GNU bug report logs - #12095
Protecting pointer on bytevector with guardian does not protect memory

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Message #34 received at 12095-done <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: Daniel Hartwig <mandyke <at> gmail.com>
Cc: Patrick Bernaud <patrickb <at> chez.com>, 12095-done <at> debbugs.gnu.org,
	Ian Price <ianprice90 <at> googlemail.com>
Subject: Re: bug#12095: Protecting pointer on bytevector with guardian does
	not protect memory
Date: Mon, 08 Oct 2012 17:42:49 +0200

Daniel Hartwig <mandyke <at> gmail.com> skribis:

> On 8 October 2012 21:44, Ludovic Courtès <ludo <at> gnu.org> wrote:
>>> On 8 October 2012 04:38, Ludovic Courtès <ludo <at> gnu.org> wrote:
>>> Right.  But then the pointer is being collected even though it remains
>>> inside the guardian, in the example it is never extracted from there.
>>
>> Well, when the object reaches the guardian’s zombie list, that’s because
>> it’s been finalized, so any weak references from that object can also be
>> nullified.
>
> Ah.  So I thought that being in the zombie list prevented any
> finalization, thus when the guardian returns an object it is still
> fully functional and only after the reference is lost again does it
> really get finalized.

Well, the object is still usable when the guardian returns it, because
it’s been kept alive by the finalizer (‘finalize_guarded’ in
guardians.c).

Now, whether weak references from the object are subject to
“nullification” by the GC is clearly a gray area, but I’m not surprised
that it is.

>> How does it help?  Should we close the bug?  :-)
>
> Sure.  At least you seem convinced and you has actually hacked on it :-)

Good.  :-)

So closing it now, but feel free to reopen if you think something’s wrong.

Thanks,
Ludo’.

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