1 //////////////////////////////////////////////////////////////////////////////
3 // This file is the adaptation for Interprocess of boost/weak_ptr.hpp
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)
11 // See http://www.boost.org/libs/interprocess for documentation.
13 //////////////////////////////////////////////////////////////////////////////
15 #ifndef BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED
16 #define BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED
18 #ifndef BOOST_CONFIG_HPP
19 # include <boost/config.hpp>
22 #if defined(BOOST_HAS_PRAGMA_ONCE)
26 #include <boost/interprocess/detail/config_begin.hpp>
27 #include <boost/interprocess/detail/workaround.hpp>
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>
37 //!Describes the smart pointer weak_ptr.
40 namespace interprocess{
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.
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.
56 //!weak_ptr operations never throw exceptions.
58 //!The class template is parameterized on T, the type of the object pointed to.
59 template<class T, class A, class D>
62 #if !defined(BOOST_INTERPROCESS_DOXYGEN_INVOKED)
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
71 typedef typename ipcdetail::add_reference
72 <T>::type const_reference;
73 #endif //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED
76 typedef T element_type;
79 //!Effects: Constructs an empty weak_ptr.
80 //!Postconditions: use_count() == 0.
82 : m_pn() // never throws
84 // generated copy constructor, assignment, destructor are fine
86 // The "obvious" converting constructor implementation:
89 // weak_ptr(weak_ptr<Y> const & r): m_px(r.m_px), m_pn(r.m_pn) // never throws
93 // has a serious problem.
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).
98 // It is not possible to avoid spurious access violations since
99 // in multithreaded programs r.m_px may be invalidated at any point.
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.
105 //!Postconditions: use_count() == r.use_count().
109 weak_ptr(weak_ptr<Y, A, D> const & r)
110 : m_pn(r.m_pn) // never throws
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());
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.
122 //!Postconditions: use_count() == r.use_count().
126 weak_ptr(shared_ptr<Y, A, D> const & r)
127 : m_pn(r.m_pn) // never throws
130 //!Effects: Equivalent to weak_ptr(r).swap(*this).
134 //!Notes: The implementation is free to meet the effects (and the
135 //!implied guarantees) via different means, without creating a temporary.
137 weak_ptr & operator=(weak_ptr<Y, A, D> const & r) // never throws
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();
143 m_pn.set_pointer(ref.get());
147 //!Effects: Equivalent to weak_ptr(r).swap(*this).
151 //!Notes: The implementation is free to meet the effects (and the
152 //!implied guarantees) via different means, without creating a temporary.
154 weak_ptr & operator=(shared_ptr<Y, A, D> const & r) // never throws
155 { m_pn = r.m_pn; return *this; }
157 //!Returns: expired()? shared_ptr<T>(): shared_ptr<T>(*this).
160 shared_ptr<T, A, D> lock() const // never throws
162 // optimization: avoid throw overhead
164 return shared_ptr<element_type, A, D>();
167 return shared_ptr<element_type, A, D>(*this);
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>();
177 //!Returns: 0 if *this is empty; otherwise, the number of shared_ptr objects
178 //!that share ownership with *this.
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(); }
187 //!Returns: Returns: use_count() == 0.
191 //!Notes: expired() may be faster than use_count().
192 bool expired() const // never throws
193 { return m_pn.use_count() == 0; }
195 //!Effects: Equivalent to:
196 //!weak_ptr().swap(*this).
197 void reset() // never throws in 1.30+
198 { this_type().swap(*this); }
200 //!Effects: Exchanges the contents of the two
204 void swap(this_type & other) // never throws
205 { ::boost::adl_move_swap(m_pn, other.m_pn); }
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; }
213 void _internal_assign(const ipcdetail::shared_count<Y, A, D> & pn2)
221 template<class T2, class A2, class D2> friend class shared_ptr;
222 template<class T2, class A2, class D2> friend class weak_ptr;
224 ipcdetail::weak_count<T, A, D> m_pn; // reference counter
225 #endif //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED
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); }
232 template<class T, class A, class D> inline
233 void swap(weak_ptr<T, A, D> & a, weak_ptr<T, A, D> & b)
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
245 , typename ManagedMemory::template allocator<void>::type
246 , typename ManagedMemory::template deleter<T>::type
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)
257 return typename managed_weak_ptr<T, ManagedMemory>::type
259 , managed_memory.template get_allocator<void>()
260 , managed_memory.template get_deleter<T>()
264 } // namespace interprocess
267 #include <boost/interprocess/detail/config_end.hpp>
269 #endif // #ifndef BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED