Should catchlist elements be marked during GC?

Should catchlist elements be marked during GC?

[Kim F. Storm]

During GC, we don't explicitly go through the catchlist, marking the
TAG and VAL member of each element.

I just wondered if it is safe to assume that the TAG and VAL members
are always marked due to some other method?

If not 100% sure, it wouldn't cost a lot to mark them explicitly
during GC.

-- 
Kim F. Storm <storm@cua.dk> http://www.cua.dk

Re: Should catchlist elements be marked during GC?

[Stefan Monnier]

> During GC, we don't explicitly go through the catchlist, marking the
> TAG and VAL member of each element.

What makes you say so?
In Fgarbage_collect I see:

  for (catch = catchlist; catch; catch = catch->next)
    {
      mark_object (catch->tag);
      mark_object (catch->val);
    }

> I just wondered if it is safe to assume that the TAG and VAL members
> are always marked due to some other method?

Actually, it is safe to assume so if we use conservative stack marking
because the catchlist elements are all allocated on the stack, so we
currently mark them redundantly.

The same holds for the handlerlist, the byte stacks, and the backtrace list
(but not for the specpdl array which is not allocated on the stack).

I have a patch to remove this redundant scanning, but keep it for post-22.


        Stefan

Re: Should catchlist elements be marked during GC?

[Kim F. Storm]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> During GC, we don't explicitly go through the catchlist, marking the
>> TAG and VAL member of each element.
>
> What makes you say so?

Since struct catchtag is defined in eval.c, I didn't think alloc.c
would know how to scan the catchlist, so I didn't even bother to check.

> Actually, it is safe to assume so if we use conservative stack marking
> because the catchlist elements are all allocated on the stack, so we
> currently mark them redundantly.

Ah, yes.

-- 
Kim F. Storm <storm@cua.dk> http://www.cua.dk

Re: Should catchlist elements be marked during GC?

[Richard Stallman]

    During GC, we don't explicitly go through the catchlist, marking the
    TAG and VAL member of each element.

Yes we do.  Here's the code from Fgarbage_collect.

  for (catch = catchlist; catch; catch = catch->next)
    {
      mark_object (catch->tag);
      mark_object (catch->val);
    }