Re: smart pointers, slicing, and double deletion

I also would like your approach if it is possible and easy to maintain.
But how about making C++ side control all the memory
allocation/deallocation?

For example, in lua part, only widget names are stored, and every time a
pointer is needed, you use an interface function to check and retrieve if
such widget exists.

Taesoo

On Wed, Nov 25, 2009 at 8:23 AM, Nigel Atkinson <[email protected]>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
>
>
> ------------------------------------------------------------------------------
> Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
> trial. Simplify your report design, integration and deployment - and focus
> on
> what you do best, core application coding. Discover what's new with
> Crystal Reports now.  http://p.sf.net/sfu/bobj-july
> _______________________________________________
> luabind-user mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/luabind-user
>
>

------------------------------------------------------------------------------
Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day 
trial. Simplify your report design, integration and deployment - and focus on 
what you do best, core application coding. Discover what's new with
Crystal Reports now.  http://p.sf.net/sfu/bobj-july

_______________________________________________
luabind-user mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/luabind-user