Re: segfault when get_pointer returns null

Yes, I saw your ward_ptr, when I browsed through the previous entries.
Actually I was inspired by it. In my server however I have very precise
control over where and how the objects in question are created and
destroyed. So to prevent rewriting the server and wrapping all pointers
of the required types into ward_ptrs because invalidate() would need to
be called outside lua (scripters should have no access to destroying
e.g. players), I was looking for a simpler approach in terms of
usability, where I just need to wrap those pointers when they get passed
to lua.
Of course, when I throw the appropriate exception in get() everything
works just fine. Thanks for helping (again, I should say).

Andreas


Am Montag, den 28.02.2011, 11:02 +1100 schrieb Nigel Atkinson:
> I had a similar problem with pointers to things created and destroyed by
> C++ code, but held in Lua. i.e.
> 
> thingy = CreateThingy()
> ...
> ...
> DestroyThingy( thingy )
> 
> --Accidently use pointer later on...
> thingy:method()  // Boom!
> 
> I solved this with the following code:
> https://github.com/merlinblack/Game-Engine-Testbed/blob/master/include/ward_ptr.h
> 
> and some glue functions..
> 
> void DestroyThingy( ward_ptr ptr )
> {
>   RealDestroyThingy( ptr.get() );
>   ptr.invalidate();
> }
> 
> 
> On Sun, February 27, 2011 9:57 am, Andreas Grob wrote:
> > Hello all,
> >
> > right now I am trying to write a wrapping pointer to hold objects passed
> > to luabind. The idea is to change the behaviour of get_pointer at
> > runtime to invalidate objects.
> > While I can wrap null pointers and receive luabind::error upon trying to
> > call a member, the program segfaults in luabind when I change the result
> > of get_pointer from a normal pointer to null at a later time, i.e. after
> > passing the wrapped object to luabind.
> >
> > Here is the stacktrace when get_pointer just returned null before the
> > segfault:
> >
> > #0  luabind::detail::pointer_holder<fuse_ptr<myclass>, void const>::get
> > (this=0x805b630, target=3)
> >     at /usr/include/luabind/detail/instance_holder.hpp:100
> > #1  0x0804bd60 in luabind::detail::object_rep::get_instance
> > (this=0x805b62c, target=3)
> >     at /usr/include/luabind/detail/object_rep.hpp:59
> > #2  0x0804f99a in luabind::detail::ref_converter::match<myclass>
> > (this=0xbfffee94, L=0x80550a8, index=1)
> >     at /usr/include/luabind/detail/policy.hpp:402
> > #3  0x0804f776 in luabind::detail::invoke_member<void (myclass::*)(),
> > boost::mpl::vector2<void, myclass&>, luabind::detail::null_type>
> > (L=0x80550a8, self=..., ctx=..., f=@0x805a5b8)
> > at /usr/include/luabind/detail/call.hpp:257
> > #4  0x0804f6d3 in luabind::detail::invoke0<void (myclass::*)(),
> > boost::mpl::vector2<void, myclass&>, luabind::detail::null_type,
> > boost::is_void<void> > (L=0x80550a8, self=..., ctx=..., f=@0x805a5b8,
> > policies=...) at /usr/include/luabind/detail/call.hpp:78
> > #5  0x0804f698 in luabind::detail::invoke<void (myclass::*)(),
> > boost::mpl::vector2<void, myclass&>, luabind::detail::null_type> (
> >     L=0x80550a8, self=..., ctx=..., f=@0x805a5b8, policies=...)
> > at /usr/include/luabind/detail/call.hpp:101
> > #6  0x0804f5d6 in luabind::detail::function_object_impl<void
> > (myclass::*)(), boost::mpl::vector2<void, myclass&>,
> > luabind::detail::null_type>::entry_point (L=0x80550a8)
> > at /usr/include/luabind/make_function.hpp:62
> > [...calls from lua...]
> >
> > If continued it segfaults in frame 3, line 287:
> > (c0.apply(L, LUABIND_DECORATE_TYPE(a0), index0).*f)(
> >
> >
> > My question is: Why is the call to a member of null not detected and an
> > exception thrown?
> >
> > The code is attached (using lua 5.1.4 and luabind 0.9.1).
> >
> > Thank you very much.
> >
> > Best regards,
> > Andreas
> >
> >
> >
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> 
> 
> 
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Real-Time with Splunk. Collect, index and harness all the fast moving IT data 
generated by your applications, servers and devices whether physical, virtual
or in the cloud. Deliver compliance at lower cost and gain new business 
insights. http://p.sf.net/sfu/splunk-dev2dev