Re: SMOB tutorial for Scwm and Guile

[Greg Harvey <Greg.Harvey@thezone.net>]

Russ McManus <russell.mcmanus@gs.com> writes:

> > There are currently too many places where you have to have a
> > somewhat intimate knowledge of the inner workings of Guile to get
> > things right (and the lack of documentation doesn't help a bit).
> 
> Other than initializing a smob, can you think of others?  I'd like
> to document the ugly spots, and known work arounds.
> 

There are two that pop to mind right now:

The phantom pointers thing (not Guile's fault, but there should be
some mention of it), where you fetch a pointer to a chunk of data out
of a SCM value and don't use the SCM value again, leading to the
compiler optimizing out the scheme value, and a gc collecting it. You
can get around this using scm_remember(&obj) or
scm_return_first(retval, obj, ...) in the function.

Using scm_must_malloc for storage that can't be reclaimed by the
garbage collector (this mistake happens in the guile code, as
well... it's not necessarily critical, but it's also not a good thing
for the gc to think it's got to handle more memory than it does). This
should really be handled by guile providing a few additional functions
(I've added scm_nonobj_foo, which checks return values and might
signal a gc, but doesn't add this to the total the gc thinks it's
keeping track of). 


-- 
Greg H