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Fixed the previous weak_ptr 'fix'.

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[SVN r16370]
This commit is contained in:
Peter Dimov
2002-11-22 14:41:22 +00:00
parent 8d6517484c
commit ea285b4231
1 changed files with 33 additions and 14 deletions
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47
include/boost/weak_ptr.hpp
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@ -16,8 +16,6 @@
#include <boost/shared_ptr.hpp> #include <boost/shared_ptr.hpp>
#include <cstring> // for std::memcpy
#ifdef BOOST_MSVC // moved here to work around VC++ compiler crash #ifdef BOOST_MSVC // moved here to work around VC++ compiler crash
# pragma warning(push) # pragma warning(push)
# pragma warning(disable:4284) // odd return type for operator-> # pragma warning(disable:4284) // odd return type for operator->
@ -26,6 +24,8 @@
namespace boost namespace boost
{ {
template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r); // never throws
template<class T> class weak_ptr template<class T> class weak_ptr
{ {
private: private:
@ -43,12 +43,39 @@ public:
// generated copy constructor, assignment, destructor are fine // generated copy constructor, assignment, destructor are fine
//
// The simple implementation of the converting constructor:
//
// template<class Y>
// weak_ptr(weak_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
// {
// }
//
// has a serious problem.
//
// r.px may already have been invalidated. The px(r.px)
// conversion may require access to *r.px (virtual inheritance).
//
// It is not possible to avoid spurious access violations since
// in multithreaded programs r.px may be invalidated at any point.
//
// A safe conversion between weak_ptr<T> and weak_ptr<Y> must involve
// a temporary shared_ptr.
//
// It is not yet clear whether the converting constructor should be
// present at all, or it's better to require an explicit make_shared call.
//
// The only case for the converting constructor is the weak_ptr<T> -> weak_ptr<cv void>
// conversion.
//
template<class Y> template<class Y>
weak_ptr(weak_ptr<Y> const & r): pn(r.pn) // never throws weak_ptr(weak_ptr<Y> const & r) // never throws
{ {
// r.px may be an invalid pointer value shared_ptr<Y> tmp = make_shared(r);
using namespace std; px = tmp.px;
memcpy(&this->px, &r.px, sizeof(r.px)); pn = tmp.pn;
} }
template<class Y> template<class Y>
@ -58,14 +85,6 @@ public:
#if !defined(BOOST_MSVC) || (BOOST_MSVC > 1200) #if !defined(BOOST_MSVC) || (BOOST_MSVC > 1200)
template<class Y>
weak_ptr & operator=(weak_ptr<Y> const & r) // never throws
{
px = r.px;
pn = r.pn;
return *this;
}
template<class Y> template<class Y>
weak_ptr & operator=(shared_ptr<Y> const & r) // never throws weak_ptr & operator=(shared_ptr<Y> const & r) // never throws
{ {