<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><br></div><div><div>On 05/11/2009, at 6:16 PM, José Félix Ontañón wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><br><br><div class="gmail_quote">2009/11/5 Trent Lloyd <span dir="ltr"><<a href="mailto:lathiat@bur.st">lathiat@bur.st</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Hi Jose,<br> <div><div></div><div class="h5"><br> On 05/11/2009, at 6:35 AM, José Félix Ontañón wrote:<br> <br> > Hi everyone!<br> ><br> > I'm a newbie playing with python-avahi trying to code some kind of<br> > master-slave application for shutdown every machine at same time.<br> > When the master it's ordered to shutdown, it sends the signal to the<br> > slaves. The slaves publish/unpublish the service via avahi, and the<br> > master<br> > discover them via ItemNew/ItemRemove signals. Very strait-forward,<br> > isn't?<br> ><br> > The avahi publish/unpublish/discover services it's gorgeous but i've<br> > found that if a slave, that has published the service via avahi,<br> > losts it<br> > network (i.e. the wifi ap goes out of power), the master still<br> > discovering it! and no ItemRemove signal it's raised at all. Is it<br> > normal? Am i doing something wrong?<br> ><br> > To solve it, i've implemented some kind of "ping" to the slaves<br> > service every Xseconds. When a new slave it's discovered, the<br> > periodic ping starts.<br> > When ping it's failing i know there be some problem with networking.<br> ><br> > I wonder if avahi itself provides a native workaround to avoid the<br> > coding of those nasty "ping" cycles ...<br> <br> </div></div>This is normal.. it will disappear after some time.<br> <br> The instant removal of an advertised service relies on the host<br> sending a "gone away" message (more specifically, it updates the TTL<br> of its record to expire in I think.. 1 second)<br> <br> This is because mDNS uses caching.. if it didn't use caching it would<br> cause alot more network traffic and would hammer especially wireless<br> networks.<br> <br> <br> <br> Having not really worked with it for a while.. I can't remember all<br> the details but I suspect you can change the TTL in the Avahi API call<br> to make these timeouts happen a little quicker, but you will increase<br> network traffic by doing so.<br> <br> Really your application should not rely on Avahi for "service<br> undiscovery".. it's meant generally for "unreliable service<br> discovery".  You are best of actually having some protocol between the<br> master and slave and just using avahi for the slave to find the master<br> in the first instance.<br> <br> Regards,<br> Trent<br> _______________________________________________<br> avahi mailing list<br> <a href="mailto:avahi@lists.freedesktop.org">avahi@lists.freedesktop.org</a><br> <a href="http://lists.freedesktop.org/mailman/listinfo/avahi" target="_blank">http://lists.freedesktop.org/mailman/listinfo/avahi</a><br> </blockquote></div><br><br>Ok, in this case i'll continue with my ping aproximation. It works fairly well.<br><br>Thanks Trent.<br clear="all"><br></blockquote></div><div>From what I remember reading the docs, what is supposed to happen is when someone goes to try and use a service that is no longer there, it should fail and immediately flush that entry from the cache so that its no longer an option in the user interface.</div><div><br></div><div>Rob</div></body></html>