[Gnucash-changes] r13152 - gnucash/trunk/lib/libqof/qof - Don't allow the event handler list to shrink while we're traversing it.

[Neil Williams]

On Friday 10 February 2006 10:06 pm, Derek Atkins wrote:
> It's not the best solution.  It /is/ simplistic.  But the problem is
> that the code is re-entrant but it's not quite handling that properly.

OK, that gives me a starting point.

> Hopefully Chris will chime in here.  I honestly don't know offhand
> what crash he's seeing, but it's certainly a theoretical problem due
> to the re-entrancy.

I agree.

> > What about making this stage conditional? (It would at least limit the
> > inexorable growth of the list.)
>
> I'm not sure how you make it conditional.  The real fix is to do
> delayed destruction of the event handler, but then you also need a
> nest calculator to make sure you clean up only at nestlevel 0.  This
> requires at least changing the ABI if not the API 

What about doing that clean up internally?
(at the end of the loop?)

> (I don't recall if 
> the event-handler list is a public QOF object or not).

It's not. Only registering and unregistering event handlers is supported in 
the API. The list is never exposed, there's no foreach or even a count 
available outside QOF.

> Chris, Josh, David, and I had a dicussion about this on IRC before
> Chris made this change (see what you miss by not hanging out on IRC?)

(There was no way I'd have been around at the time that discussion was going 
on. Even allowing for timezones, I wasn't online due to other commitments.)

> Yes, this is a short-term fix to keep the accessing freed memory.
> It's not a long-term fix, which requires a little bit of
> re-architecting the QOF Event code.

OK.

> > This isn't an API issue, it's a technical issue about how best to
> > prevent this crash without causing another elsewhere by consuming
> > resources on a much more limited platform.
>
> It /may/ be an API issue depending on whether the eventlist objects
> are opaque or not.

They are.

> I don't recall and I haven't looked right now. 
> I'll go take a look this evening or this weekend and see if I can come
> up with something.

Thanks.


-- 

Neil Williams
=============
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