//
// weak_ptr.hpp
//
-// Copyright (c) 2001, 2002 Peter Dimov
+// Copyright (c) 2001, 2002, 2003 Peter Dimov
//
-// Permission to copy, use, modify, sell and distribute this software
-// is granted provided this copyright notice appears in all copies.
-// This software is provided "as is" without express or implied
-// warranty, and with no claim as to its suitability for any purpose.
+// 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 <memory> // boost.TR1 include order fix
+#include <boost/detail/shared_count.hpp>
#include <boost/shared_ptr.hpp>
#ifdef BOOST_MSVC // moved here to work around VC++ compiler crash
namespace boost
{
-template<typename T> class weak_ptr
+template<class T> class weak_ptr
{
private:
typedef T element_type;
- weak_ptr(): px(0), pn()
+ weak_ptr(): px(0), pn() // never throws in 1.30+
{
}
// generated copy constructor, assignment, destructor are fine
- template<typename Y>
- weak_ptr(weak_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
+
+//
+// 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<typename Y>
+ 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)
+#if !defined(BOOST_MSVC) || (BOOST_MSVC >= 1300)
- template<typename Y>
+ template<class Y>
weak_ptr & operator=(weak_ptr<Y> const & r) // never throws
{
- px = r.px;
+ px = r.lock().get();
pn = r.pn;
return *this;
}
- template<typename Y>
+ template<class Y>
weak_ptr & operator=(shared_ptr<Y> const & r) // never throws
{
px = r.px;
#endif
- void reset()
+ shared_ptr<T> lock() const // never throws
{
- this_type().swap(*this);
- }
+#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);
- T * get() const // never throws; unsafe in multithreaded programs!
- {
- return pn.use_count() == 0? 0: px;
+#endif
}
long use_count() 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);
}
- bool less(this_type const & rhs) const // implementation detail, never throws
+ void _internal_assign(T * px2, boost::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;
}
private:
- template<typename Y> friend class weak_ptr;
- template<typename Y> friend class shared_ptr;
+ 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
+ T * px; // contained pointer
+ boost::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)
+template<class T, class U> inline bool operator<(weak_ptr<T> const & a, weak_ptr<U> const & b)
{
- return a.get() == b.get();
-}
-
-template<class T, class U> inline bool operator!=(weak_ptr<T> const & a, weak_ptr<U> const & b)
-{
- return a.get() != b.get();
-}
-
-#if __GNUC__ == 2 && __GNUC_MINOR__ <= 96
-
-// Resolve the ambiguity between our op!= and the one in rel_ops
-
-template<typename T> inline bool operator!=(weak_ptr<T> const & a, weak_ptr<T> const & b)
-{
- return a.get() != b.get();
-}
-
-#endif
-
-template<class T> inline bool operator<(weak_ptr<T> const & a, weak_ptr<T> const & b)
-{
- return a.less(b);
+ return a._internal_less(b);
}
template<class T> void swap(weak_ptr<T> & a, weak_ptr<T> & b)
a.swap(b);
}
-template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r) // never throws
+// deprecated, provided for backward compatibility
+template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r)
{
- // optimization: avoid throw overhead
- if(r.use_count() == 0)
- {
- return shared_ptr<T>();
- }
-
- try
- {
- return shared_ptr<T>(r);
- }
- catch(use_count_is_zero const &)
- {
- return shared_ptr<T>();
- }
+ return r.lock();
}
} // namespace boost