Re: gh_enter reconsidered

[Jim Blandy <jimb@red-bean.com>]

In the absence of really exciting new hacks I haven't heard of, Guile
will continue to use conservative GC.  The alternatives --- explicitly
marking heap pointers, and reference counting --- are clearly
unacceptable, given Guile's goals.  I have direct long-term experience
trying to use the first, and the second doesn't support Scheme's
semantics.

I think nobody's done a library for finding the stack base, because
nobody but a conservative GC would care.  Conservative GC's are
relatively new.

I definitely sympathize with Guido's reaction --- Why would I put
something that unportable in my interpreter? --- but I think it's
better than reference counting.

It's okay to introduce horrible, system-specific hacks like this, if
they have a clean interface --- that is, if they don't percolate their
inner details out to the rest of the system.  On the face of it, I
think finding the stack bottom falls in this category.