Re: Emacs and DBUS

[Michael Albinus <michael dot albinus at gmx dot de>]

Ken Brown <kbrown@cornell.edu> writes:

>> This is also a D-Bus client, which connects to the *same* session bus as
>> Emacs did due to $DBUS_SESSION_BUS_ADDRESS. Now you should see the
>> signal sent by dbus-monitor in Emacs.
>
> OK, I started the session bus the right way this time, but I still
> didn't see any signal from dbus-monitor in Emacs.  I assume I should
> have seen something in the echo area?

Yes. You could test whether both Emacs and dbus-monitor use the same bus
by reordering the calls:

- apply dbus-launch as described
- echo $DBUS_SESSION_BUS_ADDRESS
- in *another* shell, set $DBUS_SESSION_BUS_ADDRESS to this value, and
  start dbus-monitor
- start Emacs in the first shell, and load dbus.el. You shall see in
  the other shell output from  dbus-monitor, telling that an application
  has started. It will also tell you the name of that application, like
  ":1.2".
- apply (dbus-get-unique-name :session) in Emacs. The result shall be
  the same name.
- start dbus-monitor in the same shell as Emacs. In the other
  dbus-monitor, you should be notified, that an application has been started.

>> Maybe you can compile dbusbind.c with the compiler flag DBUS_DEBUG,
>> something like this in the Emacs source tree:
>>
>> # MYCPPFLAGS='-DDBUS_DEBUG' make
>>
>> This enables test traces sent to Emacs' stdout (the shell where you have
>> started it). I've introduced this flag while testing dbusbind.c, when it
>> has blocked Emacs, and I didn't want to start gdb ...
>>
>> Maybe I can see something suspicious in the traces.
>
> There's very little there.  It prints the two lines
>
>   xd_add_watch: fd 8
>   xd_add_watch: fd 9
>
> and no more.  Does this tell you anything?

It's the initialization phase. Two watch functions are installed on file
descriptors 8 and 9 (connected to the system and session buses), polling
for incoming messages in Emacs' mainloop.

When you call dbus-get-unique-name, there shall be more output. But this
works, as you have confirmed, so this is not the interesting case.

I've hoped to see more :-( Did you play with the running/non-running
system bus?

Anyway, I need to debug when I'm back.

> Ken

Best regards, Michael.

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