Re: smart pointers, slicing, and double deletion

I am seeing some similar problems.  Valgrind is not happy when my objects are destroyed -- I think
the lua_State is getting mucked with after it has closed.  In your case, it is probably the thread's
state that is being altered post-mortem.

One shouldn't have to jump through hoops to do this.  I'm exploring and will let you know if I come
up with anything.

-Evan


Nigel Atkinson wrote:
> Smart pointers, slicing, and double deletion.
> 
> Sound's like a right mess doesn't it.  I finaly cracked it, and since
> I'm sure someone else will come across the same problem I had, I thought
> I'd share.
> 
> What I was trying to do:
> I have a GUI widget (Ogre3d if your wondering), that holds a list of its
> children widgets.  This widget class is the base for several Lua widget
> classes.  I'm using smart pointers to avoid adoption issues.
> 
> Originally using shared pointers, I found that when only C++ had a
> pointer to the instance, it would get 'sliced' if it was a Lua class.
> 
> Bring in shared_ptr_converter.hpp, and that fixes the slicing.  However
> because of part of the way it works, it causes double deletion albeit
> seemingly only at the shut down of a Lua thread. (Its not safe across
> Lua threads either, but that's easily fixed.)
> 
> So to fix the double counting, I started thinking about making my own
> shared pointer - oh man, do I have to? - then realised that
> boost::intrusive_ptr would do most of the job.  Also rather than store
> the counts in the widget class, I just put them in to a map.  Handy for
> debugging.  I still might move that data to the widget class, however
> this would work if you could not change the class.
> 
> So that's the ref counting working now, on to the slicing problem.  I
> added code to my intrusive_ptr_add_ref and intrusive_ptr_release
> functions, to create and remove, a Lua ref i.e. lua_ref(), lua_unref()
> at the appropriate time.  The trick was getting the pointer to the class
> representation on to the Lua stack.  After a bit of following the code
> line by line as my test program made class instances, I found the bit of
> luabind code I needed.
> 
> Attached is my test program, and a Lua script to drive it.  I'd be
> interested in any comments any of you have about it!
> 
> Nigel
> 
> 
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