// shared_ptr and weak_ptr implementation details -*- C++ -*-
	
	// Copyright (C) 2007-2019 Free Software Foundation, Inc.
	//
	// This file is part of the GNU ISO C++ Library.  This library is free
	// software; you can redistribute it and/or modify it under the
	// terms of the GNU General Public License as published by the
	// Free Software Foundation; either version 3, or (at your option)
	// any later version.
	
	// This library is distributed in the hope that it will be useful,
	// but WITHOUT ANY WARRANTY; without even the implied warranty of
	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	// GNU General Public License for more details.
	
	// Under Section 7 of GPL version 3, you are granted additional
	// permissions described in the GCC Runtime Library Exception, version
	// 3.1, as published by the Free Software Foundation.
	
	// You should have received a copy of the GNU General Public License and
	// a copy of the GCC Runtime Library Exception along with this program;
	// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
	// <http://www.gnu.org/licenses/>.
	
	// GCC Note: Based on files from version 1.32.0 of the Boost library.
	
	//  shared_count.hpp
	//  Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
	
	//  shared_ptr.hpp
	//  Copyright (C) 1998, 1999 Greg Colvin and Beman Dawes.
	//  Copyright (C) 2001, 2002, 2003 Peter Dimov
	
	//  weak_ptr.hpp
	//  Copyright (C) 2001, 2002, 2003 Peter Dimov
	
	//  enable_shared_from_this.hpp
	//  Copyright (C) 2002 Peter Dimov
	
	// Distributed under the Boost Software License, Version 1.0. (See
	// accompanying file LICENSE_1_0.txt or copy at
	// http://www.boost.org/LICENSE_1_0.txt)
	
	/** @file bits/shared_ptr_base.h
	 *  This is an internal header file, included by other library headers.
	 *  Do not attempt to use it directly. @headername{memory}
	 */
	
	#ifndef _SHARED_PTR_BASE_H
	#define _SHARED_PTR_BASE_H 1
	
	#include <typeinfo>
	#include <bits/allocated_ptr.h>
	#include <bits/refwrap.h>
	#include <bits/stl_function.h>
	#include <ext/aligned_buffer.h>
	
	namespace std _GLIBCXX_VISIBILITY(default)
	{
	_GLIBCXX_BEGIN_NAMESPACE_VERSION
	
	#if _GLIBCXX_USE_DEPRECATED
	#pragma GCC diagnostic push
	#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
	  template<typename> class auto_ptr;
	#pragma GCC diagnostic pop
	#endif
	
	 /**
	   *  @brief  Exception possibly thrown by @c shared_ptr.
	   *  @ingroup exceptions
	   */
	  class bad_weak_ptr : public std::exception
	  {
	  public:
	    virtual char const* what() const noexcept;
	
	    virtual ~bad_weak_ptr() noexcept;
	  };
	
	  // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
	  inline void
	  __throw_bad_weak_ptr()
	  { _GLIBCXX_THROW_OR_ABORT(bad_weak_ptr()); }
	
	  using __gnu_cxx::_Lock_policy;
	  using __gnu_cxx::__default_lock_policy;
	  using __gnu_cxx::_S_single;
	  using __gnu_cxx::_S_mutex;
	  using __gnu_cxx::_S_atomic;
	
	  // Empty helper class except when the template argument is _S_mutex.
	  template<_Lock_policy _Lp>
	    class _Mutex_base
	    {
	    protected:
	      // The atomic policy uses fully-fenced builtins, single doesn't care.
	      enum { _S_need_barriers = 0 };
	    };
	
	  template<>
	    class _Mutex_base<_S_mutex>
	    : public __gnu_cxx::__mutex
	    {
	    protected:
	      // This policy is used when atomic builtins are not available.
	      // The replacement atomic operations might not have the necessary
	      // memory barriers.
	      enum { _S_need_barriers = 1 };
	    };
	
	  template<_Lock_policy _Lp = __default_lock_policy>
	    class _Sp_counted_base
	    : public _Mutex_base<_Lp>
	    {
	    public:
	      _Sp_counted_base() noexcept
	      : _M_use_count(1), _M_weak_count(1) { }
	
	      virtual
	      ~_Sp_counted_base() noexcept
	      { }
	
	      // Called when _M_use_count drops to zero, to release the resources
	      // managed by *this.
	      virtual void
	      _M_dispose() noexcept = 0;
	
	      // Called when _M_weak_count drops to zero.
	      virtual void
	      _M_destroy() noexcept
	      { delete this; }
	
	      virtual void*
	      _M_get_deleter(const std::type_info&) noexcept = 0;
	
	      void
	      _M_add_ref_copy()
	      { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
	
	      void
	      _M_add_ref_lock();
	
	      bool
	      _M_add_ref_lock_nothrow();
	
	      void
	      _M_release() noexcept
	      {
	        // Be race-detector-friendly.  For more info see bits/c++config.
	        _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_use_count);
		if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
		  {
	            _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_use_count);
		    _M_dispose();
		    // There must be a memory barrier between dispose() and destroy()
		    // to ensure that the effects of dispose() are observed in the
		    // thread that runs destroy().
		    // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
		    if (_Mutex_base<_Lp>::_S_need_barriers)
		      {
			__atomic_thread_fence (__ATOMIC_ACQ_REL);
		      }
	
	            // Be race-detector-friendly.  For more info see bits/c++config.
	            _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
		    if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
							       -1) == 1)
	              {
	                _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
		        _M_destroy();
	              }
		  }
	      }
	
	      void
	      _M_weak_add_ref() noexcept
	      { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
	
	      void
	      _M_weak_release() noexcept
	      {
	        // Be race-detector-friendly. For more info see bits/c++config.
	        _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
		if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
		  {
	            _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
		    if (_Mutex_base<_Lp>::_S_need_barriers)
		      {
		        // See _M_release(),
		        // destroy() must observe results of dispose()
			__atomic_thread_fence (__ATOMIC_ACQ_REL);
		      }
		    _M_destroy();
		  }
	      }
	
	      long
	      _M_get_use_count() const noexcept
	      {
	        // No memory barrier is used here so there is no synchronization
	        // with other threads.
	        return __atomic_load_n(&_M_use_count, __ATOMIC_RELAXED);
	      }
	
	    private:
	      _Sp_counted_base(_Sp_counted_base const&) = delete;
	      _Sp_counted_base& operator=(_Sp_counted_base const&) = delete;
	
	      _Atomic_word  _M_use_count;     // #shared
	      _Atomic_word  _M_weak_count;    // #weak + (#shared != 0)
	    };
	
	  template<>
	    inline void
	    _Sp_counted_base<_S_single>::
	    _M_add_ref_lock()
	    {
	      if (_M_use_count == 0)
		__throw_bad_weak_ptr();
	      ++_M_use_count;
	    }
	
	  template<>
	    inline void
	    _Sp_counted_base<_S_mutex>::
	    _M_add_ref_lock()
	    {
	      __gnu_cxx::__scoped_lock sentry(*this);
	      if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
		{
		  _M_use_count = 0;
		  __throw_bad_weak_ptr();
		}
	    }
	
	  template<>
	    inline void
	    _Sp_counted_base<_S_atomic>::
	    _M_add_ref_lock()
	    {
	      // Perform lock-free add-if-not-zero operation.
	      _Atomic_word __count = _M_get_use_count();
	      do
		{
		  if (__count == 0)
		    __throw_bad_weak_ptr();
		  // Replace the current counter value with the old value + 1, as
		  // long as it's not changed meanwhile.
		}
	      while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
						  true, __ATOMIC_ACQ_REL,
						  __ATOMIC_RELAXED));
	    }
	
	  template<>
	    inline bool
	    _Sp_counted_base<_S_single>::
	    _M_add_ref_lock_nothrow()
	    {
	      if (_M_use_count == 0)
		return false;
	      ++_M_use_count;
	      return true;
	    }
	
	  template<>
	    inline bool
	    _Sp_counted_base<_S_mutex>::
	    _M_add_ref_lock_nothrow()
	    {
	      __gnu_cxx::__scoped_lock sentry(*this);
	      if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
		{
		  _M_use_count = 0;
		  return false;
		}
	      return true;
	    }
	
	  template<>
	    inline bool
	    _Sp_counted_base<_S_atomic>::
	    _M_add_ref_lock_nothrow()
	    {
	      // Perform lock-free add-if-not-zero operation.
	      _Atomic_word __count = _M_get_use_count();
	      do
		{
		  if (__count == 0)
		    return false;
		  // Replace the current counter value with the old value + 1, as
		  // long as it's not changed meanwhile.
		}
	      while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
						  true, __ATOMIC_ACQ_REL,
						  __ATOMIC_RELAXED));
	      return true;
	    }
	
	  template<>
	    inline void
	    _Sp_counted_base<_S_single>::_M_add_ref_copy()
	    { ++_M_use_count; }
	
	  template<>
	    inline void
	    _Sp_counted_base<_S_single>::_M_release() noexcept
	    {
	      if (--_M_use_count == 0)
	        {
	          _M_dispose();
	          if (--_M_weak_count == 0)
	            _M_destroy();
	        }
	    }
	
	  template<>
	    inline void
	    _Sp_counted_base<_S_single>::_M_weak_add_ref() noexcept
	    { ++_M_weak_count; }
	
	  template<>
	    inline void
	    _Sp_counted_base<_S_single>::_M_weak_release() noexcept
	    {
	      if (--_M_weak_count == 0)
	        _M_destroy();
	    }
	
	  template<>
	    inline long
	    _Sp_counted_base<_S_single>::_M_get_use_count() const noexcept
	    { return _M_use_count; }
	
	
	  // Forward declarations.
	  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
	    class __shared_ptr;
	
	  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
	    class __weak_ptr;
	
	  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
	    class __enable_shared_from_this;
	
	  template<typename _Tp>
	    class shared_ptr;
	
	  template<typename _Tp>
	    class weak_ptr;
	
	  template<typename _Tp>
	    struct owner_less;
	
	  template<typename _Tp>
	    class enable_shared_from_this;
	
	  template<_Lock_policy _Lp = __default_lock_policy>
	    class __weak_count;
	
	  template<_Lock_policy _Lp = __default_lock_policy>
	    class __shared_count;
	
	
	  // Counted ptr with no deleter or allocator support
	  template<typename _Ptr, _Lock_policy _Lp>
	    class _Sp_counted_ptr final : public _Sp_counted_base<_Lp>
	    {
	    public:
	      explicit
	      _Sp_counted_ptr(_Ptr __p) noexcept
	      : _M_ptr(__p) { }
	
	      virtual void
	      _M_dispose() noexcept
	      { delete _M_ptr; }
	
	      virtual void
	      _M_destroy() noexcept
	      { delete this; }
	
	      virtual void*
	      _M_get_deleter(const std::type_info&) noexcept
	      { return nullptr; }
	
	      _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
	      _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
	
	    private:
	      _Ptr             _M_ptr;
	    };
	
	  template<>
	    inline void
	    _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() noexcept { }
	
	  template<>
	    inline void
	    _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() noexcept { }
	
	  template<>
	    inline void
	    _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
	
	  template<int _Nm, typename _Tp,
		   bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>
	    struct _Sp_ebo_helper;
	
	  /// Specialization using EBO.
	  template<int _Nm, typename _Tp>
	    struct _Sp_ebo_helper<_Nm, _Tp, true> : private _Tp
	    {
	      explicit _Sp_ebo_helper(const _Tp& __tp) : _Tp(__tp) { }
	      explicit _Sp_ebo_helper(_Tp&& __tp) : _Tp(std::move(__tp)) { }
	
	      static _Tp&
	      _S_get(_Sp_ebo_helper& __eboh) { return static_cast<_Tp&>(__eboh); }
	    };
	
	  /// Specialization not using EBO.
	  template<int _Nm, typename _Tp>
	    struct _Sp_ebo_helper<_Nm, _Tp, false>
	    {
	      explicit _Sp_ebo_helper(const _Tp& __tp) : _M_tp(__tp) { }
	      explicit _Sp_ebo_helper(_Tp&& __tp) : _M_tp(std::move(__tp)) { }
	
	      static _Tp&
	      _S_get(_Sp_ebo_helper& __eboh)
	      { return __eboh._M_tp; }
	
	    private:
	      _Tp _M_tp;
	    };
	
	  // Support for custom deleter and/or allocator
	  template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
	    class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>
	    {
	      class _Impl : _Sp_ebo_helper<0, _Deleter>, _Sp_ebo_helper<1, _Alloc>
	      {
		typedef _Sp_ebo_helper<0, _Deleter>	_Del_base;
		typedef _Sp_ebo_helper<1, _Alloc>	_Alloc_base;
	
	      public:
		_Impl(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept
		: _M_ptr(__p), _Del_base(std::move(__d)), _Alloc_base(__a)
		{ }
	
		_Deleter& _M_del() noexcept { return _Del_base::_S_get(*this); }
		_Alloc& _M_alloc() noexcept { return _Alloc_base::_S_get(*this); }
	
		_Ptr _M_ptr;
	      };
	
	    public:
	      using __allocator_type = __alloc_rebind<_Alloc, _Sp_counted_deleter>;
	
	      // __d(__p) must not throw.
	      _Sp_counted_deleter(_Ptr __p, _Deleter __d) noexcept
	      : _M_impl(__p, std::move(__d), _Alloc()) { }
	
	      // __d(__p) must not throw.
	      _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept
	      : _M_impl(__p, std::move(__d), __a) { }
	
	      ~_Sp_counted_deleter() noexcept { }
	
	      virtual void
	      _M_dispose() noexcept
	      { _M_impl._M_del()(_M_impl._M_ptr); }
	
	      virtual void
	      _M_destroy() noexcept
	      {
		__allocator_type __a(_M_impl._M_alloc());
		__allocated_ptr<__allocator_type> __guard_ptr{ __a, this };
		this->~_Sp_counted_deleter();
	      }
	
	      virtual void*
	      _M_get_deleter(const std::type_info& __ti) noexcept
	      {
	#if __cpp_rtti
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 2400. shared_ptr's get_deleter() should use addressof()
	        return __ti == typeid(_Deleter)
		  ? std::__addressof(_M_impl._M_del())
		  : nullptr;
	#else
	        return nullptr;
	#endif
	      }
	
	    private:
	      _Impl _M_impl;
	    };
	
	  // helpers for make_shared / allocate_shared
	
	  struct _Sp_make_shared_tag
	  {
	  private:
	    template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
	      friend class _Sp_counted_ptr_inplace;
	
	    static const type_info&
	    _S_ti() noexcept _GLIBCXX_VISIBILITY(default)
	    {
	      alignas(type_info) static constexpr char __tag[sizeof(type_info)] = { };
	      return reinterpret_cast<const type_info&>(__tag);
	    }
	
	    static bool _S_eq(const type_info&) noexcept;
	  };
	
	  template<typename _Alloc>
	    struct _Sp_alloc_shared_tag
	    {
	      const _Alloc& _M_a;
	    };
	
	  template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
	    class _Sp_counted_ptr_inplace final : public _Sp_counted_base<_Lp>
	    {
	      class _Impl : _Sp_ebo_helper<0, _Alloc>
	      {
		typedef _Sp_ebo_helper<0, _Alloc>	_A_base;
	
	      public:
		explicit _Impl(_Alloc __a) noexcept : _A_base(__a) { }
	
		_Alloc& _M_alloc() noexcept { return _A_base::_S_get(*this); }
	
		__gnu_cxx::__aligned_buffer<_Tp> _M_storage;
	      };
	
	    public:
	      using __allocator_type = __alloc_rebind<_Alloc, _Sp_counted_ptr_inplace>;
	
	      // Alloc parameter is not a reference so doesn't alias anything in __args
	      template<typename... _Args>
		_Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
		: _M_impl(__a)
		{
		  // _GLIBCXX_RESOLVE_LIB_DEFECTS
		  // 2070.  allocate_shared should use allocator_traits<A>::construct
		  allocator_traits<_Alloc>::construct(__a, _M_ptr(),
		      std::forward<_Args>(__args)...); // might throw
		}
	
	      ~_Sp_counted_ptr_inplace() noexcept { }
	
	      virtual void
	      _M_dispose() noexcept
	      {
		allocator_traits<_Alloc>::destroy(_M_impl._M_alloc(), _M_ptr());
	      }
	
	      // Override because the allocator needs to know the dynamic type
	      virtual void
	      _M_destroy() noexcept
	      {
		__allocator_type __a(_M_impl._M_alloc());
		__allocated_ptr<__allocator_type> __guard_ptr{ __a, this };
		this->~_Sp_counted_ptr_inplace();
	      }
	
	    private:
	      friend class __shared_count<_Lp>; // To be able to call _M_ptr().
	
	      // No longer used, but code compiled against old libstdc++ headers
	      // might still call it from __shared_ptr ctor to get the pointer out.
	      virtual void*
	      _M_get_deleter(const std::type_info& __ti) noexcept override
	      {
		auto __ptr = const_cast<typename remove_cv<_Tp>::type*>(_M_ptr());
		// Check for the fake type_info first, so we don't try to access it
		// as a real type_info object. Otherwise, check if it's the real
		// type_info for this class. With RTTI enabled we can check directly,
		// or call a library function to do it.
		if (&__ti == &_Sp_make_shared_tag::_S_ti()
		    ||
	#if __cpp_rtti
		    __ti == typeid(_Sp_make_shared_tag)
	#else
		    _Sp_make_shared_tag::_S_eq(__ti)
	#endif
		   )
		  return __ptr;
		return nullptr;
	      }
	
	      _Tp* _M_ptr() noexcept { return _M_impl._M_storage._M_ptr(); }
	
	      _Impl _M_impl;
	    };
	
	  // The default deleter for shared_ptr<T[]> and shared_ptr<T[N]>.
	  struct __sp_array_delete
	  {
	    template<typename _Yp>
	      void operator()(_Yp* __p) const { delete[] __p; }
	  };
	
	  template<_Lock_policy _Lp>
	    class __shared_count
	    {
	      template<typename _Tp>
		struct __not_alloc_shared_tag { using type = void; };
	
	      template<typename _Tp>
		struct __not_alloc_shared_tag<_Sp_alloc_shared_tag<_Tp>> { };
	
	    public:
	      constexpr __shared_count() noexcept : _M_pi(0)
	      { }
	
	      template<typename _Ptr>
	        explicit
		__shared_count(_Ptr __p) : _M_pi(0)
		{
		  __try
		    {
		      _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
		    }
		  __catch(...)
		    {
		      delete __p;
		      __throw_exception_again;
		    }
		}
	
	      template<typename _Ptr>
		__shared_count(_Ptr __p, /* is_array = */ false_type)
		: __shared_count(__p)
		{ }
	
	      template<typename _Ptr>
		__shared_count(_Ptr __p, /* is_array = */ true_type)
		: __shared_count(__p, __sp_array_delete{}, allocator<void>())
		{ }
	
	      template<typename _Ptr, typename _Deleter,
		       typename = typename __not_alloc_shared_tag<_Deleter>::type>
		__shared_count(_Ptr __p, _Deleter __d)
		: __shared_count(__p, std::move(__d), allocator<void>())
		{ }
	
	      template<typename _Ptr, typename _Deleter, typename _Alloc,
		       typename = typename __not_alloc_shared_tag<_Deleter>::type>
		__shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
		{
		  typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
		  __try
		    {
		      typename _Sp_cd_type::__allocator_type __a2(__a);
		      auto __guard = std::__allocate_guarded(__a2);
		      _Sp_cd_type* __mem = __guard.get();
		      ::new (__mem) _Sp_cd_type(__p, std::move(__d), std::move(__a));
		      _M_pi = __mem;
		      __guard = nullptr;
		    }
		  __catch(...)
		    {
		      __d(__p); // Call _Deleter on __p.
		      __throw_exception_again;
		    }
		}
	
	      template<typename _Tp, typename _Alloc, typename... _Args>
		__shared_count(_Tp*& __p, _Sp_alloc_shared_tag<_Alloc> __a,
			       _Args&&... __args)
		{
		  typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
		  typename _Sp_cp_type::__allocator_type __a2(__a._M_a);
		  auto __guard = std::__allocate_guarded(__a2);
		  _Sp_cp_type* __mem = __guard.get();
		  auto __pi = ::new (__mem)
		    _Sp_cp_type(__a._M_a, std::forward<_Args>(__args)...);
		  __guard = nullptr;
		  _M_pi = __pi;
		  __p = __pi->_M_ptr();
		}
	
	#if _GLIBCXX_USE_DEPRECATED
	#pragma GCC diagnostic push
	#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
	      // Special case for auto_ptr<_Tp> to provide the strong guarantee.
	      template<typename _Tp>
	        explicit
		__shared_count(std::auto_ptr<_Tp>&& __r);
	#pragma GCC diagnostic pop
	#endif
	
	      // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
	      template<typename _Tp, typename _Del>
	        explicit
		__shared_count(std::unique_ptr<_Tp, _Del>&& __r) : _M_pi(0)
		{
		  // _GLIBCXX_RESOLVE_LIB_DEFECTS
		  // 2415. Inconsistency between unique_ptr and shared_ptr
		  if (__r.get() == nullptr)
		    return;
	
		  using _Ptr = typename unique_ptr<_Tp, _Del>::pointer;
		  using _Del2 = typename conditional<is_reference<_Del>::value,
		      reference_wrapper<typename remove_reference<_Del>::type>,
		      _Del>::type;
		  using _Sp_cd_type
		    = _Sp_counted_deleter<_Ptr, _Del2, allocator<void>, _Lp>;
		  using _Alloc = allocator<_Sp_cd_type>;
		  using _Alloc_traits = allocator_traits<_Alloc>;
		  _Alloc __a;
		  _Sp_cd_type* __mem = _Alloc_traits::allocate(__a, 1);
		  _Alloc_traits::construct(__a, __mem, __r.release(),
					   __r.get_deleter());  // non-throwing
		  _M_pi = __mem;
		}
	
	      // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
	      explicit __shared_count(const __weak_count<_Lp>& __r);
	
	      // Does not throw if __r._M_get_use_count() == 0, caller must check.
	      explicit __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t);
	
	      ~__shared_count() noexcept
	      {
		if (_M_pi != nullptr)
		  _M_pi->_M_release();
	      }
	
	      __shared_count(const __shared_count& __r) noexcept
	      : _M_pi(__r._M_pi)
	      {
		if (_M_pi != 0)
		  _M_pi->_M_add_ref_copy();
	      }
	
	      __shared_count&
	      operator=(const __shared_count& __r) noexcept
	      {
		_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
		if (__tmp != _M_pi)
		  {
		    if (__tmp != 0)
		      __tmp->_M_add_ref_copy();
		    if (_M_pi != 0)
		      _M_pi->_M_release();
		    _M_pi = __tmp;
		  }
		return *this;
	      }
	
	      void
	      _M_swap(__shared_count& __r) noexcept
	      {
		_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
		__r._M_pi = _M_pi;
		_M_pi = __tmp;
	      }
	
	      long
	      _M_get_use_count() const noexcept
	      { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
	
	      bool
	      _M_unique() const noexcept
	      { return this->_M_get_use_count() == 1; }
	
	      void*
	      _M_get_deleter(const std::type_info& __ti) const noexcept
	      { return _M_pi ? _M_pi->_M_get_deleter(__ti) : nullptr; }
	
	      bool
	      _M_less(const __shared_count& __rhs) const noexcept
	      { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
	
	      bool
	      _M_less(const __weak_count<_Lp>& __rhs) const noexcept
	      { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
	
	      // Friend function injected into enclosing namespace and found by ADL
	      friend inline bool
	      operator==(const __shared_count& __a, const __shared_count& __b) noexcept
	      { return __a._M_pi == __b._M_pi; }
	
	    private:
	      friend class __weak_count<_Lp>;
	
	      _Sp_counted_base<_Lp>*  _M_pi;
	    };
	
	
	  template<_Lock_policy _Lp>
	    class __weak_count
	    {
	    public:
	      constexpr __weak_count() noexcept : _M_pi(nullptr)
	      { }
	
	      __weak_count(const __shared_count<_Lp>& __r) noexcept
	      : _M_pi(__r._M_pi)
	      {
		if (_M_pi != nullptr)
		  _M_pi->_M_weak_add_ref();
	      }
	
	      __weak_count(const __weak_count& __r) noexcept
	      : _M_pi(__r._M_pi)
	      {
		if (_M_pi != nullptr)
		  _M_pi->_M_weak_add_ref();
	      }
	
	      __weak_count(__weak_count&& __r) noexcept
	      : _M_pi(__r._M_pi)
	      { __r._M_pi = nullptr; }
	
	      ~__weak_count() noexcept
	      {
		if (_M_pi != nullptr)
		  _M_pi->_M_weak_release();
	      }
	
	      __weak_count&
	      operator=(const __shared_count<_Lp>& __r) noexcept
	      {
		_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
		if (__tmp != nullptr)
		  __tmp->_M_weak_add_ref();
		if (_M_pi != nullptr)
		  _M_pi->_M_weak_release();
		_M_pi = __tmp;
		return *this;
	      }
	
	      __weak_count&
	      operator=(const __weak_count& __r) noexcept
	      {
		_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
		if (__tmp != nullptr)
		  __tmp->_M_weak_add_ref();
		if (_M_pi != nullptr)
		  _M_pi->_M_weak_release();
		_M_pi = __tmp;
		return *this;
	      }
	
	      __weak_count&
	      operator=(__weak_count&& __r) noexcept
	      {
		if (_M_pi != nullptr)
		  _M_pi->_M_weak_release();
		_M_pi = __r._M_pi;
	        __r._M_pi = nullptr;
		return *this;
	      }
	
	      void
	      _M_swap(__weak_count& __r) noexcept
	      {
		_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
		__r._M_pi = _M_pi;
		_M_pi = __tmp;
	      }
	
	      long
	      _M_get_use_count() const noexcept
	      { return _M_pi != nullptr ? _M_pi->_M_get_use_count() : 0; }
	
	      bool
	      _M_less(const __weak_count& __rhs) const noexcept
	      { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
	
	      bool
	      _M_less(const __shared_count<_Lp>& __rhs) const noexcept
	      { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
	
	      // Friend function injected into enclosing namespace and found by ADL
	      friend inline bool
	      operator==(const __weak_count& __a, const __weak_count& __b) noexcept
	      { return __a._M_pi == __b._M_pi; }
	
	    private:
	      friend class __shared_count<_Lp>;
	
	      _Sp_counted_base<_Lp>*  _M_pi;
	    };
	
	  // Now that __weak_count is defined we can define this constructor:
	  template<_Lock_policy _Lp>
	    inline
	    __shared_count<_Lp>::__shared_count(const __weak_count<_Lp>& __r)
	    : _M_pi(__r._M_pi)
	    {
	      if (_M_pi != nullptr)
		_M_pi->_M_add_ref_lock();
	      else
		__throw_bad_weak_ptr();
	    }
	
	  // Now that __weak_count is defined we can define this constructor:
	  template<_Lock_policy _Lp>
	    inline
	    __shared_count<_Lp>::
	    __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t)
	    : _M_pi(__r._M_pi)
	    {
	      if (_M_pi != nullptr)
		if (!_M_pi->_M_add_ref_lock_nothrow())
		  _M_pi = nullptr;
	    }
	
	#define __cpp_lib_shared_ptr_arrays 201611L
	
	  // Helper traits for shared_ptr of array:
	
	  // 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 U cv [].
	  template<typename _Yp_ptr, typename _Tp_ptr>
	    struct __sp_compatible_with
	    : false_type
	    { };
	
	  template<typename _Yp, typename _Tp>
	    struct __sp_compatible_with<_Yp*, _Tp*>
	    : is_convertible<_Yp*, _Tp*>::type
	    { };
	
	  template<typename _Up, size_t _Nm>
	    struct __sp_compatible_with<_Up(*)[_Nm], _Up(*)[]>
	    : true_type
	    { };
	
	  template<typename _Up, size_t _Nm>
	    struct __sp_compatible_with<_Up(*)[_Nm], const _Up(*)[]>
	    : true_type
	    { };
	
	  template<typename _Up, size_t _Nm>
	    struct __sp_compatible_with<_Up(*)[_Nm], volatile _Up(*)[]>
	    : true_type
	    { };
	
	  template<typename _Up, size_t _Nm>
	    struct __sp_compatible_with<_Up(*)[_Nm], const volatile _Up(*)[]>
	    : true_type
	    { };
	
	  // Test conversion from Y(*)[N] to U(*)[N] without forming invalid type Y[N].
	  template<typename _Up, size_t _Nm, typename _Yp, typename = void>
	    struct __sp_is_constructible_arrN
	    : false_type
	    { };
	
	  template<typename _Up, size_t _Nm, typename _Yp>
	    struct __sp_is_constructible_arrN<_Up, _Nm, _Yp, __void_t<_Yp[_Nm]>>
	    : is_convertible<_Yp(*)[_Nm], _Up(*)[_Nm]>::type
	    { };
	
	  // Test conversion from Y(*)[] to U(*)[] without forming invalid type Y[].
	  template<typename _Up, typename _Yp, typename = void>
	    struct __sp_is_constructible_arr
	    : false_type
	    { };
	
	  template<typename _Up, typename _Yp>
	    struct __sp_is_constructible_arr<_Up, _Yp, __void_t<_Yp[]>>
	    : is_convertible<_Yp(*)[], _Up(*)[]>::type
	    { };
	
	  // Trait to check if shared_ptr<T> can be constructed from Y*.
	  template<typename _Tp, typename _Yp>
	    struct __sp_is_constructible;
	
	  // When T is U[N], Y(*)[N] shall be convertible to T*;
	  template<typename _Up, size_t _Nm, typename _Yp>
	    struct __sp_is_constructible<_Up[_Nm], _Yp>
	    : __sp_is_constructible_arrN<_Up, _Nm, _Yp>::type
	    { };
	
	  // when T is U[], Y(*)[] shall be convertible to T*;
	  template<typename _Up, typename _Yp>
	    struct __sp_is_constructible<_Up[], _Yp>
	    : __sp_is_constructible_arr<_Up, _Yp>::type
	    { };
	
	  // otherwise, Y* shall be convertible to T*.
	  template<typename _Tp, typename _Yp>
	    struct __sp_is_constructible
	    : is_convertible<_Yp*, _Tp*>::type
	    { };
	
	
	  // Define operator* and operator-> for shared_ptr<T>.
	  template<typename _Tp, _Lock_policy _Lp,
		   bool = is_array<_Tp>::value, bool = is_void<_Tp>::value>
	    class __shared_ptr_access
	    {
	    public:
	      using element_type = _Tp;
	
	      element_type&
	      operator*() const noexcept
	      {
		__glibcxx_assert(_M_get() != nullptr);
		return *_M_get();
	      }
	
	      element_type*
	      operator->() const noexcept
	      {
		_GLIBCXX_DEBUG_PEDASSERT(_M_get() != nullptr);
		return _M_get();
	      }
	
	    private:
	      element_type*
	      _M_get() const noexcept
	      { return static_cast<const __shared_ptr<_Tp, _Lp>*>(this)->get(); }
	    };
	
	  // Define operator-> for shared_ptr<cv void>.
	  template<typename _Tp, _Lock_policy _Lp>
	    class __shared_ptr_access<_Tp, _Lp, false, true>
	    {
	    public:
	      using element_type = _Tp;
	
	      element_type*
	      operator->() const noexcept
	      {
		auto __ptr = static_cast<const __shared_ptr<_Tp, _Lp>*>(this)->get();
		_GLIBCXX_DEBUG_PEDASSERT(__ptr != nullptr);
		return __ptr;
	      }
	    };
	
	  // Define operator[] for shared_ptr<T[]> and shared_ptr<T[N]>.
	  template<typename _Tp, _Lock_policy _Lp>
	    class __shared_ptr_access<_Tp, _Lp, true, false>
	    {
	    public:
	      using element_type = typename remove_extent<_Tp>::type;
	
	#if __cplusplus <= 201402L
	      [[__deprecated__("shared_ptr<T[]>::operator* is absent from C++17")]]
	      element_type&
	      operator*() const noexcept
	      {
		__glibcxx_assert(_M_get() != nullptr);
		return *_M_get();
	      }
	
	      [[__deprecated__("shared_ptr<T[]>::operator-> is absent from C++17")]]
	      element_type*
	      operator->() const noexcept
	      {
		_GLIBCXX_DEBUG_PEDASSERT(_M_get() != nullptr);
		return _M_get();
	      }
	#endif
	
	      element_type&
	      operator[](ptrdiff_t __i) const
	      {
		__glibcxx_assert(_M_get() != nullptr);
		__glibcxx_assert(!extent<_Tp>::value || __i < extent<_Tp>::value);
		return _M_get()[__i];
	      }
	
	    private:
	      element_type*
	      _M_get() const noexcept
	      { return static_cast<const __shared_ptr<_Tp, _Lp>*>(this)->get(); }
	    };
	
	  template<typename _Tp, _Lock_policy _Lp>
	    class __shared_ptr
	    : public __shared_ptr_access<_Tp, _Lp>
	    {
	    public:
	      using element_type = typename remove_extent<_Tp>::type;
	
	    private:
	      // Constraint for taking ownership of a pointer of type _Yp*:
	      template<typename _Yp>
		using _SafeConv
		  = typename enable_if<__sp_is_constructible<_Tp, _Yp>::value>::type;
	
	      // Constraint for construction from shared_ptr and weak_ptr:
	      template<typename _Yp, typename _Res = void>
		using _Compatible = typename
		  enable_if<__sp_compatible_with<_Yp*, _Tp*>::value, _Res>::type;
	
	      // Constraint for assignment from shared_ptr and weak_ptr:
	      template<typename _Yp>
		using _Assignable = _Compatible<_Yp, __shared_ptr&>;
	
	      // Constraint for construction from unique_ptr:
	      template<typename _Yp, typename _Del, typename _Res = void,
		       typename _Ptr = typename unique_ptr<_Yp, _Del>::pointer>
		using _UniqCompatible = typename enable_if<__and_<
		  __sp_compatible_with<_Yp*, _Tp*>, is_convertible<_Ptr, element_type*>
		  >::value, _Res>::type;
	
	      // Constraint for assignment from unique_ptr:
	      template<typename _Yp, typename _Del>
		using _UniqAssignable = _UniqCompatible<_Yp, _Del, __shared_ptr&>;
	
	    public:
	
	#if __cplusplus > 201402L
	      using weak_type = __weak_ptr<_Tp, _Lp>;
	#endif
	
	      constexpr __shared_ptr() noexcept
	      : _M_ptr(0), _M_refcount()
	      { }
	
	      template<typename _Yp, typename = _SafeConv<_Yp>>
		explicit
		__shared_ptr(_Yp* __p)
		: _M_ptr(__p), _M_refcount(__p, typename is_array<_Tp>::type())
		{
		  static_assert( !is_void<_Yp>::value, "incomplete type" );
		  static_assert( sizeof(_Yp) > 0, "incomplete type" );
		  _M_enable_shared_from_this_with(__p);
		}
	
	      template<typename _Yp, typename _Deleter, typename = _SafeConv<_Yp>>
		__shared_ptr(_Yp* __p, _Deleter __d)
		: _M_ptr(__p), _M_refcount(__p, std::move(__d))
		{
		  static_assert(__is_invocable<_Deleter&, _Yp*&>::value,
		      "deleter expression d(p) is well-formed");
		  _M_enable_shared_from_this_with(__p);
		}
	
	      template<typename _Yp, typename _Deleter, typename _Alloc,
		       typename = _SafeConv<_Yp>>
		__shared_ptr(_Yp* __p, _Deleter __d, _Alloc __a)
		: _M_ptr(__p), _M_refcount(__p, std::move(__d), std::move(__a))
		{
		  static_assert(__is_invocable<_Deleter&, _Yp*&>::value,
		      "deleter expression d(p) is well-formed");
		  _M_enable_shared_from_this_with(__p);
		}
	
	      template<typename _Deleter>
		__shared_ptr(nullptr_t __p, _Deleter __d)
		: _M_ptr(0), _M_refcount(__p, std::move(__d))
		{ }
	
	      template<typename _Deleter, typename _Alloc>
	        __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
		: _M_ptr(0), _M_refcount(__p, std::move(__d), std::move(__a))
		{ }
	
	      template<typename _Yp>
		__shared_ptr(const __shared_ptr<_Yp, _Lp>& __r,
			     element_type* __p) noexcept
		: _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
		{ }
	
	      __shared_ptr(const __shared_ptr&) noexcept = default;

	      __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
	      ~__shared_ptr() = default;
	
	      template<typename _Yp, typename = _Compatible<_Yp>>
		__shared_ptr(const __shared_ptr<_Yp, _Lp>& __r) noexcept
		: _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
		{ }
	
	      __shared_ptr(__shared_ptr&& __r) noexcept
	      : _M_ptr(__r._M_ptr), _M_refcount()
	      {
		_M_refcount._M_swap(__r._M_refcount);
		__r._M_ptr = 0;
	      }
	
	      template<typename _Yp, typename = _Compatible<_Yp>>
		__shared_ptr(__shared_ptr<_Yp, _Lp>&& __r) noexcept
		: _M_ptr(__r._M_ptr), _M_refcount()
		{
		  _M_refcount._M_swap(__r._M_refcount);
		  __r._M_ptr = 0;
		}
	
	      template<typename _Yp, typename = _Compatible<_Yp>>
		explicit __shared_ptr(const __weak_ptr<_Yp, _Lp>& __r)
		: _M_refcount(__r._M_refcount) // may throw
		{
		  // It is now safe to copy __r._M_ptr, as
		  // _M_refcount(__r._M_refcount) did not throw.
		  _M_ptr = __r._M_ptr;
		}
	
	      // If an exception is thrown this constructor has no effect.
	      template<typename _Yp, typename _Del,
		       typename = _UniqCompatible<_Yp, _Del>>
		__shared_ptr(unique_ptr<_Yp, _Del>&& __r)
		: _M_ptr(__r.get()), _M_refcount()
		{
		  auto __raw = __to_address(__r.get());
		  _M_refcount = __shared_count<_Lp>(std::move(__r));
		  _M_enable_shared_from_this_with(__raw);
		}
	
	#if __cplusplus <= 201402L && _GLIBCXX_USE_DEPRECATED
	    protected:
	      // If an exception is thrown this constructor has no effect.
	      template<typename _Tp1, typename _Del,
		       typename enable_if<__and_<
			 __not_<is_array<_Tp>>, is_array<_Tp1>,
		         is_convertible<typename unique_ptr<_Tp1, _Del>::pointer, _Tp*>
		       >::value, bool>::type = true>
		__shared_ptr(unique_ptr<_Tp1, _Del>&& __r, __sp_array_delete)
		: _M_ptr(__r.get()), _M_refcount()
		{
		  auto __raw = __to_address(__r.get());
		  _M_refcount = __shared_count<_Lp>(std::move(__r));
		  _M_enable_shared_from_this_with(__raw);
		}
	    public:
	#endif
	
	#if _GLIBCXX_USE_DEPRECATED
	#pragma GCC diagnostic push
	#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
	      // Postcondition: use_count() == 1 and __r.get() == 0
	      template<typename _Yp, typename = _Compatible<_Yp>>
		__shared_ptr(auto_ptr<_Yp>&& __r);
	#pragma GCC diagnostic pop
	#endif
	
	      constexpr __shared_ptr(nullptr_t) noexcept : __shared_ptr() { }
	
	      template<typename _Yp>
		_Assignable<_Yp>
		operator=(const __shared_ptr<_Yp, _Lp>& __r) noexcept
		{
		  _M_ptr = __r._M_ptr;
		  _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
		  return *this;
		}
	
	#if _GLIBCXX_USE_DEPRECATED
	#pragma GCC diagnostic push
	#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
	      template<typename _Yp>
		_Assignable<_Yp>
		operator=(auto_ptr<_Yp>&& __r)
		{
		  __shared_ptr(std::move(__r)).swap(*this);
		  return *this;
		}
	#pragma GCC diagnostic pop
	#endif
	
	      __shared_ptr&
	      operator=(__shared_ptr&& __r) noexcept
	      {
		__shared_ptr(std::move(__r)).swap(*this);
		return *this;
	      }
	
	      template<class _Yp>
		_Assignable<_Yp>
		operator=(__shared_ptr<_Yp, _Lp>&& __r) noexcept
		{
		  __shared_ptr(std::move(__r)).swap(*this);
		  return *this;
		}
	
	      template<typename _Yp, typename _Del>
		_UniqAssignable<_Yp, _Del>
		operator=(unique_ptr<_Yp, _Del>&& __r)
		{
		  __shared_ptr(std::move(__r)).swap(*this);
		  return *this;
		}
	
	      void
	      reset() noexcept
	      { __shared_ptr().swap(*this); }
	
	      template<typename _Yp>
		_SafeConv<_Yp>
		reset(_Yp* __p) // _Yp must be complete.
		{
		  // Catch self-reset errors.
		  __glibcxx_assert(__p == 0 || __p != _M_ptr);
		  __shared_ptr(__p).swap(*this);
		}
	
	      template<typename _Yp, typename _Deleter>
		_SafeConv<_Yp>
		reset(_Yp* __p, _Deleter __d)
		{ __shared_ptr(__p, std::move(__d)).swap(*this); }
	
	      template<typename _Yp, typename _Deleter, typename _Alloc>
		_SafeConv<_Yp>
		reset(_Yp* __p, _Deleter __d, _Alloc __a)
	        { __shared_ptr(__p, std::move(__d), std::move(__a)).swap(*this); }
	
	      element_type*
	      get() const noexcept
	      { return _M_ptr; }
	
	      explicit operator bool() const // never throws
	      { return _M_ptr == 0 ? false : true; }
	
	      bool
	      unique() const noexcept
	      { return _M_refcount._M_unique(); }
	
	      long
	      use_count() const noexcept
	      { return _M_refcount._M_get_use_count(); }
	
	      void
	      swap(__shared_ptr<_Tp, _Lp>& __other) noexcept
	      {
		std::swap(_M_ptr, __other._M_ptr);
		_M_refcount._M_swap(__other._M_refcount);
	      }
	
	      template<typename _Tp1>
		bool
		owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const noexcept
		{ return _M_refcount._M_less(__rhs._M_refcount); }
	
	      template<typename _Tp1>
		bool
		owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const noexcept
		{ return _M_refcount._M_less(__rhs._M_refcount); }
	
	    protected:
	      // This constructor is non-standard, it is used by allocate_shared.
	      template<typename _Alloc, typename... _Args>
		__shared_ptr(_Sp_alloc_shared_tag<_Alloc> __tag, _Args&&... __args)
		: _M_ptr(), _M_refcount(_M_ptr, __tag, std::forward<_Args>(__args)...)
		{ _M_enable_shared_from_this_with(_M_ptr); }
	
	      template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
		       typename... _Args>
		friend __shared_ptr<_Tp1, _Lp1>
		__allocate_shared(const _Alloc& __a, _Args&&... __args);
	
	      // This constructor is used by __weak_ptr::lock() and
	      // shared_ptr::shared_ptr(const weak_ptr&, std::nothrow_t).
	      __shared_ptr(const __weak_ptr<_Tp, _Lp>& __r, std::nothrow_t)
	      : _M_refcount(__r._M_refcount, std::nothrow)
	      {
		_M_ptr = _M_refcount._M_get_use_count() ? __r._M_ptr : nullptr;
	      }
	
	      friend class __weak_ptr<_Tp, _Lp>;
	
	    private:
	
	      template<typename _Yp>
		using __esft_base_t = decltype(__enable_shared_from_this_base(
		      std::declval<const __shared_count<_Lp>&>(),
		      std::declval<_Yp*>()));
	
	      // Detect an accessible and unambiguous enable_shared_from_this base.
	      template<typename _Yp, typename = void>
		struct __has_esft_base
		: false_type { };
	
	      template<typename _Yp>
		struct __has_esft_base<_Yp, __void_t<__esft_base_t<_Yp>>>
		: __not_<is_array<_Tp>> { }; // No enable shared_from_this for arrays
	
	      template<typename _Yp, typename _Yp2 = typename remove_cv<_Yp>::type>
		typename enable_if<__has_esft_base<_Yp2>::value>::type
		_M_enable_shared_from_this_with(_Yp* __p) noexcept
		{
		  if (auto __base = __enable_shared_from_this_base(_M_refcount, __p))
		    __base->_M_weak_assign(const_cast<_Yp2*>(__p), _M_refcount);
		}
	
	      template<typename _Yp, typename _Yp2 = typename remove_cv<_Yp>::type>
		typename enable_if<!__has_esft_base<_Yp2>::value>::type
		_M_enable_shared_from_this_with(_Yp*) noexcept
		{ }
	
	      void*
	      _M_get_deleter(const std::type_info& __ti) const noexcept
	      { return _M_refcount._M_get_deleter(__ti); }
	
	      template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
	      template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
	
	      template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
		friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
	
	      template<typename _Del, typename _Tp1>
		friend _Del* get_deleter(const shared_ptr<_Tp1>&) noexcept;
	
	      element_type*	   _M_ptr;         // Contained pointer.
	      __shared_count<_Lp>  _M_refcount;    // Reference counter.
	    };
	
	
	  // 20.7.2.2.7 shared_ptr comparisons
	  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
	    inline bool
	    operator==(const __shared_ptr<_Tp1, _Lp>& __a,
		       const __shared_ptr<_Tp2, _Lp>& __b) noexcept
	    { return __a.get() == __b.get(); }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
	    { return !__a; }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
	    { return !__a; }
	
	  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
	    inline bool
	    operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
		       const __shared_ptr<_Tp2, _Lp>& __b) noexcept
	    { return __a.get() != __b.get(); }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
	    { return (bool)__a; }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
	    { return (bool)__a; }
	
	  template<typename _Tp, typename _Up, _Lock_policy _Lp>
	    inline bool
	    operator<(const __shared_ptr<_Tp, _Lp>& __a,
		      const __shared_ptr<_Up, _Lp>& __b) noexcept
	    {
	      using _Tp_elt = typename __shared_ptr<_Tp, _Lp>::element_type;
	      using _Up_elt = typename __shared_ptr<_Up, _Lp>::element_type;
	      using _Vp = typename common_type<_Tp_elt*, _Up_elt*>::type;
	      return less<_Vp>()(__a.get(), __b.get());
	    }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
	    {
	      using _Tp_elt = typename __shared_ptr<_Tp, _Lp>::element_type;
	      return less<_Tp_elt*>()(__a.get(), nullptr);
	    }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
	    {
	      using _Tp_elt = typename __shared_ptr<_Tp, _Lp>::element_type;
	      return less<_Tp_elt*>()(nullptr, __a.get());
	    }
	
	  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
	    inline bool
	    operator<=(const __shared_ptr<_Tp1, _Lp>& __a,
		       const __shared_ptr<_Tp2, _Lp>& __b) noexcept
	    { return !(__b < __a); }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
	    { return !(nullptr < __a); }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
	    { return !(__a < nullptr); }
	
	  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
	    inline bool
	    operator>(const __shared_ptr<_Tp1, _Lp>& __a,
		      const __shared_ptr<_Tp2, _Lp>& __b) noexcept
	    { return (__b < __a); }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
	    { return nullptr < __a; }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
	    { return __a < nullptr; }
	
	  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
	    inline bool
	    operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
		       const __shared_ptr<_Tp2, _Lp>& __b) noexcept
	    { return !(__a < __b); }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
	    { return !(__a < nullptr); }
	
	  template<typename _Tp, _Lock_policy _Lp>
	    inline bool
	    operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
	    { return !(nullptr < __a); }
	
	  // 20.7.2.2.8 shared_ptr specialized algorithms.
	  template<typename _Tp, _Lock_policy _Lp>
	    inline void
	    swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
	    { __a.swap(__b); }
	
	  // 20.7.2.2.9 shared_ptr casts
	
	  // The seemingly equivalent code:
	  // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
	  // will eventually result in undefined behaviour, attempting to
	  // delete the same object twice.
	  /// static_pointer_cast
	  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
	    inline __shared_ptr<_Tp, _Lp>
	    static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
	    {
	      using _Sp = __shared_ptr<_Tp, _Lp>;
	      return _Sp(__r, static_cast<typename _Sp::element_type*>(__r.get()));
	    }
	
	  // The seemingly equivalent code:
	  // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
	  // will eventually result in undefined behaviour, attempting to
	  // delete the same object twice.
	  /// const_pointer_cast
	  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
	    inline __shared_ptr<_Tp, _Lp>
	    const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
	    {
	      using _Sp = __shared_ptr<_Tp, _Lp>;
	      return _Sp(__r, const_cast<typename _Sp::element_type*>(__r.get()));
	    }
	
	  // The seemingly equivalent code:
	  // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
	  // will eventually result in undefined behaviour, attempting to
	  // delete the same object twice.
	  /// dynamic_pointer_cast
	  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
	    inline __shared_ptr<_Tp, _Lp>
	    dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
	    {
	      using _Sp = __shared_ptr<_Tp, _Lp>;
	      if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
		return _Sp(__r, __p);
	      return _Sp();
	    }
	
	#if __cplusplus > 201402L
	  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
	    inline __shared_ptr<_Tp, _Lp>
	    reinterpret_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
	    {
	      using _Sp = __shared_ptr<_Tp, _Lp>;
	      return _Sp(__r, reinterpret_cast<typename _Sp::element_type*>(__r.get()));
	    }
	#endif
	
	  template<typename _Tp, _Lock_policy _Lp>
	    class __weak_ptr
	    {
	      template<typename _Yp, typename _Res = void>
		using _Compatible = typename
		  enable_if<__sp_compatible_with<_Yp*, _Tp*>::value, _Res>::type;
	
	      // Constraint for assignment from shared_ptr and weak_ptr:
	      template<typename _Yp>
		using _Assignable = _Compatible<_Yp, __weak_ptr&>;
	
	    public:
	      using element_type = typename remove_extent<_Tp>::type;
	
	      constexpr __weak_ptr() noexcept
	      : _M_ptr(nullptr), _M_refcount()
	      { }
	
	      __weak_ptr(const __weak_ptr&) noexcept = default;
	
	      ~__weak_ptr() = default;
	
	      // The "obvious" converting constructor implementation:
	      //
	      //  template<typename _Tp1>
	      //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
	      //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
	      //    { }
	      //
	      // has a serious problem.
	      //
	      //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
	      //  conversion may require access to *__r._M_ptr (virtual inheritance).
	      //
	      // It is not possible to avoid spurious access violations since
	      // in multithreaded programs __r._M_ptr may be invalidated at any point.
	      template<typename _Yp, typename = _Compatible<_Yp>>
		__weak_ptr(const __weak_ptr<_Yp, _Lp>& __r) noexcept
		: _M_refcount(__r._M_refcount)
	        { _M_ptr = __r.lock().get(); }
	
	      template<typename _Yp, typename = _Compatible<_Yp>>
		__weak_ptr(const __shared_ptr<_Yp, _Lp>& __r) noexcept
		: _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
		{ }
	
	      __weak_ptr(__weak_ptr&& __r) noexcept
	      : _M_ptr(__r._M_ptr), _M_refcount(std::move(__r._M_refcount))
	      { __r._M_ptr = nullptr; }
	
	      template<typename _Yp, typename = _Compatible<_Yp>>
		__weak_ptr(__weak_ptr<_Yp, _Lp>&& __r) noexcept
		: _M_ptr(__r.lock().get()), _M_refcount(std::move(__r._M_refcount))
	        { __r._M_ptr = nullptr; }
	
	      __weak_ptr&
	      operator=(const __weak_ptr& __r) noexcept = default;
	
	      template<typename _Yp>
		_Assignable<_Yp>
		operator=(const __weak_ptr<_Yp, _Lp>& __r) noexcept
		{
		  _M_ptr = __r.lock().get();
		  _M_refcount = __r._M_refcount;
		  return *this;
		}
	
	      template<typename _Yp>
		_Assignable<_Yp>
		operator=(const __shared_ptr<_Yp, _Lp>& __r) noexcept
		{
		  _M_ptr = __r._M_ptr;
		  _M_refcount = __r._M_refcount;
		  return *this;
		}
	
	      __weak_ptr&
	      operator=(__weak_ptr&& __r) noexcept
	      {
		_M_ptr = __r._M_ptr;
		_M_refcount = std::move(__r._M_refcount);
		__r._M_ptr = nullptr;
		return *this;
	      }
	
	      template<typename _Yp>
		_Assignable<_Yp>
		operator=(__weak_ptr<_Yp, _Lp>&& __r) noexcept
		{
		  _M_ptr = __r.lock().get();
		  _M_refcount = std::move(__r._M_refcount);
		  __r._M_ptr = nullptr;
		  return *this;
		}
	
	      __shared_ptr<_Tp, _Lp>
	      lock() const noexcept
	      { return __shared_ptr<element_type, _Lp>(*this, std::nothrow); }
	
	      long
	      use_count() const noexcept
	      { return _M_refcount._M_get_use_count(); }
	
	      bool
	      expired() const noexcept
	      { return _M_refcount._M_get_use_count() == 0; }
	
	      template<typename _Tp1>
		bool
		owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const noexcept
		{ return _M_refcount._M_less(__rhs._M_refcount); }
	
	      template<typename _Tp1>
		bool
		owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const noexcept
		{ return _M_refcount._M_less(__rhs._M_refcount); }
	
	      void
	      reset() noexcept
	      { __weak_ptr().swap(*this); }
	
	      void
	      swap(__weak_ptr& __s) noexcept
	      {
		std::swap(_M_ptr, __s._M_ptr);
		_M_refcount._M_swap(__s._M_refcount);
	      }
	
	    private:
	      // Used by __enable_shared_from_this.
	      void
	      _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
	      {
		if (use_count() == 0)
		  {
		    _M_ptr = __ptr;
		    _M_refcount = __refcount;
		  }
	      }
	
	      template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
	      template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
	      friend class __enable_shared_from_this<_Tp, _Lp>;
	      friend class enable_shared_from_this<_Tp>;
	
	      element_type*	 _M_ptr;         // Contained pointer.
	      __weak_count<_Lp>  _M_refcount;    // Reference counter.
	    };
	
	  // 20.7.2.3.6 weak_ptr specialized algorithms.
	  template<typename _Tp, _Lock_policy _Lp>
	    inline void
	    swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
	    { __a.swap(__b); }
	
	  template<typename _Tp, typename _Tp1>
	    struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
	    {
	      bool
	      operator()(const _Tp& __lhs, const _Tp& __rhs) const noexcept
	      { return __lhs.owner_before(__rhs); }
	
	      bool
	      operator()(const _Tp& __lhs, const _Tp1& __rhs) const noexcept
	      { return __lhs.owner_before(__rhs); }
	
	      bool
	      operator()(const _Tp1& __lhs, const _Tp& __rhs) const noexcept
	      { return __lhs.owner_before(__rhs); }
	    };
	
	  template<>
	    struct _Sp_owner_less<void, void>
	    {
	      template<typename _Tp, typename _Up>
		auto
		operator()(const _Tp& __lhs, const _Up& __rhs) const noexcept
		-> decltype(__lhs.owner_before(__rhs))
		{ return __lhs.owner_before(__rhs); }
	
	      using is_transparent = void;
	    };
	
	  template<typename _Tp, _Lock_policy _Lp>
	    struct owner_less<__shared_ptr<_Tp, _Lp>>
	    : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
	    { };
	
	  template<typename _Tp, _Lock_policy _Lp>
	    struct owner_less<__weak_ptr<_Tp, _Lp>>
	    : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
	    { };
	
	
	  template<typename _Tp, _Lock_policy _Lp>
	    class __enable_shared_from_this
	    {
	    protected:
	      constexpr __enable_shared_from_this() noexcept { }
	
	      __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
	
	      __enable_shared_from_this&
	      operator=(const __enable_shared_from_this&) noexcept
	      { return *this; }
	
	      ~__enable_shared_from_this() { }
	
	    public:
	      __shared_ptr<_Tp, _Lp>
	      shared_from_this()
	      { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
	
	      __shared_ptr<const _Tp, _Lp>
	      shared_from_this() const
	      { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
	
	#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
	      __weak_ptr<_Tp, _Lp>
	      weak_from_this() noexcept
	      { return this->_M_weak_this; }
	
	      __weak_ptr<const _Tp, _Lp>
	      weak_from_this() const noexcept
	      { return this->_M_weak_this; }
	#endif
	
	    private:
	      template<typename _Tp1>
		void
		_M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
		{ _M_weak_this._M_assign(__p, __n); }
	
	      friend const __enable_shared_from_this*
	      __enable_shared_from_this_base(const __shared_count<_Lp>&,
					     const __enable_shared_from_this* __p)
	      { return __p; }
	
	      template<typename, _Lock_policy>
		friend class __shared_ptr;
	
	      mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
	    };
	
	  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy,
		   typename _Alloc, typename... _Args>
	    inline __shared_ptr<_Tp, _Lp>
	    __allocate_shared(const _Alloc& __a, _Args&&... __args)
	    {
	      return __shared_ptr<_Tp, _Lp>(_Sp_alloc_shared_tag<_Alloc>{__a},
					    std::forward<_Args>(__args)...);
	    }
	
	  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy,
		   typename... _Args>
	    inline __shared_ptr<_Tp, _Lp>
	    __make_shared(_Args&&... __args)
	    {
	      typedef typename std::remove_const<_Tp>::type _Tp_nc;
	      return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
						      std::forward<_Args>(__args)...);
	    }
	
	  /// std::hash specialization for __shared_ptr.
	  template<typename _Tp, _Lock_policy _Lp>
	    struct hash<__shared_ptr<_Tp, _Lp>>
	    : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
	    {
	      size_t
	      operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
	      {
		return hash<typename __shared_ptr<_Tp, _Lp>::element_type*>()(
		    __s.get());
	      }
	    };
	
	_GLIBCXX_END_NAMESPACE_VERSION
	} // namespace
	
	#endif // _SHARED_PTR_BASE_H