Re: [g-a-devel]checking Accessible* validity

[Michael Meeks <michael ximian com>]

Hi David,

On Thu, 2002-12-19 at 15:15, David Bolter wrote:
> That should help actually.  I think it could potentially be a good thing 
> for many at-spi clients, but I am not aware of the efficiency costs.

	There is ~0 efficiency cost to emit a slew of 'defunct' events on every
Accessible we have kicking around when the remote app dies - it's a
trivial and (mostly) foolproof thing to do. [ it may not like the
JavaORB depending on how 31337 it is ;-]

> >	Badness ? really ? what sort ? you should be able to reliably invoke
> >these methods in perpetuity without pathalogical failure - ok so you'll
> >get bogus roles [etc.] back, but ...
>
> The example is that gok seg faults (when it tries an Accessible_getName 
> ([accessible for defunct object]);  I am not sure why it seg faults. 
>  Note that the process space for gedit is gone at this point.

	Well - the defunctness of the object should make no difference at all.
This is a bug in gok (or possibly cspi). It sounds like someone is not
ref counting the Accessible * correctly. Now of course - since the same
Accessible * is shared across the whole process ( to make a == b) work
nicely, it's not necessarily at the place you're looking ;-) which may
make things more tricky.

	Are you certain you're not 'taking' a const Accessible * from an event
emission and later un-reffing it ? then again it's prolly a cspi bug ;-)
A stack trace would really help (are you using HEAD at-spi)?

> >	I'm thinking of caching some of the details [ such as role-type ] so we
> >could use that to nicely flag /tag a defunct state perhaps for fast
> >polling.
>
> I think I understand you here, but if the cache is finite then there is 
> still no gaurantees...

	Ah - but we'd cache it by expanding the Accessible* and stashing the
'role' on it - so it'd never expire, and be a nice fast way to poll
individual handles for deadness :-)

> at-poke seems to be working for me...  but does it log events?

	Nope; it doesn't.

> I am still using Accessible_ref and Accessible_unref on the 
> event->source.  I have been on leave for a few months and am a little 
> out of the loop.  Should I be using AccessibleEvent_ref/unref?  Note, I 
> am doubtful that will solve this particular issue.

	It won't solve the immediate issue. I'd recommend trying to binary chop
the problem out and/or auditing all cases of Accessible_unref but first
hack cspi/spi_main.c and #define DEBUG_OBJECTS which stops at-spi from
actually freeing the last ref - if that makes the problem go away - you
know you have a ref counting bug ;-) [ having said that we zap the
structure on free with 0xaa so if you see that value around you also
know ;-]

	HTH,

		Michael.

-- 
 mmeeks gnu org  <><, Pseudo Engineer, itinerant idiot