// -*- 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 <__availability>
#include <__compare/compare_three_way.h>
#include <__compare/ordering.h>
#include <__config>
#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/compressed_pair.h>
#include <__memory/construct_at.h>
#include <__memory/pointer_traits.h>
#include <__memory/uninitialized_algorithms.h>
#include <__memory/unique_ptr.h>
#include <__type_traits/add_lvalue_reference.h>
#include <__type_traits/conditional.h>
#include <__type_traits/conjunction.h>
#include <__type_traits/disjunction.h>
#include <__type_traits/is_array.h>
#include <__type_traits/is_bounded_array.h>
#include <__type_traits/is_convertible.h>
#include <__type_traits/is_move_constructible.h>
#include <__type_traits/is_reference.h>
#include <__type_traits/is_unbounded_array.h>
#include <__type_traits/nat.h>
#include <__type_traits/negation.h>
#include <__type_traits/remove_extent.h>
#include <__type_traits/remove_reference.h>
#include <__utility/declval.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <__utility/swap.h>
#include <__verbose_abort>
#include <cstddef>
#include <new>
#include <typeinfo>
#if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
#  include <__atomic/memory_order.h>
#endif

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

_LIBCPP_BEGIN_NAMESPACE_STD

// NOTE: Relaxed and acq/rel atomics (for increment and decrement respectively)
// should be sufficient for thread safety.
// See https://llvm.org/PR22803
#if defined(__clang__) && __has_builtin(__atomic_add_fetch) && defined(__ATOMIC_RELAXED) && defined(__ATOMIC_ACQ_REL)
#  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT
#elif defined(_LIBCPP_COMPILER_GCC)
#  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT
#endif

template <class _ValueType>
inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_relaxed_load(_ValueType const* __value) {
#if !defined(_LIBCPP_HAS_NO_THREADS) && defined(__ATOMIC_RELAXED) &&                                                   \
    (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
  return __atomic_load_n(__value, __ATOMIC_RELAXED);
#else
  return *__value;
#endif
}

template <class _ValueType>
inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_acquire_load(_ValueType const* __value) {
#if !defined(_LIBCPP_HAS_NO_THREADS) && defined(__ATOMIC_ACQUIRE) &&                                                   \
    (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
  return __atomic_load_n(__value, __ATOMIC_ACQUIRE);
#else
  return *__value;
#endif
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_increment(_Tp& __t) _NOEXCEPT {
#if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && !defined(_LIBCPP_HAS_NO_THREADS)
  return __atomic_add_fetch(&__t, 1, __ATOMIC_RELAXED);
#else
  return __t += 1;
#endif
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_decrement(_Tp& __t) _NOEXCEPT {
#if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && !defined(_LIBCPP_HAS_NO_THREADS)
  return __atomic_add_fetch(&__t, -1, __ATOMIC_ACQ_REL);
#else
  return __t -= 1;
#endif
}

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;
  const char* what() const _NOEXCEPT override;
};

_LIBCPP_NORETURN inline _LIBCPP_HIDE_FROM_ABI void __throw_bad_weak_ptr() {
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
  throw bad_weak_ptr();
#else
  _LIBCPP_VERBOSE_ABORT("bad_weak_ptr was thrown in -fno-exceptions mode");
#endif
}

template <class _Tp>
class _LIBCPP_TEMPLATE_VIS weak_ptr;

class _LIBCPP_EXPORTED_FROM_ABI __shared_count {
  __shared_count(const __shared_count&);
  __shared_count& operator=(const __shared_count&);

protected:
  long __shared_owners_;
  virtual ~__shared_count();

private:
  virtual void __on_zero_shared() _NOEXCEPT = 0;

public:
  _LIBCPP_HIDE_FROM_ABI explicit __shared_count(long __refs = 0) _NOEXCEPT : __shared_owners_(__refs) {}

#if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
  void __add_shared() noexcept;
  bool __release_shared() noexcept;
#else
  _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_owners_); }
  _LIBCPP_HIDE_FROM_ABI bool __release_shared() _NOEXCEPT {
    if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {
      __on_zero_shared();
      return true;
    }
    return false;
  }
#endif
  _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __libcpp_relaxed_load(&__shared_owners_) + 1; }
};

class _LIBCPP_EXPORTED_FROM_ABI __shared_weak_count : private __shared_count {
  long __shared_weak_owners_;

public:
  _LIBCPP_HIDE_FROM_ABI explicit __shared_weak_count(long __refs = 0) _NOEXCEPT
      : __shared_count(__refs),
        __shared_weak_owners_(__refs) {}

protected:
  ~__shared_weak_count() override;

public:
#if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
  void __add_shared() noexcept;
  void __add_weak() noexcept;
  void __release_shared() noexcept;
#else
  _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __shared_count::__add_shared(); }
  _LIBCPP_HIDE_FROM_ABI void __add_weak() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_weak_owners_); }
  _LIBCPP_HIDE_FROM_ABI void __release_shared() _NOEXCEPT {
    if (__shared_count::__release_shared())
      __release_weak();
  }
#endif
  void __release_weak() _NOEXCEPT;
  _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __shared_count::use_count(); }
  __shared_weak_count* lock() _NOEXCEPT;

  virtual const void* __get_deleter(const type_info&) const _NOEXCEPT;

private:
  virtual void __on_zero_shared_weak() _NOEXCEPT = 0;
};

template <class _Tp, class _Dp, class _Alloc>
class __shared_ptr_pointer : public __shared_weak_count {
  __compressed_pair<__compressed_pair<_Tp, _Dp>, _Alloc> __data_;

public:
  _LIBCPP_HIDE_FROM_ABI __shared_ptr_pointer(_Tp __p, _Dp __d, _Alloc __a)
      : __data_(__compressed_pair<_Tp, _Dp>(__p, std::move(__d)), std::move(__a)) {}

#ifndef _LIBCPP_HAS_NO_RTTI
  _LIBCPP_HIDE_FROM_ABI_VIRTUAL const void* __get_deleter(const type_info&) const _NOEXCEPT override;
#endif

private:
  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override;
  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override;
};

#ifndef _LIBCPP_HAS_NO_RTTI

template <class _Tp, class _Dp, class _Alloc>
const void* __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__get_deleter(const type_info& __t) const _NOEXCEPT {
  return __t == typeid(_Dp) ? std::addressof(__data_.first().second()) : nullptr;
}

#endif // _LIBCPP_HAS_NO_RTTI

template <class _Tp, class _Dp, class _Alloc>
void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared() _NOEXCEPT {
  __data_.first().second()(__data_.first().first());
  __data_.first().second().~_Dp();
}

template <class _Tp, class _Dp, class _Alloc>
void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared_weak() _NOEXCEPT {
  typedef typename __allocator_traits_rebind<_Alloc, __shared_ptr_pointer>::type _Al;
  typedef allocator_traits<_Al> _ATraits;
  typedef pointer_traits<typename _ATraits::pointer> _PTraits;

  _Al __a(__data_.second());
  __data_.second().~_Alloc();
  __a.deallocate(_PTraits::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 __shared_ptr_emplace : __shared_weak_count {
  template <class... _Args,
            class _Allocator                                                                         = _Alloc,
            __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&...) : __storage_(std::move(__a)) {
    static_assert(
        sizeof...(_Args) == 0, "No argument should be provided to the control block when using _for_overwrite");
    ::new ((void*)__get_elem()) _Tp;
  }

  template <class... _Args,
            class _Allocator                                                                          = _Alloc,
            __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&... __args) : __storage_(std::move(__a)) {
    using _TpAlloc = typename __allocator_traits_rebind<_Alloc, _Tp>::type;
    _TpAlloc __tmp(*__get_alloc());
    allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), std::forward<_Args>(__args)...);
  }

  _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT { return __storage_.__get_alloc(); }

  _LIBCPP_HIDE_FROM_ABI _Tp* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }

private:
  template <class _Allocator                                                                         = _Alloc,
            __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
    __get_elem()->~_Tp();
  }

  template <class _Allocator                                                                          = _Alloc,
            __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
    using _TpAlloc = typename __allocator_traits_rebind<_Allocator, _Tp>::type;
    _TpAlloc __tmp(*__get_alloc());
    allocator_traits<_TpAlloc>::destroy(__tmp, __get_elem());
  }

  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override { __on_zero_shared_impl(); }

  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
    using _ControlBlockAlloc   = typename __allocator_traits_rebind<_Alloc, __shared_ptr_emplace>::type;
    using _ControlBlockPointer = typename allocator_traits<_ControlBlockAlloc>::pointer;
    _ControlBlockAlloc __tmp(*__get_alloc());
    __storage_.~_Storage();
    allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, pointer_traits<_ControlBlockPointer>::pointer_to(*this), 1);
  }

  // This class implements the control block for non-array shared pointers created
  // through `std::allocate_shared` and `std::make_shared`.
  //
  // In previous versions of the library, we used a compressed pair to store
  // both the _Alloc and the _Tp. This implies using EBO, which is incompatible
  // with Allocator construction for _Tp. To allow implementing P0674 in C++20,
  // we now use a properly aligned char buffer while making sure that we maintain
  // the same layout that we had when we used a compressed pair.
  using _CompressedPair = __compressed_pair<_Alloc, _Tp>;
  struct _ALIGNAS_TYPE(_CompressedPair) _Storage {
    char __blob_[sizeof(_CompressedPair)];

    _LIBCPP_HIDE_FROM_ABI explicit _Storage(_Alloc&& __a) { ::new ((void*)__get_alloc()) _Alloc(std::move(__a)); }
    _LIBCPP_HIDE_FROM_ABI ~_Storage() { __get_alloc()->~_Alloc(); }
    _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT {
      _CompressedPair* __as_pair                = reinterpret_cast<_CompressedPair*>(__blob_);
      typename _CompressedPair::_Base1* __first = _CompressedPair::__get_first_base(__as_pair);
      _Alloc* __alloc                           = reinterpret_cast<_Alloc*>(__first);
      return __alloc;
    }
    _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _Tp* __get_elem() _NOEXCEPT {
      _CompressedPair* __as_pair                 = reinterpret_cast<_CompressedPair*>(__blob_);
      typename _CompressedPair::_Base2* __second = _CompressedPair::__get_second_base(__as_pair);
      _Tp* __elem                                = reinterpret_cast<_Tp*>(__second);
      return __elem;
    }
  };

  static_assert(_LIBCPP_ALIGNOF(_Storage) == _LIBCPP_ALIGNOF(_CompressedPair), "");
  static_assert(sizeof(_Storage) == sizeof(_CompressedPair), "");
  _Storage __storage_;
};

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

template <class _Tp>
class _LIBCPP_TEMPLATE_VIS 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>
struct __bounded_convertible_to_unbounded : false_type {};

template <class _Up, std::size_t _Np, class _Tp>
struct __bounded_convertible_to_unbounded<_Up[_Np], _Tp> : is_same<__remove_cv_t<_Tp>, _Up[]> {};

template <class _Yp, class _Tp>
struct __compatible_with : _Or< is_convertible<_Yp*, _Tp*>, __bounded_convertible_to_unbounded<_Yp, _Tp> > {};
#else
template <class _Yp, class _Tp>
struct __compatible_with : is_convertible<_Yp*, _Tp*> {};
#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>
struct __raw_pointer_compatible_with : _And< _Not<is_array<_Tp>>, is_convertible<_Yp*, _Tp*> > {};

template <class _Yp, class _Up, std::size_t _Np>
struct __raw_pointer_compatible_with<_Yp, _Up[_Np], __enable_if_t< is_convertible<_Yp (*)[_Np], _Up (*)[_Np]>::value> >
    : true_type {};

template <class _Yp, class _Up>
struct __raw_pointer_compatible_with<_Yp, _Up[], __enable_if_t< is_convertible<_Yp (*)[], _Up (*)[]>::value> >
    : true_type {};

#else
template <class _Yp, class _Tp>
struct __raw_pointer_compatible_with : is_convertible<_Yp*, _Tp*> {};
#endif // _LIBCPP_STD_VER >= 17

template <class _Ptr, class = void>
struct __is_deletable : false_type {};
template <class _Ptr>
struct __is_deletable<_Ptr, decltype(delete std::declval<_Ptr>())> : true_type {};

template <class _Ptr, class = void>
struct __is_array_deletable : false_type {};
template <class _Ptr>
struct __is_array_deletable<_Ptr, decltype(delete[] std::declval<_Ptr>())> : true_type {};

template <class _Dp, class _Pt, class = decltype(std::declval<_Dp>()(std::declval<_Pt>()))>
true_type __well_formed_deleter_test(int);

template <class, class>
false_type __well_formed_deleter_test(...);

template <class _Dp, class _Pt>
struct __well_formed_deleter : decltype(std::__well_formed_deleter_test<_Dp, _Pt>(0)) {};

template <class _Dp, class _Yp, class _Tp>
struct __shared_ptr_deleter_ctor_reqs {
  static const bool value = __raw_pointer_compatible_with<_Yp, _Tp>::value && is_move_constructible<_Dp>::value &&
                            __well_formed_deleter<_Dp, _Yp*>::value;
};

#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 _LIBCPP_TEMPLATE_VIS shared_ptr {
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

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,
            class = __enable_if_t< _And< __raw_pointer_compatible_with<_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) && !defined(_LIBCPP_COMPILER_GCC)
                                         ,
                                         _If<is_array<_Tp>::value, __is_array_deletable<_Yp*>, __is_deletable<_Yp*> >
#endif
                                         >::value > >
  _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, class = __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value> >
  _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d) : __ptr_(__p) {
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
    try {
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
      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);
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
    } catch (...) {
      __d(__p);
      throw;
    }
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
  }

  template <class _Yp,
            class _Dp,
            class _Alloc,
            class = __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value> >
  _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d, _Alloc __a) : __ptr_(__p) {
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
    try {
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
      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);
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
    } catch (...) {
      __d(__p);
      throw;
    }
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
  }

  template <class _Dp>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(nullptr_t __p, _Dp __d) : __ptr_(nullptr) {
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
    try {
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
      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
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
    } catch (...) {
      __d(__p);
      throw;
    }
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
  }

  template <class _Dp, class _Alloc>
  _LIBCPP_HIDE_FROM_ABI shared_ptr(nullptr_t __p, _Dp __d, _Alloc __a) : __ptr_(nullptr) {
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
    try {
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
      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());
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
    } catch (...) {
      __d(__p);
      throw;
    }
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
  }

  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, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
  _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, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
  _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, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
  _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)
      __throw_bad_weak_ptr();
  }

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

  template <class _Yp,
            class _Dp,
            class = __enable_if_t< !is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
                                   is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value > >
  _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
#if _LIBCPP_STD_VER >= 14
    if (__ptr_ == nullptr)
      __cntrl_ = nullptr;
    else
#endif
    {
      typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
      typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer, _Dp, _AllocT> _CntrlBlk;
      __cntrl_ = new _CntrlBlk(__r.get(), std::move(__r.get_deleter()), _AllocT());
      __enable_weak_this(__r.get(), __r.get());
    }
    __r.release();
  }

  template <class _Yp,
            class _Dp,
            class = void,
            class = __enable_if_t< is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
                                   is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value > >
  _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
#if _LIBCPP_STD_VER >= 14
    if (__ptr_ == nullptr)
      __cntrl_ = nullptr;
    else
#endif
    {
      typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
      typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer,
                                   reference_wrapper<__libcpp_remove_reference_t<_Dp> >,
                                   _AllocT>
          _CntrlBlk;
      __cntrl_ = new _CntrlBlk(__r.get(), std::ref(__r.get_deleter()), _AllocT());
      __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, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
  _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, class = __enable_if_t<__compatible_with<_Yp, _Tp>::value> >
  _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,
            class = __enable_if_t< !is_array<_Yp>::value &&
                                   is_convertible<_Yp*, typename shared_ptr<_Tp>::element_type*>::value > >
  _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,
      class = __enable_if_t<_And< __compatible_with<_Yp, _Tp>,
                                  is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*> >::value> >
  _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, class = __enable_if_t< __raw_pointer_compatible_with<_Yp, _Tp>::value > >
  _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p) {
    shared_ptr(__p).swap(*this);
  }

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

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

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

  _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_;
  }

  _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)
  _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>
  _LIBCPP_HIDE_FROM_ABI bool owner_before(shared_ptr<_Up> const& __p) const _NOEXCEPT {
    return __cntrl_ < __p.__cntrl_;
  }

  template <class _Up>
  _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
  _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

#ifndef _LIBCPP_HAS_NO_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_NO_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<_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,
            class = __enable_if_t< is_convertible<_OrigPtr*, const enable_shared_from_this<_Yp>*>::value > >
  _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)));
    }
  }

  _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(...) _NOEXCEPT {}

  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 _LIBCPP_TEMPLATE_VIS shared_ptr;
  template <class _Up>
  friend class _LIBCPP_TEMPLATE_VIS 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 _Tp, class _Alloc, class... _Args, class = __enable_if_t<!is_array<_Tp>::value> >
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, _Args&&... __args) {
  using _ControlBlock          = __shared_ptr_emplace<_Tp, _Alloc>;
  using _ControlBlockAllocator = typename __allocator_traits_rebind<_Alloc, _ControlBlock>::type;
  __allocation_guard<_ControlBlockAllocator> __guard(__a, 1);
  ::new ((void*)std::addressof(*__guard.__get())) _ControlBlock(__a, std::forward<_Args>(__args)...);
  auto __control_block = __guard.__release_ptr();
  return shared_ptr<_Tp>::__create_with_control_block(
      (*__control_block).__get_elem(), std::addressof(*__control_block));
}

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

#if _LIBCPP_STD_VER >= 20

template <class _Tp, class _Alloc, __enable_if_t<!is_array<_Tp>::value, int> = 0>
_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<_Tp>(__alloc);
}

template <class _Tp, __enable_if_t<!is_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
  return std::allocate_shared_for_overwrite<_Tp>(allocator<_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(_Tp);
    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(__libcpp_is_unbounded_array<_Array>::value);
  // 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(__libcpp_is_bounded_array<_Array>::value);
  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, class = __enable_if_t<is_bounded_array<_Tp>::value>>
_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, class = __enable_if_t<is_bounded_array<_Tp>::value>>
_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>
_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, class = __enable_if_t<is_bounded_array<_Tp>::value>>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared() {
  return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>());
}

template <class _Tp, class = __enable_if_t<is_bounded_array<_Tp>::value>>
_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>
_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, class = __enable_if_t<is_unbounded_array<_Tp>::value>>
_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, class = __enable_if_t<is_unbounded_array<_Tp>::value>>
_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>
_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, class = __enable_if_t<is_unbounded_array<_Tp>::value>>
_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, class = __enable_if_t<is_unbounded_array<_Tp>::value>>
_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>
_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<_Tp*>()(__x.get(), nullptr);
}

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool operator<(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
  return less<_Tp*>()(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>
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>
_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>
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>
_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>
_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>
_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>
_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>
_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

#ifndef _LIBCPP_HAS_NO_RTTI

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

#endif // _LIBCPP_HAS_NO_RTTI

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

private:
  element_type* __ptr_;
  __shared_weak_count* __cntrl_;

public:
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR weak_ptr() _NOEXCEPT;

  template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT;

  _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr const& __r) _NOEXCEPT;

  template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT;

  _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr&& __r) _NOEXCEPT;

  template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT;

  _LIBCPP_HIDE_FROM_ABI ~weak_ptr();

  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr const& __r) _NOEXCEPT;
  template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT;

  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr&& __r) _NOEXCEPT;
  template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT;

  template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT;

  _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr& __r) _NOEXCEPT;
  _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT;

  _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __cntrl_ ? __cntrl_->use_count() : 0; }
  _LIBCPP_HIDE_FROM_ABI bool expired() const _NOEXCEPT { return __cntrl_ == nullptr || __cntrl_->use_count() == 0; }
  _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> lock() const _NOEXCEPT;
  template <class _Up>
  _LIBCPP_HIDE_FROM_ABI bool owner_before(const shared_ptr<_Up>& __r) const _NOEXCEPT {
    return __cntrl_ < __r.__cntrl_;
  }
  template <class _Up>
  _LIBCPP_HIDE_FROM_ABI bool owner_before(const weak_ptr<_Up>& __r) const _NOEXCEPT {
    return __cntrl_ < __r.__cntrl_;
  }

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

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

template <class _Tp>
inline _LIBCPP_CONSTEXPR weak_ptr<_Tp>::weak_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}

template <class _Tp>
inline weak_ptr<_Tp>::weak_ptr(weak_ptr const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
  if (__cntrl_)
    __cntrl_->__add_weak();
}

template <class _Tp>
template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
inline weak_ptr<_Tp>::weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
  if (__cntrl_)
    __cntrl_->__add_weak();
}

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

template <class _Tp>
inline weak_ptr<_Tp>::weak_ptr(weak_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
  __r.__ptr_   = nullptr;
  __r.__cntrl_ = nullptr;
}

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

template <class _Tp>
weak_ptr<_Tp>::~weak_ptr() {
  if (__cntrl_)
    __cntrl_->__release_weak();
}

template <class _Tp>
inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr const& __r) _NOEXCEPT {
  weak_ptr(__r).swap(*this);
  return *this;
}

template <class _Tp>
template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT {
  weak_ptr(__r).swap(*this);
  return *this;
}

template <class _Tp>
inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr&& __r) _NOEXCEPT {
  weak_ptr(std::move(__r)).swap(*this);
  return *this;
}

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

template <class _Tp>
template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT {
  weak_ptr(__r).swap(*this);
  return *this;
}

template <class _Tp>
inline void weak_ptr<_Tp>::swap(weak_ptr& __r) _NOEXCEPT {
  std::swap(__ptr_, __r.__ptr_);
  std::swap(__cntrl_, __r.__cntrl_);
}

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

template <class _Tp>
inline void weak_ptr<_Tp>::reset() _NOEXCEPT {
  weak_ptr().swap(*this);
}

template <class _Tp>
shared_ptr<_Tp> weak_ptr<_Tp>::lock() const _NOEXCEPT {
  shared_ptr<_Tp> __r;
  __r.__cntrl_ = __cntrl_ ? __cntrl_->lock() : __cntrl_;
  if (__r.__cntrl_)
    __r.__ptr_ = __ptr_;
  return __r;
}

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

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS 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 _LIBCPP_TEMPLATE_VIS 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 _LIBCPP_TEMPLATE_VIS 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 _LIBCPP_TEMPLATE_VIS 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:
  _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> shared_from_this() { return shared_ptr<_Tp>(__weak_this_); }
  _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp const> shared_from_this() const { return shared_ptr<const _Tp>(__weak_this_); }

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

  _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 _LIBCPP_TEMPLATE_VIS hash;

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS 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

  _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 !defined(_LIBCPP_HAS_NO_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 // !defined(_LIBCPP_HAS_NO_THREADS)

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___MEMORY_SHARED_PTR_H