All things related to multicast

[Frank Fulchiero <>]

Just to remind everyone, we have a new SAP announcer available, which  
has been working fine for a few months.
http://nutmeg.conncoll.edu/wiki/index.php/ESA

I am trying to see if we can post it, in the meantime, I can email it  
to anyone that would like to evaluate or use it.
Let me know if you would like the OSX, Windows, or Linux version.

Thanks,
Frank Fulchiero
Digital Media Specialist
Connecticut College


On Sep 3, 2008, at 7:24 AM, Bruce Rodger wrote:

> On Thu, 26 Jun 2008, 
>
>  wrote:
>
> > miniSAPserver in its current (buggy) form has been around
> > for ages....and yet thee storms have only just started to
> > occur.  is it, perhaps, that some 'config example' which
> > is out there i the one causing this issue
>
> I've just managed to unintentionally reproduce the problem.  
> Fortunately, it
> was noticed quickly, and hopefully was only local :)
>
> miniSAPserver version 0.3.4
> on Ubuntu 7.10
>
> The default config contains:
>
> # Number of seconds between announces. 5 is default. Internet  
> announces better use 30.
> sap_delay=5
>
> If you use this default, all is OK. If you add the "-s" flag to the
> command, it prints a "." every time it sends out a sap. And as
> expected, we get a "." appearing every 5 seconds.
>
> However, if we make the suggested change and increase the value of
> sap_delay to 30 (in fact to any value greater than 15!) we get our
> SAP storm - thousands of SAPs (and thousands of dots on the screen)
> appearing per second.
>
> The problem appears to be an integer overflow in sapserver.cpp
>
>        unsigned n = config.Programs.size() ?: 1;
>         div_t d = div ((1000000000 / n) * config.GetDelay(),  
> 1000000000);
>         struct timespec delay;
>         delay.tv_sec = d.quot;
>         delay.tv_nsec = d.rem;
> (snip)
>         while(!should_exit)
>         {
>             for( unsigned int i = 0; i< announces.size() ; i ++ )
>             {
> (snip - send the SAP here)
>                 nanosleep( &delay, NULL );
>             }
>         }
>
> So it appears that when config.GetDelay is >15,  
> 1000000000*config.GetDelay
> overflows, the arguments to nanosleep are negative.... it doesn't
> sleep.... we get a storm.
>
> A quick workaround is to remove the "div" line, and just have
>         delay.tv_sec = config.GetDelay();
>         delay.tv_nsec = 0;
>
> I will leave development of a "proper" solution to someone else.  
> But I will log it on the videolan forum...
>
> Bruce.
> --
> Bruce Rodger                      
> |
> Network Manager, IT Services      |http://www.strath.ac.uk/IT/ 
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