typedef __shared_ptr_pointer<nullptr_t, _Dp, _Alloc> _CntrlBlk;
    typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
    typedef __allocator_destructor<_A2> _D2;
    _A2 __a2(__a);
    unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
    ::new ((void*)std::addressof(*__hold2.get()))
#ifndef _LIBCPP_CXX03_LANG
        _CntrlBlk(__p, std::move(__d), __a);
#else
        _CntrlBlk(__p, __d, __a);
#endif // not _LIBCPP_CXX03_LANG
    __cntrl_ = std::addressof(*__hold2.release());
    __guard.__complete();
  }

  template <class _Yp>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) _NOEXCEPT
      : __ptr_(__p),
        __cntrl_(__r.__cntrl_) {
    if (__cntrl_)
      __cntrl_->__add_shared();
  }

// LWG-2996
// We don't backport because it is an evolutionary change.
#if _LIBCPP_STD_VER >= 20
  template <class _Yp>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
      : __ptr_(__p), __cntrl_(__r.__cntrl_) {
    __r.__ptr_   = nullptr;
    __r.__cntrl_ = nullptr;
  }
#endif

  _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
    if (__cntrl_)
      __cntrl_->__add_shared();
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
    if (__cntrl_)
      __cntrl_->__add_shared();
  }

  _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
    __r.__ptr_   = nullptr;
    __r.__cntrl_ = nullptr;
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
    __r.__ptr_   = nullptr;
    __r.__cntrl_ = nullptr;
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(const weak_ptr<_Yp>& __r)
      : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_ ? __r.__cntrl_->lock() : __r.__cntrl_) {
    if (__cntrl_ == nullptr)
      std::__throw_bad_weak_ptr();
  }

#if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
  template <class _Yp, __enable_if_t<is_convertible<_Yp*, element_type*>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(auto_ptr<_Yp>&& __r) : __ptr_(__r.get()) {
    typedef __shared_ptr_pointer<_Yp*, default_delete<_Yp>, allocator<__remove_cv_t<_Yp> > > _CntrlBlk;
    __cntrl_ = new _CntrlBlk(__r.get(), default_delete<_Yp>(), allocator<__remove_cv_t<_Yp> >());
    __enable_weak_this(__r.get(), __r.get());
    __r.release();
  }
#endif

  template <class _Yp,
            class _Dp,
            __enable_if_t<__compatible_with_v<_Yp, _Tp> &&
                              is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
                          int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
    using _AllocT   = typename __shared_ptr_default_allocator<_Yp>::type;
    using _Deleter  = _If<is_lvalue_reference<_Dp>::value, reference_wrapper<__libcpp_remove_reference_t<_Dp> >, _Dp>;
    using _CntrlBlk = __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer, _Deleter, _AllocT>;

    __cntrl_ = __ptr_ ? new _CntrlBlk(__r.get(), std::forward<_Dp>(__r.get_deleter()), _AllocT()) : nullptr;
    __enable_weak_this(__r.get(), __r.get());
    __r.release();
  }

  _LIBCPP_HIDE_FROM_ABI ~shared_ptr() {
    if (__cntrl_)
      __cntrl_->__release_shared();
  }

  _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr& __r) _NOEXCEPT {
    shared_ptr(__r).swap(*this);
    return *this;
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr<_Yp>& __r) _NOEXCEPT {
    shared_ptr(__r).swap(*this);
    return *this;
  }

  _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr&& __r) _NOEXCEPT {
    shared_ptr(std::move(__r)).swap(*this);
    return *this;
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr<_Yp>&& __r) {
    shared_ptr(std::move(__r)).swap(*this);
    return *this;
  }

#if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
  template <class _Yp,
            __enable_if_t<!is_array<_Yp>::value && is_convertible<_Yp*, typename shared_ptr<_Tp>::element_type*>::value,
                          int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(auto_ptr<_Yp>&& __r) {
    shared_ptr(std::move(__r)).swap(*this);
    return *this;
  }
#endif

  template <class _Yp,
            class _Dp,
            __enable_if_t<__compatible_with_v<_Yp, _Tp> &&
                              is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
                          int> = 0>
  _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(unique_ptr<_Yp, _Dp>&& __r) {
    shared_ptr(std::move(__r)).swap(*this);
    return *this;
  }

  _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr& __r) _NOEXCEPT {
    std::swap(__ptr_, __r.__ptr_);
    std::swap(__cntrl_, __r.__cntrl_);
  }

  _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT { shared_ptr().swap(*this); }

  template <class _Yp, __enable_if_t<__raw_pointer_compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p) {
    shared_ptr(__p).swap(*this);
  }

  template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs_v<_Dp, _Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d) {
    shared_ptr(__p, __d).swap(*this);
  }

  template <class _Yp, class _Dp, class _Alloc, __enable_if_t<__shared_ptr_deleter_ctor_reqs_v<_Dp, _Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d, _Alloc __a) {
    shared_ptr(__p, __d, __a).swap(*this);
  }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI element_type* get() const _NOEXCEPT { return __ptr_; }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator*() const _NOEXCEPT {
    return *__ptr_;
  }

  _LIBCPP_HIDE_FROM_ABI element_type* operator->() const _NOEXCEPT {
    static_assert(!is_array<_Tp>::value, "std::shared_ptr<T>::operator-> is only valid when T is not an array type.");
    return __ptr_;
  }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT {
    return __cntrl_ ? __cntrl_->use_count() : 0;
  }

#if _LIBCPP_STD_VER < 20 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_SHARED_PTR_UNIQUE)
  [[__nodiscard__]] _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI bool unique() const _NOEXCEPT {
    return use_count() == 1;
  }
#endif

  _LIBCPP_HIDE_FROM_ABI explicit operator bool() const _NOEXCEPT { return get() != nullptr; }

  template <class _Up>
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool owner_before(shared_ptr<_Up> const& __p) const _NOEXCEPT {
    return __cntrl_ < __p.__cntrl_;
  }

  template <class _Up>
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool owner_before(weak_ptr<_Up> const& __p) const _NOEXCEPT {
    return __cntrl_ < __p.__cntrl_;
  }

  _LIBCPP_HIDE_FROM_ABI bool __owner_equivalent(const shared_ptr& __p) const { return __cntrl_ == __p.__cntrl_; }

#if _LIBCPP_STD_VER >= 17
  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator[](ptrdiff_t __i) const {
    static_assert(is_array<_Tp>::value, "std::shared_ptr<T>::operator[] is only valid when T is an array type.");
    return __ptr_[__i];
  }
#endif

#if _LIBCPP_HAS_RTTI
  template <class _Dp>
  _LIBCPP_HIDE_FROM_ABI _Dp* __get_deleter() const _NOEXCEPT {
    return static_cast<_Dp*>(__cntrl_ ? const_cast<void*>(__cntrl_->__get_deleter(typeid(_Dp))) : nullptr);
  }
#endif // _LIBCPP_HAS_RTTI

  template <class _Yp, class _CntrlBlk>
  _LIBCPP_HIDE_FROM_ABI static shared_ptr<_Tp> __create_with_control_block(_Yp* __p, _CntrlBlk* __cntrl) _NOEXCEPT {
    shared_ptr<_Tp> __r;
    __r.__ptr_   = __p;
    __r.__cntrl_ = __cntrl;
    __r.__enable_weak_this(__r.__ptr_, __r.__ptr_);
    return __r;
  }

private:
  template <class _Yp, bool = is_function<_Yp>::value>
  struct __shared_ptr_default_allocator {
    typedef allocator<__remove_cv_t<_Yp> > type;
  };

  template <class _Yp>
  struct __shared_ptr_default_allocator<_Yp, true> {
    typedef allocator<__shared_ptr_dummy_rebind_allocator_type> type;
  };

  template <class _Yp,
            class _OrigPtr,
            __enable_if_t<is_convertible<_OrigPtr*, const enable_shared_from_this<_Yp>*>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(const enable_shared_from_this<_Yp>* __e, _OrigPtr* __ptr) _NOEXCEPT {
    typedef __remove_cv_t<_Yp> _RawYp;
    if (__e && __e->__weak_this_.expired()) {
      __e->__weak_this_ = shared_ptr<_RawYp>(*this, const_cast<_RawYp*>(static_cast<const _Yp*>(__ptr)));
    }
  }

  template <class _Vp>
  static __type_identity<_Vp> __get_shared_from_this_impl(const enable_shared_from_this<_Vp>*);

  template <class _Vp, class = void>
  struct __get_shared_from_this {
    using type _LIBCPP_NODEBUG = __nat;
  };

  template <class _Vp>
  struct __get_shared_from_this<_Vp, __void_t<decltype(__get_shared_from_this_impl(static_cast<_Vp*>(nullptr)))> > {
    using type _LIBCPP_NODEBUG = const enable_shared_from_this<typename decltype(__get_shared_from_this_impl(
        static_cast<_Vp*>(nullptr)))::type>*;
  };

  template <
      class _Yp,
      class _OrigPtr,
      __enable_if_t<!is_convertible<_OrigPtr, typename __get_shared_from_this<__remove_pointer_t<_Yp> >::type>::value,
                    int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(_Yp, _OrigPtr) {}

  template <class, class _Yp>
  struct __shared_ptr_default_delete : default_delete<_Yp> {};

  template <class _Yp, class _Un, size_t _Sz>
  struct __shared_ptr_default_delete<_Yp[_Sz], _Un> : default_delete<_Yp[]> {};

  template <class _Yp, class _Un>
  struct __shared_ptr_default_delete<_Yp[], _Un> : default_delete<_Yp[]> {};

  template <class _Up>
  friend class shared_ptr;
  template <class _Up>
  friend class weak_ptr;
};

#if _LIBCPP_STD_VER >= 17
template <class _Tp>
shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
template <class _Tp, class _Dp>
shared_ptr(unique_ptr<_Tp, _Dp>) -> shared_ptr<_Tp>;
#endif

//
// std::allocate_shared and std::make_shared
//

template <class _ControlBlock, class _Tp, class _Alloc, class... _Args>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> __allocate_shared_impl(const _Alloc& __alloc, _Args&&... __args) {
  using _ControlBlockAllocator = typename __allocator_traits_rebind<_Alloc, _ControlBlock>::type;
  __allocation_guard<_ControlBlockAllocator> __guard(__alloc, 1);
  ::new ((void*)std::addressof(*__guard.__get())) _ControlBlock(__alloc, std::forward<_Args>(__args)...);
  auto __control_block = __guard.__release_ptr();
  return shared_ptr<_Tp>::__create_with_control_block(
      __control_block->__get_elem(), std::__to_address(__control_block));
}

template <class _Tp, class _Alloc, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, _Args&&... __args) {
  using _CanonicalAlloc = __allocator_traits_rebind_t<_Alloc, __remove_cv_t<_Tp> >;
  using _ControlBlock   = __shared_ptr_emplace<_Tp, _CanonicalAlloc>;
  return std::__allocate_shared_impl<_ControlBlock, _Tp>(_CanonicalAlloc(__a), std::forward<_Args>(__args)...);
}

template <class _Tp, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(_Args&&... __args) {
  return std::allocate_shared<_Tp>(allocator<__remove_cv_t<_Tp> >(), std::forward<_Args>(__args)...);
}

#if _LIBCPP_STD_VER >= 20

template <class _Tp, class _Alloc, __enable_if_t<!is_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
  using _CanonicalAlloc = __allocator_traits_rebind_t<_Alloc, remove_cv_t<_Tp>>;
  using _ControlBlock   = __shared_ptr_emplace_for_overwrite<_Tp, _CanonicalAlloc>;
  return std::__allocate_shared_impl<_ControlBlock, _Tp>(_CanonicalAlloc(__a));
}

template <class _Tp, __enable_if_t<!is_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
  return std::allocate_shared_for_overwrite<_Tp>(allocator<__remove_cv_t<_Tp>>());
}

#endif // _LIBCPP_STD_VER >= 20

#if _LIBCPP_STD_VER >= 17

template <size_t _Alignment>
struct __sp_aligned_storage {
  alignas(_Alignment) char __storage[_Alignment];
};

template <class _Tp, class _Alloc>
struct __unbounded_array_control_block;

template <class _Tp, class _Alloc>
struct __unbounded_array_control_block<_Tp[], _Alloc> : __shared_weak_count {
  _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }

  _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(
      _Alloc const& __alloc, size_t __count, _Tp const& __arg)
      : __alloc_(__alloc), __count_(__count) {
    std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::begin(__data_), __count_, __arg);
  }

  _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(_Alloc const& __alloc, size_t __count)
      : __alloc_(__alloc), __count_(__count) {
#  if _LIBCPP_STD_VER >= 20
    if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
      // We are purposefully not using an allocator-aware default construction because the spec says so.
      // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
      std::uninitialized_default_construct_n(std::begin(__data_), __count_);
    } else {
      std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
    }
#  else
    std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
#  endif
  }

  // Returns the number of bytes required to store a control block followed by the given number
  // of elements of _Tp, with the whole storage being aligned to a multiple of _Tp's alignment.
  _LIBCPP_HIDE_FROM_ABI static constexpr size_t __bytes_for(size_t __elements) {
    // When there's 0 elements, the control block alone is enough since it holds one element.
    // Otherwise, we allocate one fewer element than requested because the control block already
    // holds one. Also, we use the bitwise formula below to ensure that we allocate enough bytes
    // for the whole allocation to be a multiple of _Tp's alignment. That formula is taken from [1].
    //
    // [1]: https://en.wikipedia.org/wiki/Data_structure_alignment#Computing_padding
    size_t __bytes           = __elements == 0 ? sizeof(__unbounded_array_control_block)
                                               : (__elements - 1) * sizeof(_Tp) + sizeof(__unbounded_array_control_block);
    constexpr size_t __align = alignof(__unbounded_array_control_block);
    return (__bytes + __align - 1) & ~(__align - 1);
  }

  _LIBCPP_HIDE_FROM_ABI_VIRTUAL
  ~__unbounded_array_control_block() override {
  } // can't be `= default` because of the sometimes-non-trivial union member __data_

private:
  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
#  if _LIBCPP_STD_VER >= 20
    if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
      std::__reverse_destroy(__data_, __data_ + __count_);
    } else {
      __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
      std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
    }
#  else
    __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
    std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
#  endif
  }

  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
    using _AlignedStorage = __sp_aligned_storage<alignof(__unbounded_array_control_block)>;
    using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
    using _PointerTraits  = pointer_traits<typename allocator_traits<_StorageAlloc>::pointer>;

    _StorageAlloc __tmp(__alloc_);
    __alloc_.~_Alloc();
    size_t __size              = __unbounded_array_control_block::__bytes_for(__count_);
    _AlignedStorage* __storage = reinterpret_cast<_AlignedStorage*>(this);
    allocator_traits<_StorageAlloc>::deallocate(
        __tmp, _PointerTraits::pointer_to(*__storage), __size / sizeof(_AlignedStorage));
  }

  _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
  size_t __count_;
  union {
    _Tp __data_[1];
  };
};

template <class _Array, class _Alloc, class... _Arg>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Array>
__allocate_shared_unbounded_array(const _Alloc& __a, size_t __n, _Arg&&... __arg) {
  static_assert(__is_unbounded_array_v<_Array>);
  // We compute the number of bytes necessary to hold the control block and the
  // array elements. Then, we allocate an array of properly-aligned dummy structs
  // large enough to hold the control block and array. This allows shifting the
  // burden of aligning memory properly from us to the allocator.
  using _ControlBlock   = __unbounded_array_control_block<_Array, _Alloc>;
  using _AlignedStorage = __sp_aligned_storage<alignof(_ControlBlock)>;
  using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
  __allocation_guard<_StorageAlloc> __guard(__a, _ControlBlock::__bytes_for(__n) / sizeof(_AlignedStorage));
  _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
  std::__construct_at(__control_block, __a, __n, std::forward<_Arg>(__arg)...);
  __guard.__release_ptr();
  return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
}

template <class _Tp, class _Alloc>
struct __bounded_array_control_block;

template <class _Tp, size_t _Count, class _Alloc>
struct __bounded_array_control_block<_Tp[_Count], _Alloc> : __shared_weak_count {
  _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }

  _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc, _Tp const& __arg)
      : __alloc_(__alloc) {
    std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count, __arg);
  }

  _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc) : __alloc_(__alloc) {
#  if _LIBCPP_STD_VER >= 20
    if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
      // We are purposefully not using an allocator-aware default construction because the spec says so.
      // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
      std::uninitialized_default_construct_n(std::addressof(__data_[0]), _Count);
    } else {
      std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
    }
#  else
    std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
#  endif
  }

  _LIBCPP_HIDE_FROM_ABI_VIRTUAL
  ~__bounded_array_control_block() override {
  } // can't be `= default` because of the sometimes-non-trivial union member __data_

private:
  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
#  if _LIBCPP_STD_VER >= 20
    if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
      std::__reverse_destroy(__data_, __data_ + _Count);
    } else {
      __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
      std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
    }
#  else
    __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
    std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
#  endif
  }

  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
    using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, __bounded_array_control_block>;
    using _PointerTraits     = pointer_traits<typename allocator_traits<_ControlBlockAlloc>::pointer>;

    _ControlBlockAlloc __tmp(__alloc_);
    __alloc_.~_Alloc();
    allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, _PointerTraits::pointer_to(*this), 1);
  }

  _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
  union {
    _Tp __data_[_Count];
  };
};

template <class _Array, class _Alloc, class... _Arg>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Array> __allocate_shared_bounded_array(const _Alloc& __a, _Arg&&... __arg) {
  static_assert(__is_bounded_array_v<_Array>);
  using _ControlBlock      = __bounded_array_control_block<_Array, _Alloc>;
  using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, _ControlBlock>;

  __allocation_guard<_ControlBlockAlloc> __guard(__a, 1);
  _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
  std::__construct_at(__control_block, __a, std::forward<_Arg>(__arg)...);
  __guard.__release_ptr();
  return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
}

#endif // _LIBCPP_STD_VER >= 17

#if _LIBCPP_STD_VER >= 20

// bounded array variants
template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a) {
  return std::__allocate_shared_bounded_array<_Tp>(__a);
}

template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
allocate_shared(const _Alloc& __a, const remove_extent_t<_Tp>& __u) {
  return std::__allocate_shared_bounded_array<_Tp>(__a, __u);
}

template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
  using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
  _ForOverwriteAllocator __alloc(__a);
  return std::__allocate_shared_bounded_array<_Tp>(__alloc);
}

template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared() {
  return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>());
}

template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(const remove_extent_t<_Tp>& __u) {
  return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>(), __u);
}

template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
  return std::__allocate_shared_bounded_array<_Tp>(allocator<__for_overwrite_tag>());
}

// unbounded array variants
template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n) {
  return std::__allocate_shared_unbounded_array<_Tp>(__a, __n);
}

template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
allocate_shared(const _Alloc& __a, size_t __n, const remove_extent_t<_Tp>& __u) {
  return std::__allocate_shared_unbounded_array<_Tp>(__a, __n, __u);
}

template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a, size_t __n) {
  using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
  _ForOverwriteAllocator __alloc(__a);
  return std::__allocate_shared_unbounded_array<_Tp>(__alloc, __n);
}

template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n) {
  return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n);
}

template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n, const remove_extent_t<_Tp>& __u) {
  return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n, __u);
}

template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite(size_t __n) {
  return std::__allocate_shared_unbounded_array<_Tp>(allocator<__for_overwrite_tag>(), __n);
}

#endif // _LIBCPP_STD_VER >= 20

template <class _Tp, class _Up>
inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
  return __x.get() == __y.get();
}

#if _LIBCPP_STD_VER <= 17

template <class _Tp, class _Up>
inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
  return !(__x == __y);
}

template <class _Tp, class _Up>
inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
#  if _LIBCPP_STD_VER <= 11
  typedef typename common_type<_Tp*, _Up*>::type _Vp;
  return less<_Vp>()(__x.get(), __y.get());
#  else
  return less<>()(__x.get(), __y.get());
#  endif
}

template <class _Tp, class _Up>
inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
  return __y < __x;
}

template <class _Tp, class _Up>
inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
  return !(__y < __x);
}

template <class _Tp, class _Up>
inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
  return !(__x < __y);
}

#endif // _LIBCPP_STD_VER <= 17

#if _LIBCPP_STD_VER >= 20
template <class _Tp, class _Up>
_LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) noexcept {
  return compare_three_way()(__x.get(), __y.get());
}
#endif

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
  return !__x;
}

#if _LIBCPP_STD_VER <= 17

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator==(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
  return !__x;
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
  return static_cast<bool>(__x);
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator!=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
  return static_cast<bool>(__x);
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
  return less<typename shared_ptr<_Tp>::element_type*>()(__x.get(), nullptr);
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator<(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
  return less<typename shared_ptr<_Tp>::element_type*>()(nullptr, __x.get());
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
  return nullptr < __x;
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator>(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
  return __x < nullptr;
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
  return !(nullptr < __x);
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator<=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
  return !(__x < nullptr);
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
  return !(__x < nullptr);
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator>=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
  return !(nullptr < __x);
}

#endif // _LIBCPP_STD_VER <= 17

#if _LIBCPP_STD_VER >= 20
template <class _Tp>
_LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, nullptr_t) noexcept {
  return compare_three_way()(__x.get(), static_cast<typename shared_ptr<_Tp>::element_type*>(nullptr));
}
#endif

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr<_Tp>& __x, shared_ptr<_Tp>& __y) _NOEXCEPT {
  __x.swap(__y);
}

template <class _Tp, class _Up>
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
static_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
  return shared_ptr<_Tp>(__r, static_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
}

// LWG-2996
// We don't backport because it is an evolutionary change.
#if _LIBCPP_STD_VER >= 20
template <class _Tp, class _Up>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
  return shared_ptr<_Tp>(std::move(__r), static_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
}
#endif

template <class _Tp, class _Up>
[[__nodiscard__]] inline
    _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
  typedef typename shared_ptr<_Tp>::element_type _ET;
  _ET* __p = dynamic_cast<_ET*>(__r.get());
  return __p ? shared_ptr<_Tp>(__r, __p) : shared_ptr<_Tp>();
}

// LWG-2996
// We don't backport because it is an evolutionary change.
#if _LIBCPP_STD_VER >= 20
template <class _Tp, class _Up>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
  auto* __p = dynamic_cast<typename shared_ptr<_Tp>::element_type*>(__r.get());
  return __p ? shared_ptr<_Tp>(std::move(__r), __p) : shared_ptr<_Tp>();
}
#endif

template <class _Tp, class _Up>
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
  typedef typename shared_ptr<_Tp>::element_type _RTp;
  return shared_ptr<_Tp>(__r, const_cast<_RTp*>(__r.get()));
}

// LWG-2996
// We don't backport because it is an evolutionary change.
#if _LIBCPP_STD_VER >= 20
template <class _Tp, class _Up>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
  return shared_ptr<_Tp>(std::move(__r), const_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
}
#endif

template <class _Tp, class _Up>
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
  return shared_ptr<_Tp>(__r, reinterpret_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
}

// LWG-2996
// We don't backport because it is an evolutionary change.
#if _LIBCPP_STD_VER >= 20
template <class _Tp, class _Up>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
  return shared_ptr<_Tp>(std::move(__r), reinterpret_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
}
#endif

#if _LIBCPP_HAS_RTTI

template <class _Dp, class _Tp>
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _Dp* get_deleter(const shared_ptr<_Tp>& __p) _NOEXCEPT {
  return __p.template __get_deleter<_Dp>();
}

#endif // _LIBCPP_HAS_RTTI

template <class _Tp>
class _LIBCPP_SHARED_PTR_TRIVIAL_ABI weak_ptr {
public:
#if _LIBCPP_STD_VER >= 17
  typedef remove_extent_t<_Tp> element_type;
#else
  typedef _Tp element_type;
#endif

  // A weak_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
  // any bookkeeping, so it's always trivially relocatable.
  using __trivially_relocatable _LIBCPP_NODEBUG = weak_ptr;

private:
  element_type* __ptr_;
  __shared_weak_count* __cntrl_;

public:
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR weak_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
    if (__cntrl_)
      __cntrl_->__add_weak();
  }

  _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
    if (__cntrl_)
      __cntrl_->__add_weak();
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
    shared_ptr<_Yp> __s = __r.lock();
    *this               = weak_ptr<_Tp>(__s);
  }

  _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
    __r.__ptr_   = nullptr;
    __r.__cntrl_ = nullptr;
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
    shared_ptr<_Yp> __s = __r.lock();
    *this               = weak_ptr<_Tp>(__s);
    __r.reset();
  }

  _LIBCPP_HIDE_FROM_ABI ~weak_ptr() {
    if (__cntrl_)
      __cntrl_->__release_weak();
  }

  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr const& __r) _NOEXCEPT {
    weak_ptr(__r).swap(*this);
    return *this;
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT {
    weak_ptr(__r).swap(*this);
    return *this;
  }

  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr&& __r) _NOEXCEPT {
    weak_ptr(std::move(__r)).swap(*this);
    return *this;
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT {
    weak_ptr(std::move(__r)).swap(*this);
    return *this;
  }

  template <class _Yp, __enable_if_t<__compatible_with_v<_Yp, _Tp>, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT {
    weak_ptr(__r).swap(*this);
    return *this;
  }

  _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr& __r) _NOEXCEPT {
    std::swap(__ptr_, __r.__ptr_);
    std::swap(__cntrl_, __r.__cntrl_);
  }

  _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT { weak_ptr().swap(*this); }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT {
    return __cntrl_ ? __cntrl_->use_count() : 0;
  }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool expired() const _NOEXCEPT {
    return __cntrl_ == nullptr || __cntrl_->use_count() == 0;
  }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> lock() const _NOEXCEPT {
    shared_ptr<_Tp> __r;
    __r.__cntrl_ = __cntrl_ ? __cntrl_->lock() : __cntrl_;
    if (__r.__cntrl_)
      __r.__ptr_ = __ptr_;
    return __r;
  }

  template <class _Up>
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool owner_before(const shared_ptr<_Up>& __r) const _NOEXCEPT {
    return __cntrl_ < __r.__cntrl_;
  }
  template <class _Up>
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool owner_before(const weak_ptr<_Up>& __r) const _NOEXCEPT {
    return __cntrl_ < __r.__cntrl_;
  }

  template <class _Up>
  friend class weak_ptr;
  template <class _Up>
  friend class shared_ptr;
};

#if _LIBCPP_STD_VER >= 17
template <class _Tp>
weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
#endif

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr<_Tp>& __x, weak_ptr<_Tp>& __y) _NOEXCEPT {
  __x.swap(__y);
}

#if _LIBCPP_STD_VER >= 17
template <class _Tp = void>
struct owner_less;
#else
template <class _Tp>
struct owner_less;
#endif

template <class _Tp>
struct owner_less<shared_ptr<_Tp> > : __binary_function<shared_ptr<_Tp>, shared_ptr<_Tp>, bool> {
  _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
  _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
  _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
};

template <class _Tp>
struct owner_less<weak_ptr<_Tp> > : __binary_function<weak_ptr<_Tp>, weak_ptr<_Tp>, bool> {
  _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
  _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
  _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
};

#if _LIBCPP_STD_VER >= 17
template <>
struct owner_less<void> {
  template <class _Tp, class _Up>
  _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
  template <class _Tp, class _Up>
  _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
  template <class _Tp, class _Up>
  _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
  template <class _Tp, class _Up>
  _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
    return __x.owner_before(__y);
  }
  typedef void is_transparent;
};
#endif

template <class _Tp>
class enable_shared_from_this {
  mutable weak_ptr<_Tp> __weak_this_;

protected:
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR enable_shared_from_this() _NOEXCEPT {}
  _LIBCPP_HIDE_FROM_ABI enable_shared_from_this(enable_shared_from_this const&) _NOEXCEPT {}
  _LIBCPP_HIDE_FROM_ABI enable_shared_from_this& operator=(enable_shared_from_this const&) _NOEXCEPT { return *this; }
  _LIBCPP_HIDE_FROM_ABI ~enable_shared_from_this() {}

public:
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> shared_from_this() { return shared_ptr<_Tp>(__weak_this_); }
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp const> shared_from_this() const {
    return shared_ptr<const _Tp>(__weak_this_);
  }

#if _LIBCPP_STD_VER >= 17
  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI weak_ptr<_Tp> weak_from_this() _NOEXCEPT { return __weak_this_; }

  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI weak_ptr<const _Tp> weak_from_this() const _NOEXCEPT { return __weak_this_; }
#endif // _LIBCPP_STD_VER >= 17

  template <class _Up>
  friend class shared_ptr;
};

template <class _Tp>
struct hash;

template <class _Tp>
struct hash<shared_ptr<_Tp> > {
#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_BINDER_TYPEDEFS)
  _LIBCPP_DEPRECATED_IN_CXX17 typedef shared_ptr<_Tp> argument_type;
  _LIBCPP_DEPRECATED_IN_CXX17 typedef size_t result_type;
#endif

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_t operator()(const shared_ptr<_Tp>& __ptr) const _NOEXCEPT {
    return hash<typename shared_ptr<_Tp>::element_type*>()(__ptr.get());
  }
};

template <class _CharT, class _Traits, class _Yp>
inline _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, shared_ptr<_Yp> const& __p);

#if _LIBCPP_HAS_THREADS

class _LIBCPP_EXPORTED_FROM_ABI __sp_mut {
  void* __lx_;

public:
  void lock() _NOEXCEPT;
  void unlock() _NOEXCEPT;

private:
  _LIBCPP_CONSTEXPR __sp_mut(void*) _NOEXCEPT;
  __sp_mut(const __sp_mut&);
  __sp_mut& operator=(const __sp_mut&);

  friend _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
};

_LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool atomic_is_lock_free(const shared_ptr<_Tp>*) {
  return false;
}

template <class _Tp>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load(const shared_ptr<_Tp>* __p) {
  __sp_mut& __m = std::__get_sp_mut(__p);
  __m.lock();
  shared_ptr<_Tp> __q = *__p;
  __m.unlock();
  return __q;
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order) {
  return std::atomic_load(__p);
}

template <class _Tp>
_LIBCPP_HIDE_FROM_ABI void atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
  __sp_mut& __m = std::__get_sp_mut(__p);
  __m.lock();
  __p->swap(__r);
  __m.unlock();
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI void atomic_store_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
  std::atomic_store(__p, __r);
}

template <class _Tp>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
  __sp_mut& __m = std::__get_sp_mut(__p);
  __m.lock();
  __p->swap(__r);
  __m.unlock();
  return __r;
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
atomic_exchange_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
  return std::atomic_exchange(__p, __r);
}

template <class _Tp>
_LIBCPP_HIDE_FROM_ABI bool
atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
  shared_ptr<_Tp> __temp;
  __sp_mut& __m = std::__get_sp_mut(__p);
  __m.lock();
  if (__p->__owner_equivalent(*__v)) {
    std::swap(__temp, *__p);
    *__p = __w;
    __m.unlock();
    return true;
  }
  std::swap(__temp, *__v);
  *__v = *__p;
  __m.unlock();
  return false;
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool
atomic_compare_exchange_weak(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
  return std::atomic_compare_exchange_strong(__p, __v, __w);
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_strong_explicit(
    shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
  return std::atomic_compare_exchange_strong(__p, __v, __w);
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_weak_explicit(
    shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
  return std::atomic_compare_exchange_weak(__p, __v, __w);
}

#endif // _LIBCPP_HAS_THREADS

_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___MEMORY_SHARED_PTR_H