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From: Mark H Weaver <mhw@netris.org>
To: Andy Wingo <wingo@pobox.com>
Cc: guile-user <guile-user@gnu.org>
Subject: Re: smob mark functions in 2.0
Date: Wed, 30 Nov 2011 10:29:26 -0500	[thread overview]
Message-ID: <87fwh5d3xl.fsf@netris.org> (raw)
In-Reply-To: <87aa7mmt76.fsf@pobox.com> (Andy Wingo's message of "Wed, 23 Nov 2011 22:20:45 +0100")

Andy Wingo <wingo@pobox.com> writes:
> Specifically, there is a warning in gc/gc_mark.h:
>
>     /* WARNING: Such a mark procedure may be invoked on an unused object    */
>     /* residing on a free list.  Such objects are cleared, except for a     */
>     /* free list link field in the first word.  Thus mark procedures may    */
>     /* not count on the presence of a type descriptor, and must handle this */
>     /* case correctly somehow.                                              */
>
> So, your mark function might see freed objects.

How can this happen?  If you are marking an object, then presumably it
is still reachable, and therefore the objects it references are also
still reachable.  If any of those reachable objects has been freed,
isn't that already a bug of a different kind?  What am I missing?

   Thanks,
     Mark



  parent reply	other threads:[~2011-11-30 15:29 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-11-23 21:20 smob mark functions in 2.0 Andy Wingo
2011-11-23 23:12 ` Ludovic Courtès
2011-11-24 10:56   ` Andy Wingo
2011-11-24 23:24     ` Ludovic Courtès
2011-11-30 15:29 ` Mark H Weaver [this message]
2014-09-26  4:50   ` Mark H Weaver
2014-09-27 15:29     ` Andy Wingo

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