| ////////////////////////////////////////////////////////////////////////////// |
| // |
| // This file is the adaptation for Interprocess of boost/weak_ptr.hpp |
| // |
| // (C) Copyright Peter Dimov 2001, 2002, 2003 |
| // (C) Copyright Ion Gaztanaga 2006-2009. |
| // Distributed under the Boost Software License, Version 1.0. |
| // (See accompanying file LICENSE_1_0.txt or copy at |
| // http://www.boost.org/LICENSE_1_0.txt) |
| // |
| // See http://www.boost.org/libs/interprocess for documentation. |
| // |
| ////////////////////////////////////////////////////////////////////////////// |
| |
| #ifndef BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED |
| #define BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED |
| |
| #include <boost/interprocess/detail/config_begin.hpp> |
| #include <boost/interprocess/detail/workaround.hpp> |
| |
| #include <boost/interprocess/smart_ptr/shared_ptr.hpp> |
| #include <boost/detail/no_exceptions_support.hpp> |
| #include <boost/interprocess/allocators/allocator.hpp> |
| #include <boost/interprocess/smart_ptr/deleter.hpp> |
| #include <boost/pointer_to_other.hpp> |
| |
| //!\file |
| //!Describes the smart pointer weak_ptr. |
| |
| namespace boost{ |
| namespace interprocess{ |
| |
| //!The weak_ptr class template stores a "weak reference" to an object |
| //!that's already managed by a shared_ptr. To access the object, a weak_ptr |
| //!can be converted to a shared_ptr using the shared_ptr constructor or the |
| //!member function lock. When the last shared_ptr to the object goes away |
| //!and the object is deleted, the attempt to obtain a shared_ptr from the |
| //!weak_ptr instances that refer to the deleted object will fail: the constructor |
| //!will throw an exception of type bad_weak_ptr, and weak_ptr::lock will |
| //!return an empty shared_ptr. |
| //! |
| //!Every weak_ptr meets the CopyConstructible and Assignable requirements |
| //!of the C++ Standard Library, and so can be used in standard library containers. |
| //!Comparison operators are supplied so that weak_ptr works with the standard |
| //!library's associative containers. |
| //! |
| //!weak_ptr operations never throw exceptions. |
| //! |
| //!The class template is parameterized on T, the type of the object pointed to. |
| template<class T, class A, class D> |
| class weak_ptr |
| { |
| /// @cond |
| private: |
| // Borland 5.5.1 specific workarounds |
| typedef weak_ptr<T, A, D> this_type; |
| typedef typename boost::pointer_to_other |
| <typename A::pointer, T>::type pointer; |
| typedef typename detail::add_reference |
| <T>::type reference; |
| typedef typename detail::add_reference |
| <T>::type const_reference; |
| /// @endcond |
| |
| public: |
| typedef T element_type; |
| typedef T value_type; |
| |
| //!Effects: Constructs an empty weak_ptr. |
| //!Postconditions: use_count() == 0. |
| weak_ptr() |
| : m_pn() // never throws |
| {} |
| // generated copy constructor, assignment, destructor are fine |
| // |
| // The "obvious" converting constructor implementation: |
| // |
| // template<class Y> |
| // weak_ptr(weak_ptr<Y> const & r): m_px(r.m_px), m_pn(r.m_pn) // never throws |
| // { |
| // } |
| // |
| // has a serious problem. |
| // |
| // r.m_px may already have been invalidated. The m_px(r.m_px) |
| // conversion may require access to *r.m_px (virtual inheritance). |
| // |
| // It is not possible to avoid spurious access violations since |
| // in multithreaded programs r.m_px may be invalidated at any point. |
| |
| //!Effects: If r is empty, constructs an empty weak_ptr; otherwise, |
| //!constructs a weak_ptr that shares ownership with r as if by storing a |
| //!copy of the pointer stored in r. |
| //! |
| //!Postconditions: use_count() == r.use_count(). |
| //! |
| //!Throws: nothing. |
| template<class Y> |
| weak_ptr(weak_ptr<Y, A, D> const & r) |
| : m_pn(r.m_pn) // never throws |
| { |
| //Construct a temporary shared_ptr so that nobody |
| //can destroy the value while constructing this |
| const shared_ptr<T, A, D> &ref = r.lock(); |
| m_pn.set_pointer(ref.get()); |
| } |
| |
| //!Effects: If r is empty, constructs an empty weak_ptr; otherwise, |
| //!constructs a weak_ptr that shares ownership with r as if by storing a |
| //!copy of the pointer stored in r. |
| //! |
| //!Postconditions: use_count() == r.use_count(). |
| //! |
| //!Throws: nothing. |
| template<class Y> |
| weak_ptr(shared_ptr<Y, A, D> const & r) |
| : m_pn(r.m_pn) // never throws |
| {} |
| |
| //!Effects: Equivalent to weak_ptr(r).swap(*this). |
| //! |
| //!Throws: nothing. |
| //! |
| //!Notes: The implementation is free to meet the effects (and the |
| //!implied guarantees) via different means, without creating a temporary. |
| template<class Y> |
| weak_ptr & operator=(weak_ptr<Y, A, D> const & r) // never throws |
| { |
| //Construct a temporary shared_ptr so that nobody |
| //can destroy the value while constructing this |
| const shared_ptr<T, A, D> &ref = r.lock(); |
| m_pn = r.m_pn; |
| m_pn.set_pointer(ref.get()); |
| return *this; |
| } |
| |
| //!Effects: Equivalent to weak_ptr(r).swap(*this). |
| //! |
| //!Throws: nothing. |
| //! |
| //!Notes: The implementation is free to meet the effects (and the |
| //!implied guarantees) via different means, without creating a temporary. |
| template<class Y> |
| weak_ptr & operator=(shared_ptr<Y, A, D> const & r) // never throws |
| { m_pn = r.m_pn; return *this; } |
| |
| //!Returns: expired()? shared_ptr<T>(): shared_ptr<T>(*this). |
| //! |
| //!Throws: nothing. |
| shared_ptr<T, A, D> lock() const // never throws |
| { |
| // optimization: avoid throw overhead |
| if(expired()){ |
| return shared_ptr<element_type, A, D>(); |
| } |
| BOOST_TRY{ |
| return shared_ptr<element_type, A, D>(*this); |
| } |
| BOOST_CATCH(bad_weak_ptr const &){ |
| // Q: how can we get here? |
| // A: another thread may have invalidated r after the use_count test above. |
| return shared_ptr<element_type, A, D>(); |
| } |
| BOOST_CATCH_END |
| } |
| |
| //!Returns: 0 if *this is empty; otherwise, the number of shared_ptr objects |
| //!that share ownership with *this. |
| //! |
| //!Throws: nothing. |
| //! |
| //!Notes: use_count() is not necessarily efficient. Use only for debugging and |
| //!testing purposes, not for production code. |
| long use_count() const // never throws |
| { return m_pn.use_count(); } |
| |
| //!Returns: Returns: use_count() == 0. |
| //! |
| //!Throws: nothing. |
| //! |
| //!Notes: expired() may be faster than use_count(). |
| bool expired() const // never throws |
| { return m_pn.use_count() == 0; } |
| |
| //!Effects: Equivalent to: |
| //!weak_ptr().swap(*this). |
| void reset() // never throws in 1.30+ |
| { this_type().swap(*this); } |
| |
| //!Effects: Exchanges the contents of the two |
| //!smart pointers. |
| //! |
| //!Throws: nothing. |
| void swap(this_type & other) // never throws |
| { detail::do_swap(m_pn, other.m_pn); } |
| |
| /// @cond |
| template<class T2, class A2, class D2> |
| bool _internal_less(weak_ptr<T2, A2, D2> const & rhs) const |
| { return m_pn < rhs.m_pn; } |
| |
| template<class Y> |
| void _internal_assign(const detail::shared_count<Y, A, D> & pn2) |
| { |
| |
| m_pn = pn2; |
| } |
| |
| private: |
| |
| template<class T2, class A2, class D2> friend class shared_ptr; |
| template<class T2, class A2, class D2> friend class weak_ptr; |
| |
| detail::weak_count<T, A, D> m_pn; // reference counter |
| /// @endcond |
| }; // weak_ptr |
| |
| template<class T, class A, class D, class U, class A2, class D2> inline |
| bool operator<(weak_ptr<T, A, D> const & a, weak_ptr<U, A2, D2> const & b) |
| { return a._internal_less(b); } |
| |
| template<class T, class A, class D> inline |
| void swap(weak_ptr<T, A, D> & a, weak_ptr<T, A, D> & b) |
| { a.swap(b); } |
| |
| //!Returns the type of a weak pointer |
| //!of type T with the allocator boost::interprocess::allocator allocator |
| //!and boost::interprocess::deleter deleter |
| //!that can be constructed in the given managed segment type. |
| template<class T, class ManagedMemory> |
| struct managed_weak_ptr |
| { |
| typedef weak_ptr |
| < T |
| , typename ManagedMemory::template allocator<void>::type |
| , typename ManagedMemory::template deleter<T>::type |
| > type; |
| }; |
| |
| //!Returns an instance of a weak pointer constructed |
| //!with the default allocator and deleter from a pointer |
| //!of type T that has been allocated in the passed managed segment |
| template<class T, class ManagedMemory> |
| inline typename managed_weak_ptr<T, ManagedMemory>::type |
| make_managed_weak_ptr(T *constructed_object, ManagedMemory &managed_memory) |
| { |
| return typename managed_weak_ptr<T, ManagedMemory>::type |
| ( constructed_object |
| , managed_memory.template get_allocator<void>() |
| , managed_memory.template get_deleter<T>() |
| ); |
| } |
| |
| } // namespace interprocess |
| } // namespace boost |
| |
| #include <boost/interprocess/detail/config_end.hpp> |
| |
| #endif // #ifndef BOOST_INTERPROCESS_WEAK_PTR_HPP_INCLUDED |