source: NonGTP/Boost/boost/weak_ptr.hpp @ 857

Revision 857, 4.3 KB checked in by igarcia, 19 years ago (diff)
Line 
1#ifndef BOOST_WEAK_PTR_HPP_INCLUDED
2#define BOOST_WEAK_PTR_HPP_INCLUDED
3
4//
5//  weak_ptr.hpp
6//
7//  Copyright (c) 2001, 2002, 2003 Peter Dimov
8//
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)
12//
13//  See http://www.boost.org/libs/smart_ptr/weak_ptr.htm for documentation.
14//
15
16#include <boost/shared_ptr.hpp>
17
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->
21#endif
22
23namespace boost
24{
25
26template<class T> class weak_ptr
27{
28private:
29
30    // Borland 5.5.1 specific workarounds
31    typedef weak_ptr<T> this_type;
32
33public:
34
35    typedef T element_type;
36
37    weak_ptr(): px(0), pn() // never throws in 1.30+
38    {
39    }
40
41//  generated copy constructor, assignment, destructor are fine
42
43
44//
45//  The "obvious" converting constructor implementation:
46//
47//  template<class Y>
48//  weak_ptr(weak_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
49//  {
50//  }
51//
52//  has a serious problem.
53//
54//  r.px may already have been invalidated. The px(r.px)
55//  conversion may require access to *r.px (virtual inheritance).
56//
57//  It is not possible to avoid spurious access violations since
58//  in multithreaded programs r.px may be invalidated at any point.
59//
60
61    template<class Y>
62    weak_ptr(weak_ptr<Y> const & r): pn(r.pn) // never throws
63    {
64        px = r.lock().get();
65    }
66
67    template<class Y>
68    weak_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
69    {
70    }
71
72#if !defined(BOOST_MSVC) || (BOOST_MSVC > 1200)
73
74    template<class Y>
75    weak_ptr & operator=(weak_ptr<Y> const & r) // never throws
76    {
77        px = r.lock().get();
78        pn = r.pn;
79        return *this;
80    }
81
82    template<class Y>
83    weak_ptr & operator=(shared_ptr<Y> const & r) // never throws
84    {
85        px = r.px;
86        pn = r.pn;
87        return *this;
88    }
89
90#endif
91
92    shared_ptr<T> lock() const // never throws
93    {
94#if defined(BOOST_HAS_THREADS)
95
96        // optimization: avoid throw overhead
97        if(expired())
98        {
99            return shared_ptr<element_type>();
100        }
101
102        try
103        {
104            return shared_ptr<element_type>(*this);
105        }
106        catch(bad_weak_ptr const &)
107        {
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>();
111        }
112
113#else
114
115        // optimization: avoid try/catch overhead when single threaded
116        return expired()? shared_ptr<element_type>(): shared_ptr<element_type>(*this);
117
118#endif
119    }
120
121    long use_count() const // never throws
122    {
123        return pn.use_count();
124    }
125
126    bool expired() const // never throws
127    {
128        return pn.use_count() == 0;
129    }
130
131    void reset() // never throws in 1.30+
132    {
133        this_type().swap(*this);
134    }
135
136    void swap(this_type & other) // never throws
137    {
138        std::swap(px, other.px);
139        pn.swap(other.pn);
140    }
141
142    void _internal_assign(T * px2, detail::shared_count const & pn2)
143    {
144        px = px2;
145        pn = pn2;
146    }
147
148    template<class Y> bool _internal_less(weak_ptr<Y> const & rhs) const
149    {
150        return pn < rhs.pn;
151    }
152
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)
155
156#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
157
158private:
159
160    template<class Y> friend class weak_ptr;
161    template<class Y> friend class shared_ptr;
162
163#endif
164
165    T * px;                     // contained pointer
166    detail::weak_count pn;      // reference counter
167
168};  // weak_ptr
169
170template<class T, class U> inline bool operator<(weak_ptr<T> const & a, weak_ptr<U> const & b)
171{
172    return a._internal_less(b);
173}
174
175template<class T> void swap(weak_ptr<T> & a, weak_ptr<T> & b)
176{
177    a.swap(b);
178}
179
180// deprecated, provided for backward compatibility
181template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r)
182{
183    return r.lock();
184}
185
186} // namespace boost
187
188#ifdef BOOST_MSVC
189# pragma warning(pop)
190#endif   
191
192#endif  // #ifndef BOOST_WEAK_PTR_HPP_INCLUDED
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