GNU bug report logs - #9581
24.0.50; dbus-unregister-object fails if service is nil

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Julien Danjou <julien <at> danjou.info>
Subject: bug#9581: closed (Re: bug#9581: 24.0.50; dbus-unregister-object
 fails if service is nil)
Date: Mon, 26 Sep 2011 13:59:02 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#9581: 24.0.50; dbus-unregister-object fails if service is nil

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 9581 <at> debbugs.gnu.org.

-- 
9581: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=9581
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Michael Albinus <michael.albinus <at> gmx.de>
To: Julien Danjou <julien <at> danjou.info>
Cc: 9581-done <at> debbugs.gnu.org
Subject: Re: bug#9581: 24.0.50; dbus-unregister-object fails if service is nil
Date: Mon, 26 Sep 2011 15:57:57 +0200

Julien Danjou <julien <at> danjou.info> writes:

> I think you can close this bug, and maybe reopen one if you want to
> track the other changes you want to do after the pretest. You call. :)

OK, closed.

I don't believe we need another bug report just to remind myself ... I
tend to forget everything (ask my wife!), but this patch is already
prepared in my local repo. I should find it after the release.

Thanks for your patient testing, and best regards, Michael.

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From: Julien Danjou <julien <at> danjou.info>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.0.50; dbus-unregister-object fails if service is nil
Date: Fri, 23 Sep 2011 01:01:17 +0200

If you use `dbus-register-signal' with a nil SERVICE value, like:

      (dbus-register-signal :session nil
                            "/org/gtk/Private/RemoteVolumeMonitor"
                            "org.gtk.Private.RemoteVolumeMonitor" "VolumeAdded"
                            'identity)

This is valid and works fine. However, on unregister it fails:
Debugger entered--Lisp error: (dbus-error "Call to ReleaseName has wrong args (b, expected s)")
  dbus-call-method(:session "org.freedesktop.DBus" "/org/freedesktop/DBus" "org.freedesktop.DBus" "ReleaseName" nil)
  dbus-unregister-object(((:session "org.gtk.Private.RemoteVolumeMonitor" "VolumeAdded") (nil "/org/gtk/Private/RemoteVolumeMonitor" identity)))

Why does it fail? Because of the following code in
`dbus-unregister-object':

#+begin_src emacs-lisp
	(unless found
	  (dbus-call-method
	   bus dbus-service-dbus dbus-path-dbus dbus-interface-dbus
	   "ReleaseName" service))))
+end_src

And here service is… nil. Which is translated to a boolean (b) but
should be a string (s).

But honestly, I'm not sure what the good fix is. To me, this code is
totally wrong in such a case.

When using `dbus-register-signal', this happens:
1. the dbus_bus_add_match() function is called to add a match on the bus
2. the (match callback) pair is recorded into
   `dbus-registered-objets-table' 

This makes things work. When a signal happens, something is looking into
`dbus-registered-objets-table' and call the callback function.

But to stop listening for a signal, the function to use is
`dbus-unregister-object', and it is doing this:
1. remove the (match callback) pair from `dbus-registered-objets-table'
2. call ReleaseName on the service we were listening

While I agree on point 1., the point 2. is totally irrelevant in such a
case. There's no need to do such a thing, the name has never been
requested with RequestName before.

I think that:
- step 2 should be removed or another function should be created which
  does not send a ReleaseName
- dbus_bus_remove_match() should be used to remove the watch from the
  bus, which would be a lot cleaner.

-- 
Julien Danjou

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