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1 | ////////////////////////////////////////////////////////////////////////////// |
2 | // | |
3 | // This file is the adaptation for Interprocess of boost/weak_ptr.hpp | |
4 | // | |
5 | // (C) Copyright Peter Dimov 2001, 2002, 2003 | |
6 | // (C) Copyright Ion Gaztanaga 2006-2012. | |
7 | // Distributed under the Boost Software License, Version 1.0. | |
8 | // (See accompanying file LICENSE_1_0.txt or copy at | |
9 | // http://www.boost.org/LICENSE_1_0.txt) | |
10 | // | |
11 | // See http://www.boost.org/libs/interprocess for documentation. | |
12 | // | |
13 | ////////////////////////////////////////////////////////////////////////////// | |
14 | ||
15 | #ifndef BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED | |
16 | #define BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED | |
17 | ||
18 | #ifndef BOOST_CONFIG_HPP | |
19 | # include <boost/config.hpp> | |
20 | #endif | |
21 | # | |
22 | #if defined(BOOST_HAS_PRAGMA_ONCE) | |
23 | # pragma once | |
24 | #endif | |
25 | ||
26 | #include <boost/interprocess/detail/config_begin.hpp> | |
27 | #include <boost/interprocess/detail/workaround.hpp> | |
28 | ||
29 | #include <boost/interprocess/smart_ptr/shared_ptr.hpp> | |
30 | #include <boost/core/no_exceptions_support.hpp> | |
31 | #include <boost/interprocess/allocators/allocator.hpp> | |
32 | #include <boost/interprocess/smart_ptr/deleter.hpp> | |
33 | #include <boost/intrusive/pointer_traits.hpp> | |
34 | #include <boost/move/adl_move_swap.hpp> | |
35 | ||
36 | //!\file | |
37 | //!Describes the smart pointer weak_ptr. | |
38 | ||
39 | namespace boost{ | |
40 | namespace interprocess{ | |
41 | ||
42 | //!The weak_ptr class template stores a "weak reference" to an object | |
43 | //!that's already managed by a shared_ptr. To access the object, a weak_ptr | |
44 | //!can be converted to a shared_ptr using the shared_ptr constructor or the | |
45 | //!member function lock. When the last shared_ptr to the object goes away | |
46 | //!and the object is deleted, the attempt to obtain a shared_ptr from the | |
47 | //!weak_ptr instances that refer to the deleted object will fail: the constructor | |
48 | //!will throw an exception of type bad_weak_ptr, and weak_ptr::lock will | |
49 | //!return an empty shared_ptr. | |
50 | //! | |
51 | //!Every weak_ptr meets the CopyConstructible and Assignable requirements | |
52 | //!of the C++ Standard Library, and so can be used in standard library containers. | |
53 | //!Comparison operators are supplied so that weak_ptr works with the standard | |
54 | //!library's associative containers. | |
55 | //! | |
56 | //!weak_ptr operations never throw exceptions. | |
57 | //! | |
58 | //!The class template is parameterized on T, the type of the object pointed to. | |
59 | template<class T, class A, class D> | |
60 | class weak_ptr | |
61 | { | |
62 | #if !defined(BOOST_INTERPROCESS_DOXYGEN_INVOKED) | |
63 | private: | |
64 | // Borland 5.5.1 specific workarounds | |
65 | typedef weak_ptr<T, A, D> this_type; | |
66 | typedef typename boost::intrusive:: | |
67 | pointer_traits<typename A::pointer>::template | |
68 | rebind_pointer<T>::type pointer; | |
69 | typedef typename ipcdetail::add_reference | |
70 | <T>::type reference; | |
71 | typedef typename ipcdetail::add_reference | |
72 | <T>::type const_reference; | |
73 | #endif //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED | |
74 | ||
75 | public: | |
76 | typedef T element_type; | |
77 | typedef T value_type; | |
78 | ||
79 | //!Effects: Constructs an empty weak_ptr. | |
80 | //!Postconditions: use_count() == 0. | |
81 | weak_ptr() | |
82 | : m_pn() // never throws | |
83 | {} | |
84 | // generated copy constructor, assignment, destructor are fine | |
85 | // | |
86 | // The "obvious" converting constructor implementation: | |
87 | // | |
88 | // template<class Y> | |
89 | // weak_ptr(weak_ptr<Y> const & r): m_px(r.m_px), m_pn(r.m_pn) // never throws | |
90 | // { | |
91 | // } | |
92 | // | |
93 | // has a serious problem. | |
94 | // | |
95 | // r.m_px may already have been invalidated. The m_px(r.m_px) | |
96 | // conversion may require access to *r.m_px (virtual inheritance). | |
97 | // | |
98 | // It is not possible to avoid spurious access violations since | |
99 | // in multithreaded programs r.m_px may be invalidated at any point. | |
100 | ||
101 | //!Effects: If r is empty, constructs an empty weak_ptr; otherwise, | |
102 | //!constructs a weak_ptr that shares ownership with r as if by storing a | |
103 | //!copy of the pointer stored in r. | |
104 | //! | |
105 | //!Postconditions: use_count() == r.use_count(). | |
106 | //! | |
107 | //!Throws: nothing. | |
108 | template<class Y> | |
109 | weak_ptr(weak_ptr<Y, A, D> const & r) | |
110 | : m_pn(r.m_pn) // never throws | |
111 | { | |
112 | //Construct a temporary shared_ptr so that nobody | |
113 | //can destroy the value while constructing this | |
114 | const shared_ptr<T, A, D> &ref = r.lock(); | |
115 | m_pn.set_pointer(ref.get()); | |
116 | } | |
117 | ||
118 | //!Effects: If r is empty, constructs an empty weak_ptr; otherwise, | |
119 | //!constructs a weak_ptr that shares ownership with r as if by storing a | |
120 | //!copy of the pointer stored in r. | |
121 | //! | |
122 | //!Postconditions: use_count() == r.use_count(). | |
123 | //! | |
124 | //!Throws: nothing. | |
125 | template<class Y> | |
126 | weak_ptr(shared_ptr<Y, A, D> const & r) | |
127 | : m_pn(r.m_pn) // never throws | |
128 | {} | |
129 | ||
130 | //!Effects: Equivalent to weak_ptr(r).swap(*this). | |
131 | //! | |
132 | //!Throws: nothing. | |
133 | //! | |
134 | //!Notes: The implementation is free to meet the effects (and the | |
135 | //!implied guarantees) via different means, without creating a temporary. | |
136 | template<class Y> | |
137 | weak_ptr & operator=(weak_ptr<Y, A, D> const & r) // never throws | |
138 | { | |
139 | //Construct a temporary shared_ptr so that nobody | |
140 | //can destroy the value while constructing this | |
141 | const shared_ptr<T, A, D> &ref = r.lock(); | |
142 | m_pn = r.m_pn; | |
143 | m_pn.set_pointer(ref.get()); | |
144 | return *this; | |
145 | } | |
146 | ||
147 | //!Effects: Equivalent to weak_ptr(r).swap(*this). | |
148 | //! | |
149 | //!Throws: nothing. | |
150 | //! | |
151 | //!Notes: The implementation is free to meet the effects (and the | |
152 | //!implied guarantees) via different means, without creating a temporary. | |
153 | template<class Y> | |
154 | weak_ptr & operator=(shared_ptr<Y, A, D> const & r) // never throws | |
155 | { m_pn = r.m_pn; return *this; } | |
156 | ||
157 | //!Returns: expired()? shared_ptr<T>(): shared_ptr<T>(*this). | |
158 | //! | |
159 | //!Throws: nothing. | |
160 | shared_ptr<T, A, D> lock() const // never throws | |
161 | { | |
162 | // optimization: avoid throw overhead | |
163 | if(expired()){ | |
164 | return shared_ptr<element_type, A, D>(); | |
165 | } | |
166 | BOOST_TRY{ | |
167 | return shared_ptr<element_type, A, D>(*this); | |
168 | } | |
169 | BOOST_CATCH(bad_weak_ptr const &){ | |
170 | // Q: how can we get here? | |
171 | // A: another thread may have invalidated r after the use_count test above. | |
172 | return shared_ptr<element_type, A, D>(); | |
173 | } | |
174 | BOOST_CATCH_END | |
175 | } | |
176 | ||
177 | //!Returns: 0 if *this is empty; otherwise, the number of shared_ptr objects | |
178 | //!that share ownership with *this. | |
179 | //! | |
180 | //!Throws: nothing. | |
181 | //! | |
182 | //!Notes: use_count() is not necessarily efficient. Use only for debugging and | |
183 | //!testing purposes, not for production code. | |
184 | long use_count() const // never throws | |
185 | { return m_pn.use_count(); } | |
186 | ||
187 | //!Returns: Returns: use_count() == 0. | |
188 | //! | |
189 | //!Throws: nothing. | |
190 | //! | |
191 | //!Notes: expired() may be faster than use_count(). | |
192 | bool expired() const // never throws | |
193 | { return m_pn.use_count() == 0; } | |
194 | ||
195 | //!Effects: Equivalent to: | |
196 | //!weak_ptr().swap(*this). | |
197 | void reset() // never throws in 1.30+ | |
198 | { this_type().swap(*this); } | |
199 | ||
200 | //!Effects: Exchanges the contents of the two | |
201 | //!smart pointers. | |
202 | //! | |
203 | //!Throws: nothing. | |
204 | void swap(this_type & other) // never throws | |
205 | { ::boost::adl_move_swap(m_pn, other.m_pn); } | |
206 | ||
207 | #if !defined(BOOST_INTERPROCESS_DOXYGEN_INVOKED) | |
208 | template<class T2, class A2, class D2> | |
209 | bool _internal_less(weak_ptr<T2, A2, D2> const & rhs) const | |
210 | { return m_pn < rhs.m_pn; } | |
211 | ||
212 | template<class Y> | |
213 | void _internal_assign(const ipcdetail::shared_count<Y, A, D> & pn2) | |
214 | { | |
215 | ||
216 | m_pn = pn2; | |
217 | } | |
218 | ||
219 | private: | |
220 | ||
221 | template<class T2, class A2, class D2> friend class shared_ptr; | |
222 | template<class T2, class A2, class D2> friend class weak_ptr; | |
223 | ||
224 | ipcdetail::weak_count<T, A, D> m_pn; // reference counter | |
225 | #endif //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED | |
226 | }; // weak_ptr | |
227 | ||
228 | template<class T, class A, class D, class U, class A2, class D2> inline | |
229 | bool operator<(weak_ptr<T, A, D> const & a, weak_ptr<U, A2, D2> const & b) | |
230 | { return a._internal_less(b); } | |
231 | ||
232 | template<class T, class A, class D> inline | |
233 | void swap(weak_ptr<T, A, D> & a, weak_ptr<T, A, D> & b) | |
234 | { a.swap(b); } | |
235 | ||
236 | //!Returns the type of a weak pointer | |
237 | //!of type T with the allocator boost::interprocess::allocator allocator | |
238 | //!and boost::interprocess::deleter deleter | |
239 | //!that can be constructed in the given managed segment type. | |
240 | template<class T, class ManagedMemory> | |
241 | struct managed_weak_ptr | |
242 | { | |
243 | typedef weak_ptr | |
244 | < T | |
245 | , typename ManagedMemory::template allocator<void>::type | |
246 | , typename ManagedMemory::template deleter<T>::type | |
247 | > type; | |
248 | }; | |
249 | ||
250 | //!Returns an instance of a weak pointer constructed | |
251 | //!with the default allocator and deleter from a pointer | |
252 | //!of type T that has been allocated in the passed managed segment | |
253 | template<class T, class ManagedMemory> | |
254 | inline typename managed_weak_ptr<T, ManagedMemory>::type | |
255 | make_managed_weak_ptr(T *constructed_object, ManagedMemory &managed_memory) | |
256 | { | |
257 | return typename managed_weak_ptr<T, ManagedMemory>::type | |
258 | ( constructed_object | |
259 | , managed_memory.template get_allocator<void>() | |
260 | , managed_memory.template get_deleter<T>() | |
261 | ); | |
262 | } | |
263 | ||
264 | } // namespace interprocess | |
265 | } // namespace boost | |
266 | ||
267 | #include <boost/interprocess/detail/config_end.hpp> | |
268 | ||
269 | #endif // #ifndef BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED |