1 #ifndef BOOST_WEAK_PTR_HPP_INCLUDED
2 #define BOOST_WEAK_PTR_HPP_INCLUDED
7 // Copyright (c) 2001, 2002, 2003 Peter Dimov
9 // Distributed under the Boost Software License, Version 1.0. (See
10 // accompanying file LICENSE_1_0.txt or copy at
11 // http://www.boost.org/LICENSE_1_0.txt)
13 // See http://www.boost.org/libs/smart_ptr/weak_ptr.htm for documentation.
16 #include <boost/shared_ptr.hpp>
18 #ifdef BOOST_MSVC // moved here to work around VC++ compiler crash
19 # pragma warning(push)
20 # pragma warning(disable:4284) // odd return type for operator->
26 template<class T> class weak_ptr
30 // Borland 5.5.1 specific workarounds
31 typedef weak_ptr<T> this_type;
35 typedef T element_type;
37 weak_ptr(): px(0), pn() // never throws in 1.30+
41 // generated copy constructor, assignment, destructor are fine
45 // The "obvious" converting constructor implementation:
48 // weak_ptr(weak_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
52 // has a serious problem.
54 // r.px may already have been invalidated. The px(r.px)
55 // conversion may require access to *r.px (virtual inheritance).
57 // It is not possible to avoid spurious access violations since
58 // in multithreaded programs r.px may be invalidated at any point.
62 weak_ptr(weak_ptr<Y> const & r): pn(r.pn) // never throws
68 weak_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
72 #if !defined(BOOST_MSVC) || (BOOST_MSVC > 1200)
75 weak_ptr & operator=(weak_ptr<Y> const & r) // never throws
83 weak_ptr & operator=(shared_ptr<Y> const & r) // never throws
92 shared_ptr<T> lock() const // never throws
94 #if defined(BOOST_HAS_THREADS)
96 // optimization: avoid throw overhead
99 return shared_ptr<element_type>();
104 return shared_ptr<element_type>(*this);
106 catch(bad_weak_ptr const &)
108 // Q: how can we get here?
109 // A: another thread may have invalidated r after the use_count test above.
110 return shared_ptr<element_type>();
115 // optimization: avoid try/catch overhead when single threaded
116 return expired()? shared_ptr<element_type>(): shared_ptr<element_type>(*this);
121 long use_count() const // never throws
123 return pn.use_count();
126 bool expired() const // never throws
128 return pn.use_count() == 0;
131 void reset() // never throws in 1.30+
133 this_type().swap(*this);
136 void swap(this_type & other) // never throws
138 std::swap(px, other.px);
142 void _internal_assign(T * px2, detail::shared_count const & pn2)
148 template<class Y> bool _internal_less(weak_ptr<Y> const & rhs) const
153 // Tasteless as this may seem, making all members public allows member templates
154 // to work in the absence of member template friends. (Matthew Langston)
156 #ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
160 template<class Y> friend class weak_ptr;
161 template<class Y> friend class shared_ptr;
165 T * px; // contained pointer
166 detail::weak_count pn; // reference counter
170 template<class T, class U> inline bool operator<(weak_ptr<T> const & a, weak_ptr<U> const & b)
172 return a._internal_less(b);
175 template<class T> void swap(weak_ptr<T> & a, weak_ptr<T> & b)
180 // deprecated, provided for backward compatibility
181 template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r)
189 # pragma warning(pop)
192 #endif // #ifndef BOOST_WEAK_PTR_HPP_INCLUDED