From: Andy Wingo <wingo@pobox.com>
To: Mark H Weaver <mhw@netris.org>
Cc: guile-user <guile-user@gnu.org>
Subject: Re: smob mark functions in 2.0
Date: Sat, 27 Sep 2014 17:29:02 +0200 [thread overview]
Message-ID: <87iok92ibl.fsf@pobox.com> (raw)
In-Reply-To: <87tx3vc7d9.fsf@yeeloong.lan> (Mark H. Weaver's message of "Fri, 26 Sep 2014 00:50:58 -0400")
On Fri 26 Sep 2014 06:50, Mark H Weaver <mhw@netris.org> writes:
> Mark H Weaver <mhw@netris.org> writes:
>
>> 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?
This can happen if the object is on a free list. Free lists are just
normal heap-managed data structures -- traced by the GC, counting as
live. See e.g. gc-inline.h in master; a variation of this exact code is
used internally in libgc by the allocation API.
Andy
--
http://wingolog.org/
prev parent reply other threads:[~2014-09-27 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
2014-09-26 4:50 ` Mark H Weaver
2014-09-27 15:29 ` Andy Wingo [this message]
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