Re: scm_remember

[Marius Vollmer]

Dirk Herrmann <address@hidden> writes:

> > For example:
> > 
> >     SCM str;
> >     char *chars = SCM_STRING_CHARS (str);
> >     some_syscall (chars);
> >     str = SCM_BOOL_F;
> >     scm_remember (&str);
> > 
> > will ensure that the object originally pointed to by `str' is properly
> > protected, [...]
> 
> Hmmm.  I don't think so.  Why should the original content of str be
> protected in this case?

Because I thought that the compiler will keep the location that holds
the pointer visible to the GC.  I don't know if it is required to do
so.

> You rather protect the new content, namely #f.  In the moment when
> scm_remember (&str) is called, the str object already holds the new
> value, and this is also obvious for the compiler.  Thus, compiler
> _knows_ that &str is a pointer to the value SCM_BOOL_F.

Maybe you are right.  The current method seems to work well in
practice, nevertheless.

> Thus, the implications of scm_remember (&str) are less obvious.  Even
> worse, they are dependent of the compiler's knowledge.

Ok, I think I get it.  Thanks for explaining this so thoroughly!  I
don't feel competent in this issue, and I am pretty much convinced
that you have it right.  I still want to be conservative here.  I
don't see a immediate need to change it, because the current setup
seems to work, so we should proceed carefully.  Anyone else has an
opinion on this?  Maybe you could check with Aubrey?