[avahi] Race condition using the avahi D-Bus interface?

[amo.vanbemten at student.ulg.ac.be]

Hi,

I'm applying a similar approach and I have no problems.
My code:

try:
  path_to_browser = self.server.ServiceBrowserNew(interface,
                                                  protocol,
                                                  stype,
                                                  domain,
                                                  dbus.UInt32(0))
  proxy = self.bus.get_object(bus_name = avahi.DBUS_NAME,
                              object_path = path_to_browser)
  ifc = dbus.Interface(proxy, avahi.DBUS_INTERFACE_SERVICE_BROWSER)
except DBusException as e:
  self.stop(error = "Error with the Avahi daemon. Is it still running? " +
                     "Error : %s." % e)
  return

ifc.connect_to_signal('ItemNew', self.newService)
ifc.connect_to_signal('ItemRemove', self.removeService)


does not suffer of race conditions problems. I've been testing
it on networks with hundreds of services and I apply such a 
scheme several times (creating a ServiceBrowser, creating a new
ServiceResolver, creating a new RecordBrowser and so on) without
ever having any problem.


----- Mail original -----
De: "Danny Smit" <danny.smit.0 at gmail.com>
À: avahi at lists.freedesktop.org
Envoyé: Mardi 23 Décembre 2014 16:22:29
Objet: [avahi] Race condition using the avahi D-Bus interface?

Hi everyone,

I'm running into a problem with avahi which looks similar to the
following reported issue: http://avahi.org/ticket/247

However in this case I'm using c++ / Qt to connect to the avahi
daemon. This basically exists out of two steps:

1. Create a ServiceBrowser using the D-Bus API ServiceBrowserNew
2. Connect to the ItemNew signal of the created ServiceBrowser

It seems that at step 1 the browser immediately start resolving
services and that it may occur that the ItemNew signal is emitted even
before step 2 is finished. The way the avahi ServiceBrowser is
designed, there is no way to influence this. From my point of view it
looks like this design is prone to race conditions.

My question is, how is this supposed to work? Should I use the avahi
interface differently? Or is this a bug in the design of the avahi
ServiceBrowser D-Bus interface?

Any help would be greatly appreciated.

Kind regards,

Danny
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