shared_ptr.h

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// <tr1/shared_ptr.h> -*- C++ -*-

// Copyright (C) 2007-2013 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/>.

//  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)

// GCC Note:  based on version 1.32.0 of the Boost library.

#ifndef _TR1_SHARED_PTR_H
#define _TR1_SHARED_PTR_H 1

namespace std _GLIBCXX_VISIBILITY(default)
{
namespace tr1
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  class bad_weak_ptr : public std::exception
  {
  public:
    virtual char const*
    what() const throw()
    { return "tr1::bad_weak_ptr"; }
  };

  // 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()
      : _M_use_count(1), _M_weak_count(1) { }
      
      virtual
      ~_Sp_counted_base() // nothrow 
      { }
  
      // Called when _M_use_count drops to zero, to release the resources
      // managed by *this.
      virtual void
      _M_dispose() = 0; // nothrow
      
      // Called when _M_weak_count drops to zero.
      virtual void
      _M_destroy() // nothrow
      { delete this; }
      
      virtual void*
      _M_get_deleter(const std::type_info&) = 0;

      void
      _M_add_ref_copy()
      { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
  
      void
      _M_add_ref_lock();
      
      void
      _M_release() // nothrow
      {
        // 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() // nothrow
      { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }

      void
      _M_weak_release() // nothrow
      {
        // 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 // nothrow
      {
        // No memory barrier is used here so there is no synchronization
        // with other threads.
        return const_cast<const volatile _Atomic_word&>(_M_use_count);
      }

    private:  
      _Sp_counted_base(_Sp_counted_base const&);
      _Sp_counted_base& operator=(_Sp_counted_base const&);

      _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 (__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_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_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<typename _Ptr, typename _Deleter, _Lock_policy _Lp>
    class _Sp_counted_base_impl
    : public _Sp_counted_base<_Lp>
    {
    public:
      // Precondition: __d(__p) must not throw.
      _Sp_counted_base_impl(_Ptr __p, _Deleter __d)
      : _M_ptr(__p), _M_del(__d) { }
    
      virtual void
      _M_dispose() // nothrow
      { _M_del(_M_ptr); }
      
      virtual void*
      _M_get_deleter(const std::type_info& __ti)
      {
#ifdef __GXX_RTTI
        return __ti == typeid(_Deleter) ? &_M_del : 0;
#else
        return 0;
#endif
      }
      
    private:
      _Sp_counted_base_impl(const _Sp_counted_base_impl&);
      _Sp_counted_base_impl& operator=(const _Sp_counted_base_impl&);
      
      _Ptr      _M_ptr;  // copy constructor must not throw
      _Deleter  _M_del;  // copy constructor must not throw
    };

  template<_Lock_policy _Lp = __default_lock_policy>
    class __weak_count;

  template<typename _Tp>
    struct _Sp_deleter
    {
      typedef void result_type;
      typedef _Tp* argument_type;
      void operator()(_Tp* __p) const { delete __p; }
    };

  template<_Lock_policy _Lp = __default_lock_policy>
    class __shared_count
    {
    public: 
      __shared_count()
      : _M_pi(0) // nothrow
      { }
  
      template<typename _Ptr>
        __shared_count(_Ptr __p) : _M_pi(0)
        {
      __try
        {
          typedef typename std::tr1::remove_pointer<_Ptr>::type _Tp;
          _M_pi = new _Sp_counted_base_impl<_Ptr, _Sp_deleter<_Tp>, _Lp>(
              __p, _Sp_deleter<_Tp>());
        }
      __catch(...)
        {
          delete __p;
          __throw_exception_again;
        }
    }

      template<typename _Ptr, typename _Deleter>
        __shared_count(_Ptr __p, _Deleter __d) : _M_pi(0)
        {
      __try
        {
          _M_pi = new _Sp_counted_base_impl<_Ptr, _Deleter, _Lp>(__p, __d);
        }
      __catch(...)
        {
          __d(__p); // Call _Deleter on __p.
          __throw_exception_again;
        }
    }

      // Special case for auto_ptr<_Tp> to provide the strong guarantee.
      template<typename _Tp>
        explicit
        __shared_count(std::auto_ptr<_Tp>& __r)
    : _M_pi(new _Sp_counted_base_impl<_Tp*,
        _Sp_deleter<_Tp>, _Lp >(__r.get(), _Sp_deleter<_Tp>()))
        { __r.release(); }

      // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
      explicit
      __shared_count(const __weak_count<_Lp>& __r);
  
      ~__shared_count() // nothrow
      {
    if (_M_pi != 0)
      _M_pi->_M_release();
      }
      
      __shared_count(const __shared_count& __r)
      : _M_pi(__r._M_pi) // nothrow
      {
    if (_M_pi != 0)
      _M_pi->_M_add_ref_copy();
      }
  
      __shared_count&
      operator=(const __shared_count& __r) // nothrow
      {
    _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) // nothrow
      {
    _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
    __r._M_pi = _M_pi;
    _M_pi = __tmp;
      }
  
      long
      _M_get_use_count() const // nothrow
      { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }

      bool
      _M_unique() const // nothrow
      { return this->_M_get_use_count() == 1; }
      
      friend inline bool
      operator==(const __shared_count& __a, const __shared_count& __b)
      { return __a._M_pi == __b._M_pi; }
  
      friend inline bool
      operator<(const __shared_count& __a, const __shared_count& __b)
      { return std::less<_Sp_counted_base<_Lp>*>()(__a._M_pi, __b._M_pi); }
  
      void*
      _M_get_deleter(const std::type_info& __ti) const
      { return _M_pi ? _M_pi->_M_get_deleter(__ti) : 0; }

    private:
      friend class __weak_count<_Lp>;

      _Sp_counted_base<_Lp>*  _M_pi;
    };


  template<_Lock_policy _Lp>
    class __weak_count
    {
    public:
      __weak_count()
      : _M_pi(0) // nothrow
      { }
  
      __weak_count(const __shared_count<_Lp>& __r)
      : _M_pi(__r._M_pi) // nothrow
      {
    if (_M_pi != 0)
      _M_pi->_M_weak_add_ref();
      }
      
      __weak_count(const __weak_count<_Lp>& __r)
      : _M_pi(__r._M_pi) // nothrow
      {
    if (_M_pi != 0)
      _M_pi->_M_weak_add_ref();
      }
      
      ~__weak_count() // nothrow
      {
    if (_M_pi != 0)
      _M_pi->_M_weak_release();
      }
      
      __weak_count<_Lp>&
      operator=(const __shared_count<_Lp>& __r) // nothrow
      {
    _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
    if (__tmp != 0)
      __tmp->_M_weak_add_ref();
    if (_M_pi != 0)
      _M_pi->_M_weak_release();
    _M_pi = __tmp;  
    return *this;
      }
      
      __weak_count<_Lp>&
      operator=(const __weak_count<_Lp>& __r) // nothrow
      {
    _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
    if (__tmp != 0)
      __tmp->_M_weak_add_ref();
    if (_M_pi != 0)
      _M_pi->_M_weak_release();
    _M_pi = __tmp;
    return *this;
      }

      void
      _M_swap(__weak_count<_Lp>& __r) // nothrow
      {
    _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
    __r._M_pi = _M_pi;
    _M_pi = __tmp;
      }
  
      long
      _M_get_use_count() const // nothrow
      { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }

      friend inline bool
      operator==(const __weak_count<_Lp>& __a, const __weak_count<_Lp>& __b)
      { return __a._M_pi == __b._M_pi; }
      
      friend inline bool
      operator<(const __weak_count<_Lp>& __a, const __weak_count<_Lp>& __b)
      { return std::less<_Sp_counted_base<_Lp>*>()(__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 != 0)
    _M_pi->_M_add_ref_lock();
      else
    __throw_bad_weak_ptr();
    }

  // 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>
    class enable_shared_from_this;

  // 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*);

  // Friend of enable_shared_from_this.
  template<typename _Tp1, typename _Tp2>
    void
    __enable_shared_from_this_helper(const __shared_count<>&,
                     const enable_shared_from_this<_Tp1>*,
                     const _Tp2*);

  template<_Lock_policy _Lp>
    inline void
    __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...)
    { }


  struct __static_cast_tag { };
  struct __const_cast_tag { };
  struct __dynamic_cast_tag { };

  // A smart pointer with reference-counted copy semantics.  The
  // object pointed to is deleted when the last shared_ptr pointing to
  // it is destroyed or reset.
  template<typename _Tp, _Lock_policy _Lp>
    class __shared_ptr
    {
    public:
      typedef _Tp   element_type;
      
      __shared_ptr()
      : _M_ptr(0), _M_refcount() // never throws
      { }

      template<typename _Tp1>
        explicit
        __shared_ptr(_Tp1* __p)
    : _M_ptr(__p), _M_refcount(__p)
        {
      __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
      typedef int _IsComplete[sizeof(_Tp1)];
      __enable_shared_from_this_helper(_M_refcount, __p, __p);
    }

      template<typename _Tp1, typename _Deleter>
        __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);
    }
      
      //  generated copy constructor, assignment, destructor are fine.
      
      template<typename _Tp1>
        __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r)
    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
        { __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>) }

      template<typename _Tp1>
        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 (__cplusplus < 201103L) || _GLIBCXX_USE_DEPRECATED
      // Postcondition: use_count() == 1 and __r.get() == 0
      template<typename _Tp1>
        explicit
        __shared_ptr(std::auto_ptr<_Tp1>& __r)
    : _M_ptr(__r.get()), _M_refcount()
        { // TODO requries delete __r.release() well-formed
      __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
      typedef int _IsComplete[sizeof(_Tp1)];
      _Tp1* __tmp = __r.get();
      _M_refcount = __shared_count<_Lp>(__r);
      __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
    }

#endif

      template<typename _Tp1>
        __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, __static_cast_tag)
    : _M_ptr(static_cast<element_type*>(__r._M_ptr)),
      _M_refcount(__r._M_refcount)
        { }

      template<typename _Tp1>
        __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, __const_cast_tag)
    : _M_ptr(const_cast<element_type*>(__r._M_ptr)),
      _M_refcount(__r._M_refcount)
        { }

      template<typename _Tp1>
        __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, __dynamic_cast_tag)
    : _M_ptr(dynamic_cast<element_type*>(__r._M_ptr)),
      _M_refcount(__r._M_refcount)
        {
      if (_M_ptr == 0) // need to allocate new counter -- the cast failed
        _M_refcount = __shared_count<_Lp>();
    }

      template<typename _Tp1>
        __shared_ptr&
        operator=(const __shared_ptr<_Tp1, _Lp>& __r) // never throws
        {
      _M_ptr = __r._M_ptr;
      _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
      return *this;
    }

#if (__cplusplus < 201103L) || _GLIBCXX_USE_DEPRECATED
      template<typename _Tp1>
        __shared_ptr&
        operator=(std::auto_ptr<_Tp1>& __r)
        {
      __shared_ptr(__r).swap(*this);
      return *this;
    }
#endif

      void
      reset() // never throws
      { __shared_ptr().swap(*this); }

      template<typename _Tp1>
        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<typename _Tp1, typename _Deleter>
        void
        reset(_Tp1* __p, _Deleter __d)
        { __shared_ptr(__p, __d).swap(*this); }

      // Allow class instantiation when _Tp is [cv-qual] void.
      typename std::tr1::add_reference<_Tp>::type
      operator*() const // never throws
      {
    _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
    return *_M_ptr;
      }

      _Tp*
      operator->() const // never throws
      {
    _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
    return _M_ptr;
      }
    
      _Tp*
      get() const // never throws
      { return _M_ptr; }

      // Implicit conversion to "bool"
    private:
      typedef _Tp* __shared_ptr::*__unspecified_bool_type;

    public:
      operator __unspecified_bool_type() const // never throws
      { return _M_ptr == 0 ? 0 : &__shared_ptr::_M_ptr; }

      bool
      unique() const // never throws
      { return _M_refcount._M_unique(); }

      long
      use_count() const // never throws
      { return _M_refcount._M_get_use_count(); }

      void
      swap(__shared_ptr<_Tp, _Lp>& __other) // never throws
      {
    std::swap(_M_ptr, __other._M_ptr);
    _M_refcount._M_swap(__other._M_refcount);
      }

    private:
      void*
      _M_get_deleter(const std::type_info& __ti) const
      { return _M_refcount._M_get_deleter(__ti); }

      template<typename _Tp1, _Lock_policy _Lp1>
        bool
        _M_less(const __shared_ptr<_Tp1, _Lp1>& __rhs) const
        { return _M_refcount < __rhs._M_refcount; }

      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>&);

      // Friends injected into enclosing namespace and found by ADL:
      template<typename _Tp1>
        friend inline bool
        operator==(const __shared_ptr& __a, const __shared_ptr<_Tp1, _Lp>& __b)
        { return __a.get() == __b.get(); }

      template<typename _Tp1>
        friend inline bool
        operator!=(const __shared_ptr& __a, const __shared_ptr<_Tp1, _Lp>& __b)
        { return __a.get() != __b.get(); }

      template<typename _Tp1>
        friend inline bool
        operator<(const __shared_ptr& __a, const __shared_ptr<_Tp1, _Lp>& __b)
        { return __a._M_less(__b); }

      _Tp*             _M_ptr;         // Contained pointer.
      __shared_count<_Lp>  _M_refcount;    // Reference counter.
    };

  // 2.2.3.8 shared_ptr specialized algorithms.
  template<typename _Tp, _Lock_policy _Lp>
    inline void
    swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b)
    { __a.swap(__b); }

  // 2.2.3.9 shared_ptr casts
  /*  The seemingly equivalent
   *           shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
   *  will eventually result in undefined behaviour,
   *  attempting to delete the same object twice.
   */
  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
    inline __shared_ptr<_Tp, _Lp>
    static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
    { return __shared_ptr<_Tp, _Lp>(__r, __static_cast_tag()); }

  /*  The seemingly equivalent
   *           shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
   *  will eventually result in undefined behaviour,
   *  attempting to delete the same object twice.
   */
  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
    inline __shared_ptr<_Tp, _Lp>
    const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
    { return __shared_ptr<_Tp, _Lp>(__r, __const_cast_tag()); }

  /*  The seemingly equivalent
   *           shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
   *  will eventually result in undefined behaviour,
   *  attempting to delete the same object twice.
   */
  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
    inline __shared_ptr<_Tp, _Lp>
    dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
    { return __shared_ptr<_Tp, _Lp>(__r, __dynamic_cast_tag()); }

  // 2.2.3.7 shared_ptr I/O
  template<typename _Ch, typename _Tr, typename _Tp, _Lock_policy _Lp>
    std::basic_ostream<_Ch, _Tr>&
    operator<<(std::basic_ostream<_Ch, _Tr>& __os, 
           const __shared_ptr<_Tp, _Lp>& __p)
    {
      __os << __p.get();
      return __os;
    }

  // 2.2.3.10 shared_ptr get_deleter (experimental)
  template<typename _Del, typename _Tp, _Lock_policy _Lp>
    inline _Del*
    get_deleter(const __shared_ptr<_Tp, _Lp>& __p)
    {
#ifdef __GXX_RTTI
      return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del)));
#else
      return 0;
#endif
    }


  template<typename _Tp, _Lock_policy _Lp>
    class __weak_ptr
    {
    public:
      typedef _Tp element_type;
      
      __weak_ptr()
      : _M_ptr(0), _M_refcount() // never throws
      { }

      // Generated copy constructor, assignment, destructor are fine.
      
      // 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 _Tp1>
        __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
    : _M_refcount(__r._M_refcount) // never throws
        {
      __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
      _M_ptr = __r.lock().get();
    }

      template<typename _Tp1>
        __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r)
    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
        { __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>) }

      template<typename _Tp1>
        __weak_ptr&
        operator=(const __weak_ptr<_Tp1, _Lp>& __r) // never throws
        {
      _M_ptr = __r.lock().get();
      _M_refcount = __r._M_refcount;
      return *this;
    }
      
      template<typename _Tp1>
        __weak_ptr&
        operator=(const __shared_ptr<_Tp1, _Lp>& __r) // never throws
        {
      _M_ptr = __r._M_ptr;
      _M_refcount = __r._M_refcount;
      return *this;
    }

      __shared_ptr<_Tp, _Lp>
      lock() const // never throws
      {
#ifdef __GTHREADS
    // Optimization: avoid throw overhead.
    if (expired())
      return __shared_ptr<element_type, _Lp>();

    __try
      {
        return __shared_ptr<element_type, _Lp>(*this);
      }
    __catch(const bad_weak_ptr&)
      {
        // Q: How can we get here?
        // A: Another thread may have invalidated r after the
        //    use_count test above.
        return __shared_ptr<element_type, _Lp>();
      }
    
#else
    // Optimization: avoid try/catch overhead when single threaded.
    return expired() ? __shared_ptr<element_type, _Lp>()
                     : __shared_ptr<element_type, _Lp>(*this);

#endif
      } // XXX MT

      long
      use_count() const // never throws
      { return _M_refcount._M_get_use_count(); }

      bool
      expired() const // never throws
      { return _M_refcount._M_get_use_count() == 0; }
      
      void
      reset() // never throws
      { __weak_ptr().swap(*this); }

      void
      swap(__weak_ptr& __s) // never throws
      {
    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)
      {
    _M_ptr = __ptr;
    _M_refcount = __refcount;
      }

      template<typename _Tp1>
        bool
        _M_less(const __weak_ptr<_Tp1, _Lp>& __rhs) const
        { return _M_refcount < __rhs._M_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>;

      // Friend injected into namespace and found by ADL.
      template<typename _Tp1>
        friend inline bool
        operator<(const __weak_ptr& __lhs, const __weak_ptr<_Tp1, _Lp>& __rhs)
        { return __lhs._M_less(__rhs); }

      _Tp*           _M_ptr;         // Contained pointer.
      __weak_count<_Lp>  _M_refcount;    // Reference counter.
    };

  // 2.2.4.7 weak_ptr specialized algorithms.
  template<typename _Tp, _Lock_policy _Lp>
    inline void
    swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b)
    { __a.swap(__b); }


  template<typename _Tp, _Lock_policy _Lp>
    class __enable_shared_from_this
    {
    protected:
      __enable_shared_from_this() { }
      
      __enable_shared_from_this(const __enable_shared_from_this&) { }
      
      __enable_shared_from_this&
      operator=(const __enable_shared_from_this&)
      { 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); }

    private:
      template<typename _Tp1>
        void
        _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const
        { _M_weak_this._M_assign(__p, __n); }

      template<typename _Tp1>
        friend void
        __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
                     const __enable_shared_from_this* __pe,
                     const _Tp1* __px)
        {
      if (__pe != 0)
        __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
    }

      mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
    };


  // The actual shared_ptr, with forwarding constructors and
  // assignment operators.
  template<typename _Tp>
    class shared_ptr
    : public __shared_ptr<_Tp>
    {
    public:
      shared_ptr()
      : __shared_ptr<_Tp>() { }

      template<typename _Tp1>
        explicit
        shared_ptr(_Tp1* __p)
    : __shared_ptr<_Tp>(__p) { }

      template<typename _Tp1, typename _Deleter>
        shared_ptr(_Tp1* __p, _Deleter __d)
    : __shared_ptr<_Tp>(__p, __d) { }

      template<typename _Tp1>
        shared_ptr(const shared_ptr<_Tp1>& __r)
    : __shared_ptr<_Tp>(__r) { }

      template<typename _Tp1>
        explicit
        shared_ptr(const weak_ptr<_Tp1>& __r)
    : __shared_ptr<_Tp>(__r) { }

#if (__cplusplus < 201103L) || _GLIBCXX_USE_DEPRECATED
      template<typename _Tp1>
        explicit
        shared_ptr(std::auto_ptr<_Tp1>& __r)
    : __shared_ptr<_Tp>(__r) { }
#endif

      template<typename _Tp1>
        shared_ptr(const shared_ptr<_Tp1>& __r, __static_cast_tag)
    : __shared_ptr<_Tp>(__r, __static_cast_tag()) { }

      template<typename _Tp1>
        shared_ptr(const shared_ptr<_Tp1>& __r, __const_cast_tag)
    : __shared_ptr<_Tp>(__r, __const_cast_tag()) { }

      template<typename _Tp1>
        shared_ptr(const shared_ptr<_Tp1>& __r, __dynamic_cast_tag)
    : __shared_ptr<_Tp>(__r, __dynamic_cast_tag()) { }

      template<typename _Tp1>
        shared_ptr&
        operator=(const shared_ptr<_Tp1>& __r) // never throws
        {
      this->__shared_ptr<_Tp>::operator=(__r);
      return *this;
    }

#if (__cplusplus < 201103L) || _GLIBCXX_USE_DEPRECATED
      template<typename _Tp1>
        shared_ptr&
        operator=(std::auto_ptr<_Tp1>& __r)
        {
      this->__shared_ptr<_Tp>::operator=(__r);
      return *this;
    }
#endif
    };

  // 2.2.3.8 shared_ptr specialized algorithms.
  template<typename _Tp>
    inline void
    swap(__shared_ptr<_Tp>& __a, __shared_ptr<_Tp>& __b)
    { __a.swap(__b); }

  template<typename _Tp, typename _Tp1>
    inline shared_ptr<_Tp>
    static_pointer_cast(const shared_ptr<_Tp1>& __r)
    { return shared_ptr<_Tp>(__r, __static_cast_tag()); }

  template<typename _Tp, typename _Tp1>
    inline shared_ptr<_Tp>
    const_pointer_cast(const shared_ptr<_Tp1>& __r)
    { return shared_ptr<_Tp>(__r, __const_cast_tag()); }

  template<typename _Tp, typename _Tp1>
    inline shared_ptr<_Tp>
    dynamic_pointer_cast(const shared_ptr<_Tp1>& __r)
    { return shared_ptr<_Tp>(__r, __dynamic_cast_tag()); }


  // The actual weak_ptr, with forwarding constructors and
  // assignment operators.
  template<typename _Tp>
    class weak_ptr
    : public __weak_ptr<_Tp>
    {
    public:
      weak_ptr()
      : __weak_ptr<_Tp>() { }
      
      template<typename _Tp1>
        weak_ptr(const weak_ptr<_Tp1>& __r)
    : __weak_ptr<_Tp>(__r) { }

      template<typename _Tp1>
        weak_ptr(const shared_ptr<_Tp1>& __r)
    : __weak_ptr<_Tp>(__r) { }

      template<typename _Tp1>
        weak_ptr&
        operator=(const weak_ptr<_Tp1>& __r) // never throws
        {
      this->__weak_ptr<_Tp>::operator=(__r);
      return *this;
    }

      template<typename _Tp1>
        weak_ptr&
        operator=(const shared_ptr<_Tp1>& __r) // never throws
        {
      this->__weak_ptr<_Tp>::operator=(__r);
      return *this;
    }

      shared_ptr<_Tp>
      lock() const // never throws
      {
#ifdef __GTHREADS
    if (this->expired())
      return shared_ptr<_Tp>();

    __try
      {
        return shared_ptr<_Tp>(*this);
      }
    __catch(const bad_weak_ptr&)
      {
        return shared_ptr<_Tp>();
      }
#else
    return this->expired() ? shared_ptr<_Tp>()
                           : shared_ptr<_Tp>(*this);
#endif
      }
    };

  template<typename _Tp>
    class enable_shared_from_this
    {
    protected:
      enable_shared_from_this() { }
      
      enable_shared_from_this(const enable_shared_from_this&) { }

      enable_shared_from_this&
      operator=(const enable_shared_from_this&)
      { return *this; }

      ~enable_shared_from_this() { }

    public:
      shared_ptr<_Tp>
      shared_from_this()
      { return shared_ptr<_Tp>(this->_M_weak_this); }

      shared_ptr<const _Tp>
      shared_from_this() const
      { return shared_ptr<const _Tp>(this->_M_weak_this); }

    private:
      template<typename _Tp1>
        void
        _M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const
        { _M_weak_this._M_assign(__p, __n); }

      template<typename _Tp1>
        friend void
        __enable_shared_from_this_helper(const __shared_count<>& __pn,
                     const enable_shared_from_this* __pe,
                     const _Tp1* __px)
        {
      if (__pe != 0)
        __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
    }

      mutable weak_ptr<_Tp>  _M_weak_this;
    };

_GLIBCXX_END_NAMESPACE_VERSION
}
}

#endif // _TR1_SHARED_PTR_H