Subversion Repositories Kolibri OS

// shared_ptr and weak_ptr implementation details -*- C++ -*-

// Copyright (C) 2007-2015 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

// .

// 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 

#include 

namespace std _GLIBCXX_VISIBILITY(default)

{

_GLIBCXX_BEGIN_NAMESPACE_VERSION

#if _GLIBCXX_USE_DEPRECATED

  template class auto_ptr;

#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)

	      {

	        _GLIBCXX_READ_MEM_BARRIER;

	        _GLIBCXX_WRITE_MEM_BARRIER;

	      }

            // 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()

	        _GLIBCXX_READ_MEM_BARRIER;

	        _GLIBCXX_WRITE_MEM_BARRIER;

	      }

	    _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

    class __shared_ptr;

  template

    class __weak_ptr;

  template

    class __enable_shared_from_this;

  template

    class shared_ptr;

  template

    class weak_ptr;

  template

    struct owner_less;

  template

    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

    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::_M_dispose() noexcept { }

  template<>

    inline void

    _Sp_counted_ptr::_M_dispose() noexcept { }

  template<>

    inline void

    _Sp_counted_ptr::_M_dispose() noexcept { }

  template

	   bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>

    struct _Sp_ebo_helper;

  /// Specialization using EBO.

  template

    struct _Sp_ebo_helper<_Nm, _Tp, true> : private _Tp

    {

      explicit _Sp_ebo_helper(const _Tp& __tp) : _Tp(__tp) { }

      static _Tp&

      _S_get(_Sp_ebo_helper& __eboh) { return static_cast<_Tp&>(__eboh); }

    };

  /// Specialization not using EBO.

  template

    struct _Sp_ebo_helper<_Nm, _Tp, false>

    {

      explicit _Sp_ebo_helper(const _Tp& __tp) : _M_tp(__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

    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(__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, __d, _Alloc()) { }

      // __d(__p) must not throw.

      _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept

      : _M_impl(__p, __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 { };

  template

    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>;

      template

	_Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)

	: _M_impl(__a)

	{

	  // _GLIBCXX_RESOLVE_LIB_DEFECTS

	  // 2070.  allocate_shared should use allocator_traits::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();

      }

      // Sneaky trick so __shared_ptr can get the managed pointer

      virtual void*

      _M_get_deleter(const std::type_info& __ti) noexcept

      {

#if __cpp_rtti

	if (__ti == typeid(_Sp_make_shared_tag))

	  return const_cast::type*>(_M_ptr());

#endif

	return nullptr;

      }

    private:

      _Tp* _M_ptr() noexcept { return _M_impl._M_storage._M_ptr(); }

      _Impl _M_impl;

    };

  template<_Lock_policy _Lp>

    class __shared_count

    {

    public:

      constexpr __shared_count() noexcept : _M_pi(0)

      { }

      template

        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

	__shared_count(_Ptr __p, _Deleter __d)

	: __shared_count(__p, std::move(__d), allocator())

	{ }

      template

	__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

	__shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,

		       _Args&&... __args)

	: _M_pi(0)

	{

	  typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;

	  typename _Sp_cp_type::__allocator_type __a2(__a);

	  auto __guard = std::__allocate_guarded(__a2);

	  _Sp_cp_type* __mem = __guard.get();

	  ::new (__mem) _Sp_cp_type(std::move(__a),

				    std::forward<_Args>(__args)...);

	  _M_pi = __mem;

	  __guard = nullptr;

	}

#if _GLIBCXX_USE_DEPRECATED

      // Special case for auto_ptr<_Tp> to provide the strong guarantee.

      template

        explicit

	__shared_count(std::auto_ptr<_Tp>&& __r);

#endif

      // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.

      template

        explicit

	__shared_count(std::unique_ptr<_Tp, _Del>&& __r) : _M_pi(0)

	{

	  using _Ptr = typename unique_ptr<_Tp, _Del>::pointer;

	  using _Del2 = typename conditional::value,

	      reference_wrapper::type>,

	      _Del>::type;

	  using _Sp_cd_type

	    = _Sp_counted_deleter<_Ptr, _Del2, allocator, _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;

    }

  // Support for enable_shared_from_this.

  // Friend of __enable_shared_from_this.

  template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>

    void

    __enable_shared_from_this_helper(const __shared_count<_Lp>&,

				     const __enable_shared_from_this<_Tp1,

				     _Lp>*, const _Tp2*) noexcept;

  // Friend of enable_shared_from_this.

  template

    void

    __enable_shared_from_this_helper(const __shared_count<>&,

				     const enable_shared_from_this<_Tp1>*,

				     const _Tp2*) noexcept;

  template<_Lock_policy _Lp>

    inline void

    __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept

    { }

  template

    class __shared_ptr

    {

      template

	using _Convertible

	  = typename enable_if::value>::type;

    public:

      typedef _Tp   element_type;

      constexpr __shared_ptr() noexcept

      : _M_ptr(0), _M_refcount()

      { }

      template

	explicit __shared_ptr(_Tp1* __p)

        : _M_ptr(__p), _M_refcount(__p)

	{

	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)

	  static_assert( !is_void<_Tp1>::value, "incomplete type" );

	  static_assert( sizeof(_Tp1) > 0, "incomplete type" );

	  __enable_shared_from_this_helper(_M_refcount, __p, __p);

	}

      template

	__shared_ptr(_Tp1* __p, _Deleter __d)

	: _M_ptr(__p), _M_refcount(__p, __d)

	{

	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)

	  // TODO requires _Deleter CopyConstructible and __d(__p) well-formed

	  __enable_shared_from_this_helper(_M_refcount, __p, __p);

	}

      template

	__shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)

	: _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))

	{

	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)

	  // TODO requires _Deleter CopyConstructible and __d(__p) well-formed

	  __enable_shared_from_this_helper(_M_refcount, __p, __p);

	}

      template

	__shared_ptr(nullptr_t __p, _Deleter __d)

	: _M_ptr(0), _M_refcount(__p, __d)

	{ }

      template

        __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)

	: _M_ptr(0), _M_refcount(__p, __d, std::move(__a))

	{ }

      template

	__shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __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>

	__shared_ptr(const __shared_ptr<_Tp1, _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>

	__shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r) noexcept

	: _M_ptr(__r._M_ptr), _M_refcount()

	{

	  _M_refcount._M_swap(__r._M_refcount);

	  __r._M_ptr = 0;

	}

      template

	explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)

	: _M_refcount(__r._M_refcount) // may throw

	{

	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)

	  // 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

	       = _Convertible::pointer>>

	__shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)

	: _M_ptr(__r.get()), _M_refcount()

	{

	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)

	  auto __raw = _S_raw_ptr(__r.get());

	  _M_refcount = __shared_count<_Lp>(std::move(__r));

	  __enable_shared_from_this_helper(_M_refcount, __raw, __raw);

	}

#if _GLIBCXX_USE_DEPRECATED

      // Postcondition: use_count() == 1 and __r.get() == 0

      template

	__shared_ptr(std::auto_ptr<_Tp1>&& __r);

#endif

      constexpr __shared_ptr(nullptr_t) noexcept : __shared_ptr() { }

      template

	__shared_ptr&

	operator=(const __shared_ptr<_Tp1, _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

      template

	__shared_ptr&

	operator=(std::auto_ptr<_Tp1>&& __r)

	{

	  __shared_ptr(std::move(__r)).swap(*this);

	  return *this;

	}

#endif

      __shared_ptr&

      operator=(__shared_ptr&& __r) noexcept

      {

	__shared_ptr(std::move(__r)).swap(*this);

	return *this;

      }

      template

	__shared_ptr&

	operator=(__shared_ptr<_Tp1, _Lp>&& __r) noexcept

	{

	  __shared_ptr(std::move(__r)).swap(*this);

	  return *this;

	}

      template

	__shared_ptr&

	operator=(std::unique_ptr<_Tp1, _Del>&& __r)

	{

	  __shared_ptr(std::move(__r)).swap(*this);

	  return *this;

	}

      void

      reset() noexcept

      { __shared_ptr().swap(*this); }

      template

	void

	reset(_Tp1* __p) // _Tp1 must be complete.

	{

	  // Catch self-reset errors.

	  _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);

	  __shared_ptr(__p).swap(*this);

	}

      template

	void

	reset(_Tp1* __p, _Deleter __d)

	{ __shared_ptr(__p, __d).swap(*this); }

      template

	void

        reset(_Tp1* __p, _Deleter __d, _Alloc __a)

        { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }

      // Allow class instantiation when _Tp is [cv-qual] void.

      typename std::add_lvalue_reference<_Tp>::type

      operator*() const noexcept

      {

	_GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);

	return *_M_ptr;

      }

      _Tp*

      operator->() const noexcept

      {

	_GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);

	return _M_ptr;

      }

      _Tp*

      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

	bool

	owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const

	{ return _M_refcount._M_less(__rhs._M_refcount); }

      template

	bool

	owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const

	{ return _M_refcount._M_less(__rhs._M_refcount); }

#if __cpp_rtti

    protected:

      // This constructor is non-standard, it is used by allocate_shared.

      template

	__shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,

		     _Args&&... __args)

	: _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,

				std::forward<_Args>(__args)...)

	{

	  // _M_ptr needs to point to the newly constructed object.

	  // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.

	  void* __p = _M_refcount._M_get_deleter(typeid(__tag));

	  _M_ptr = static_cast<_Tp*>(__p);

	  __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);

	}

#else

      template

        struct _Deleter

        {

          void operator()(typename _Alloc::value_type* __ptr)

          {

	    __allocated_ptr<_Alloc> __guard{ _M_alloc, __ptr };

	    allocator_traits<_Alloc>::destroy(_M_alloc, __guard.get());

          }

          _Alloc _M_alloc;

        };

      template

	__shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,

		     _Args&&... __args)

	: _M_ptr(), _M_refcount()

	{