272 lines
9.0 KiB
C++
272 lines
9.0 KiB
C++
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//////////////////////////////////////////////////////////////////////////////
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//
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// This file is the adaptation for Interprocess of boost/weak_ptr.hpp
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//
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// (C) Copyright Peter Dimov 2001, 2002, 2003
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// (C) Copyright Ion Gaztanaga 2006-2012.
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// See http://www.boost.org/libs/interprocess for documentation.
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//
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//////////////////////////////////////////////////////////////////////////////
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#ifndef BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED
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#define BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED
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#ifndef BOOST_CONFIG_HPP
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# include <boost/config.hpp>
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#endif
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#
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#if defined(BOOST_HAS_PRAGMA_ONCE)
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# pragma once
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#endif
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#include <boost/interprocess/detail/config_begin.hpp>
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#include <boost/interprocess/detail/workaround.hpp>
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#include <boost/interprocess/smart_ptr/shared_ptr.hpp>
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#include <boost/core/no_exceptions_support.hpp>
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#include <boost/interprocess/allocators/allocator.hpp>
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#include <boost/interprocess/smart_ptr/deleter.hpp>
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#include <boost/intrusive/pointer_traits.hpp>
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#include <boost/move/adl_move_swap.hpp>
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//!\file
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//!Describes the smart pointer weak_ptr.
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namespace boost{
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namespace interprocess{
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//!The weak_ptr class template stores a "weak reference" to an object
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//!that's already managed by a shared_ptr. To access the object, a weak_ptr
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//!can be converted to a shared_ptr using the shared_ptr constructor or the
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//!member function lock. When the last shared_ptr to the object goes away
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//!and the object is deleted, the attempt to obtain a shared_ptr from the
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//!weak_ptr instances that refer to the deleted object will fail: the constructor
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//!will throw an exception of type bad_weak_ptr, and weak_ptr::lock will
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//!return an empty shared_ptr.
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//!
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//!Every weak_ptr meets the CopyConstructible and Assignable requirements
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//!of the C++ Standard Library, and so can be used in standard library containers.
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//!Comparison operators are supplied so that weak_ptr works with the standard
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//!library's associative containers.
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//!
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//!weak_ptr operations never throw exceptions.
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//!
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//!The class template is parameterized on T, the type of the object pointed to.
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template<class T, class A, class D>
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class weak_ptr
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{
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#if !defined(BOOST_INTERPROCESS_DOXYGEN_INVOKED)
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private:
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// Borland 5.5.1 specific workarounds
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typedef weak_ptr<T, A, D> this_type;
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typedef typename boost::container::
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allocator_traits<A>::pointer alloc_ptr;
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typedef typename boost::intrusive::
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pointer_traits<alloc_ptr>::template
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rebind_pointer<T>::type pointer;
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typedef typename ipcdetail::add_reference
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<T>::type reference;
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typedef typename ipcdetail::add_reference
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<T>::type const_reference;
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#endif //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED
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public:
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typedef T element_type;
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typedef T value_type;
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//!Effects: Constructs an empty weak_ptr.
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//!Postconditions: use_count() == 0.
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weak_ptr()
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: m_pn() // never throws
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{}
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// generated copy constructor, assignment, destructor are fine
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//
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// The "obvious" converting constructor implementation:
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//
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// template<class Y>
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// weak_ptr(weak_ptr<Y> const & r): m_px(r.m_px), m_pn(r.m_pn) // never throws
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// {
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// }
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//
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// has a serious problem.
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//
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// r.m_px may already have been invalidated. The m_px(r.m_px)
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// conversion may require access to *r.m_px (virtual inheritance).
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//
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// It is not possible to avoid spurious access violations since
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// in multithreaded programs r.m_px may be invalidated at any point.
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//!Effects: If r is empty, constructs an empty weak_ptr; otherwise,
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//!constructs a weak_ptr that shares ownership with r as if by storing a
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//!copy of the pointer stored in r.
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//!
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//!Postconditions: use_count() == r.use_count().
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//!
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//!Throws: nothing.
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template<class Y>
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weak_ptr(weak_ptr<Y, A, D> const & r)
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: m_pn(r.m_pn) // never throws
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{
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//Construct a temporary shared_ptr so that nobody
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//can destroy the value while constructing this
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const shared_ptr<T, A, D> &ref = r.lock();
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m_pn.set_pointer(ref.get());
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}
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//!Effects: If r is empty, constructs an empty weak_ptr; otherwise,
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//!constructs a weak_ptr that shares ownership with r as if by storing a
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//!copy of the pointer stored in r.
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//!
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//!Postconditions: use_count() == r.use_count().
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//!
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//!Throws: nothing.
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template<class Y>
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weak_ptr(shared_ptr<Y, A, D> const & r)
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: m_pn(r.m_pn) // never throws
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{}
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//!Effects: Equivalent to weak_ptr(r).swap(*this).
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//!
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//!Throws: nothing.
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//!
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//!Notes: The implementation is free to meet the effects (and the
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//!implied guarantees) via different means, without creating a temporary.
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template<class Y>
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weak_ptr & operator=(weak_ptr<Y, A, D> const & r) // never throws
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{
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//Construct a temporary shared_ptr so that nobody
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//can destroy the value while constructing this
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const shared_ptr<T, A, D> &ref = r.lock();
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m_pn = r.m_pn;
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m_pn.set_pointer(ref.get());
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return *this;
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}
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//!Effects: Equivalent to weak_ptr(r).swap(*this).
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//!
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//!Throws: nothing.
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//!
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//!Notes: The implementation is free to meet the effects (and the
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//!implied guarantees) via different means, without creating a temporary.
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template<class Y>
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weak_ptr & operator=(shared_ptr<Y, A, D> const & r) // never throws
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{ m_pn = r.m_pn; return *this; }
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//!Returns: expired()? shared_ptr<T>(): shared_ptr<T>(*this).
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//!
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//!Throws: nothing.
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shared_ptr<T, A, D> lock() const // never throws
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{
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// optimization: avoid throw overhead
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if(expired()){
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return shared_ptr<element_type, A, D>();
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}
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BOOST_TRY{
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return shared_ptr<element_type, A, D>(*this);
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}
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BOOST_CATCH(bad_weak_ptr const &){
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// Q: how can we get here?
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// A: another thread may have invalidated r after the use_count test above.
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return shared_ptr<element_type, A, D>();
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}
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BOOST_CATCH_END
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}
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//!Returns: 0 if *this is empty; otherwise, the number of shared_ptr objects
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//!that share ownership with *this.
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//!
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//!Throws: nothing.
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//!
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//!Notes: use_count() is not necessarily efficient. Use only for debugging and
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//!testing purposes, not for production code.
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long use_count() const // never throws
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{ return m_pn.use_count(); }
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//!Returns: Returns: use_count() == 0.
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//!
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//!Throws: nothing.
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//!
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//!Notes: expired() may be faster than use_count().
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bool expired() const // never throws
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{ return m_pn.use_count() == 0; }
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//!Effects: Equivalent to:
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//!weak_ptr().swap(*this).
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void reset() // never throws in 1.30+
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{ this_type().swap(*this); }
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//!Effects: Exchanges the contents of the two
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//!smart pointers.
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//!
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//!Throws: nothing.
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void swap(this_type & other) // never throws
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{ ::boost::adl_move_swap(m_pn, other.m_pn); }
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#if !defined(BOOST_INTERPROCESS_DOXYGEN_INVOKED)
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template<class T2, class A2, class D2>
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bool _internal_less(weak_ptr<T2, A2, D2> const & rhs) const
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{ return m_pn < rhs.m_pn; }
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template<class Y>
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void _internal_assign(const ipcdetail::shared_count<Y, A, D> & pn2)
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{
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m_pn = pn2;
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}
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private:
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template<class T2, class A2, class D2> friend class shared_ptr;
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template<class T2, class A2, class D2> friend class weak_ptr;
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ipcdetail::weak_count<T, A, D> m_pn; // reference counter
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#endif //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED
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}; // weak_ptr
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template<class T, class A, class D, class U, class A2, class D2> inline
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bool operator<(weak_ptr<T, A, D> const & a, weak_ptr<U, A2, D2> const & b)
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{ return a._internal_less(b); }
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template<class T, class A, class D> inline
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void swap(weak_ptr<T, A, D> & a, weak_ptr<T, A, D> & b)
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{ a.swap(b); }
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//!Returns the type of a weak pointer
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//!of type T with the allocator boost::interprocess::allocator allocator
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//!and boost::interprocess::deleter deleter
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//!that can be constructed in the given managed segment type.
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template<class T, class ManagedMemory>
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struct managed_weak_ptr
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{
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typedef weak_ptr
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< T
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, typename ManagedMemory::template allocator<void>::type
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, typename ManagedMemory::template deleter<T>::type
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> type;
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};
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//!Returns an instance of a weak pointer constructed
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//!with the default allocator and deleter from a pointer
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//!of type T that has been allocated in the passed managed segment
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template<class T, class ManagedMemory>
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inline typename managed_weak_ptr<T, ManagedMemory>::type
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make_managed_weak_ptr(T *constructed_object, ManagedMemory &managed_memory)
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{
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return typename managed_weak_ptr<T, ManagedMemory>::type
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( constructed_object
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, managed_memory.template get_allocator<void>()
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, managed_memory.template get_deleter<T>()
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);
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}
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} // namespace interprocess
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} // namespace boost
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#include <boost/interprocess/detail/config_end.hpp>
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#endif // #ifndef BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED
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