All things related to multicast

[Bruce Rodger <>]

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                      
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