<div class="gmail_quote">2009/11/5 Trent Lloyd <<a href="mailto:lathiat@bur.st">lathiat@bur.st</a>> <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Hi Jose, <div><div></div><div class="h5"> On 05/11/2009, at 6:35 AM, José Félix Ontañón wrote: > Hi everyone! > > I'm a newbie playing with python-avahi trying to code some kind of > master-slave application for shutdown every machine at same time. > When the master it's ordered to shutdown, it sends the signal to the > slaves. The slaves publish/unpublish the service via avahi, and the > master > discover them via ItemNew/ItemRemove signals. Very strait-forward, > isn't? > > The avahi publish/unpublish/discover services it's gorgeous but i've > found that if a slave, that has published the service via avahi, > losts it > network (i.e. the wifi ap goes out of power), the master still > discovering it! and no ItemRemove signal it's raised at all. Is it > normal? Am i doing something wrong? > > To solve it, i've implemented some kind of "ping" to the slaves > service every Xseconds. When a new slave it's discovered, the > periodic ping starts. > When ping it's failing i know there be some problem with networking. > > I wonder if avahi itself provides a native workaround to avoid the > coding of those nasty "ping" cycles ... </div></div>This is normal.. it will disappear after some time. The instant removal of an advertised service relies on the host sending a "gone away" message (more specifically, it updates the TTL of its record to expire in I think.. 1 second) This is because mDNS uses caching.. if it didn't use caching it would cause alot more network traffic and would hammer especially wireless networks. Having not really worked with it for a while.. I can't remember all the details but I suspect you can change the TTL in the Avahi API call to make these timeouts happen a little quicker, but you will increase network traffic by doing so. Really your application should not rely on Avahi for "service undiscovery".. it's meant generally for "unreliable service discovery". You are best of actually having some protocol between the master and slave and just using avahi for the slave to find the master in the first instance. Regards, Trent _______________________________________________ avahi mailing list <a href="mailto:avahi@lists.freedesktop.org">avahi@lists.freedesktop.org</a> <a href="http://lists.freedesktop.org/mailman/listinfo/avahi" target="_blank">http://lists.freedesktop.org/mailman/listinfo/avahi</a> </blockquote></div> Ok, in this case i'll continue with my ping aproximation. It works fairly well. Thanks Trent. -- <a href="http://nosigasleyendo.blogspot.com">http://nosigasleyendo.blogspot.com</a>