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#ifndef BOOST_WEAK_PTR_H_INCLUDED
#define BOOST_WEAK_PTR_H_INCLUDED
//
// weak_ptr.h
//
// Copyright (c) 2001, 2002, 2003 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)
//
// See http://www.boost.org/libs/smart_ptr/weak_ptr.htm for documentation.
//
#include <boost/shared_ptr.hpp>
#ifdef BOOST_MSVC // moved here to work around VC++ compiler crash
# pragma warning(push)
# pragma warning(disable:4284) // odd return type for operator->
#endif
namespace boost
{
template<class T> class weak_ptr
{
private:
// Borland 5.5.1 specific workarounds
typedef weak_ptr<T> this_type;
public:
typedef T element_type;
weak_ptr(): px(0), pn() // never throws in 1.30+
{
}
// generated copy constructor, assignment, destructor are fine
//
// The "obvious" converting constructor implementation:
//
// template<class Y>
// weak_ptr(weak_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
// {
// }
//
// has a serious problem.
//
// r.px may already have been invalidated. The px(r.px)
// conversion may require access to *r.px (virtual inheritance).
//
// It is not possible to avoid spurious access violations since
// in multithreaded programs r.px may be invalidated at any point.
//
template<class Y>
weak_ptr(weak_ptr<Y> const & r): pn(r.pn) // never throws
{
px = r.lock().get();
}
template<class Y>
weak_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
{
}
#if !defined(BOOST_MSVC) || (BOOST_MSVC > 1200)
template<class Y>
weak_ptr & operator=(weak_ptr<Y> const & r) // never throws
{
px = r.lock().get();
pn = r.pn;
return *this;
}
template<class Y>
weak_ptr & operator=(shared_ptr<Y> const & r) // never throws
{
px = r.px;
pn = r.pn;
return *this;
}
#endif
shared_ptr<T> lock() const // never throws
{
#if defined(BOOST_HAS_THREADS)
// optimization: avoid throw overhead
if(expired())
{
return shared_ptr<element_type>();
}
try
{
return shared_ptr<element_type>(*this);
}
catch(bad_weak_ptr const &)
{
// Q: how can we get here?
// A: another thread may have invalidated r after the use_count test above.
return shared_ptr<element_type>();
}
#else
// optimization: avoid try/catch overhead when single threaded
return expired()? shared_ptr<element_type>(): shared_ptr<element_type>(*this);
#endif
}
long use_count() const // never throws
{
return pn.use_count();
}
bool expired() const // never throws
{
return pn.use_count() == 0;
}
void reset() // never throws in 1.30+
{
this_type().swap(*this);
}
void swap(this_type & other) // never throws
{
std::swap(px, other.px);
pn.swap(other.pn);
}
void _internal_assign(T * px2, detail::shared_count const & pn2)
{
px = px2;
pn = pn2;
}
template<class Y> bool _internal_less(weak_ptr<Y> const & rhs) const
{
return pn < rhs.pn;
}
// Tasteless as this may seem, making all members public allows member templates
// to work in the absence of member template friends. (Matthew Langston)
#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
private:
template<class Y> friend class weak_ptr;
template<class Y> friend class shared_ptr;
#endif
T * px; // contained pointer
detail::weak_count pn; // reference counter
}; // weak_ptr
template<class T, class U> inline bool operator<(weak_ptr<T> const & a, weak_ptr<U> const & b)
{
return a._internal_less(b);
}
template<class T> void swap(weak_ptr<T> & a, weak_ptr<T> & b)
{
a.swap(b);
}
// deprecated, provided for backward compatibility
template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r)
{
return r.lock();
}
} // namespace boost
#ifdef BOOST_MSVC
# pragma warning(pop)
#endif
#endif // #ifndef BOOST_WEAK_PTR_H_INCLUDED
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