Re: [Denemo-devel] scm_dynwinds etc. [was:] Midi shortcuts

[Richard Shann]

On Wed, 2011-05-11 at 15:54 +0200, R. Mattes wrote:
> On Wed, 11 May 2011 08:15:41 -0500, Jeremiah Benham wrote
> > >
> > > Jeremiah - do you have time to pick this up again, the tidying up of  
> > > the
> > > memory leaks in view.c scheme stuff?
> > 
> > Yes. I have some time to do that. I am a bit confused as to what I  
> > need to do now. I'll read over this thread a few more times and ask  
> > some questions perhaps.
> 
> I think the general approach should be:
> 
> * There _are_ situations where scm_dynwind-protection is needed.
>  All calls
>   into scheme while resources are temporarily allocated need to be protected
>   by setting up a dynwind context _and registering all cleanups with that 
>   context_. [Note: very confusing: atm there are calls to scm_dynwind_end
>   in functions that don't call scm_dynwind_begin. That's asking for trouble 
> ...)
> 
> * Functions that _don't_ call into scheme or that call scheme while there is
>   no chance of non-local exits should clean up their locally allocated 
> resources
>   themself.
In practice this just means removing all the scm_dynwind stuff that you
did, as we don't do any non-local jumps from scheme. Instead free any C
strings created with scm_to_locale_string() using free() (not g_free()).

 More importantly the scm_take_from... need to revert to scm_from... in
all cases. In the cases where the string being passed is freshly
allocated (ie g_malloc'd) then call g_free() on it having created the
scm_from... SCM structure. We can't exploit scm_take_from... (as I
previously suggested) because it calls free() and glib  is using its own
memory allocator (so g_free() doesn't call free()). (So, another wild
goose chase started by me I'm afraid :(

It is only not crashing at the moment, because it seems scheme is not
collecting its garbage...

Richard



> 
> BTW, just a comment on style: while a macro like SCM2LSTRING seems like a good
> idea
> to save a few keystrokes it's very tempting to write something like:
> 
>  scm_dynwind_begin();
>  char* my_string = SCM2LSTRING(a_scn_val);
>  ....
> 
>  scm_dynwind_end();
> 
>  ...
> 
>  char* foo = my_string;
> 
> 
> More questions?
> 
>  Cheers, RalfD
> 
> 
> --
> R. Mattes -
> Hochschule fuer Musik Freiburg
> address@hidden
>