Re: [g-a-devel]leaked objects - basic reference counting tutorial

[David Bolter <david bolter utoronto ca>]

Michael Meeks wrote:

> On Mon, 2002-07-22 at 11:02, David Bolter wrote:
>
> > i get a whole bunch of leaked object output messages in the terminal 
> > which launched the gok.
>
> 	Ok; these are signs of gok not doing correct reference counting.
Okay, I wanted to be sure this was the cause - thanks!

> > leaked object gedit, role invalid
>
> 	So - someone took a ref on the gedit toplevel application object and
> didn't release it.
>
> 	To release a reference you need to do:
>
> 	Accessible_unref (my_ref);
If my call to Accessible_unref reduces the ref count for that object to 
0, is it immediately removed from the hash table?

> 	You have to take a reference if you want to keep a reference beyond the
> lifetime of the callback you took it in [ if in a callback ], ie. this
> is wrong:
Right, okay - just for events  I may need to ref...  (I think I was also 
added a ref for interrogated accessibles - tsk tsk).

Thanks again Michael, for the info, and the patch.

cheers,

~~David

> static Accessible *acc = NULL;
> void my_event_callback (AccessibleEvent *e)
> {
> 	acc = e->source;		/* WRONG */
> }
>
> 	Since as soon as the method quits acc will be left pointing at an
> accessible that we don't own a reference on so, instead we must do:
>
> void my_event_callback (AccessibleEvent *e)
> {
> 	Accessible_unref (acc);
> 	acc = e->source;
> 	Accessible_ref (acc);           /* RIGHT */
> }
>
> 	I think (owing to the miracle of rushed API design) that you can't do
> the obvious:
>
> 	acc = Accessible_ref (e->source);
>
> 	which would be far superior.
>
> 	That's for callbacks; for methods:
>
> AccessibleText *a = Accessible_getText (acc);
>
> 	returns a reference - indeed, any method that returns an Accessible,
> returns a reference to it; thus you have to unref it later, or it is
> leaked thus:
>
> AccessibleText *a = Accessible_getText (acc);
> ... do something with it ...
> Accessible_unref (a);
>
> 	Finally it would be best if the code actually told you how many refs
> were leaked, otherwise it's going to be difficult to see you making any
> progress eliminating them [ which can only really be done by code
> reading ]: I'd add this patch:
>
> 	[ extraordinary to put brackets round a ? conditional expr ]
>
> 	
> Index: spi_main.c
> ===================================================================
> RCS file: /cvs/gnome/at-spi/cspi/spi_main.c,v
> retrieving revision 1.26
> diff -u -p -u -r1.26 spi_main.c
> --- spi_main.c	20 Jun 2002 12:10:34 -0000	1.26
> +++ spi_main.c	23 Jul 2002 15:00:57 -0000
> @@ -378,9 +378,10 @@ report_leaked_ref (gpointer key, gpointe
> 	if (cspi_exception ()) name = NULL;
> 	role = Accessible_getRoleName (a);
> 	if (cspi_exception ()) role = NULL;
> -	fprintf (stderr, "leaked object %s, role %s\n", (name) ? name : "<?>",
> -		 (role) ? role : "<?>");
> -	if (name) SPI_freeString (name);
> +	fprintf (stderr, "leaked %d references to object %s, role %s\n",
> +		 a->ref_count, name ? name : "<?>", role ? role : "<?>");
> +	if (name)
> +		SPI_freeString (name);
> }
>
> 	Finally - leaks are worth fixing, since otherwise the app at the other
> end will eventually run out of resources, which you are keeping alive by
> holding references to - perhaps to objects that no-longer have peers
> that exist.
>
> 	Bill - can I commit the above [ and fix a warning in cspi/bonobo that's
> annoying me ? ]
>
> 	Regards,
>
> 		Michael.