////////////////////////////////////////////////////////////////////////////// | |
// | |
// 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 |