Interval timers on Fedora

[John Wendel]

Douglas Phillipson wrote:
> This probably isn't a Fedora specific question so I apologize if this is 
> the wrong forum.
> 
> Anybody know if you can set more than one interval timer in a single 
> process?
> 
> (setitimer())
> 
> Would starting more than one interval timer in a single process confuse 
> the signal system when delivering the SIGALRM to the receiving process?
> 
> In other words, can I have a 10 second interval timer which when times 
> out delivers a sigalrm to one function, and in the same process have a 1 
> second interval timer set to give a sigalrm to another function?
> 
> I'm having trouble with a second interval timer, it doesn't seem to 
> work, or deliver the signal to the desired function.  I'm using a 
> separate instance of struct itimerval and struct sigaction when setting 
> up the timers.  I have several books on the subject of interval timers 
> but none say you shouldn't do this, just "Every process has its own set 
> of timers".  But they might be referring to REAL, VIRTUAL, and PROF 
> timers, a single set of these for each process.
> 
> Opinions requested...
> 
> Thanks
> 
> Doug P
> 

I'm not an expert on this stuff, but my understanding is that 
setitimer gives your process access to one of three predefined timers 
(REAL, VIRTUAL, and PROF) and only the REAL timer is actually useful.
So your second call to setitimer is mucking up the settings from the 
first call.

See "man timer_create" for the POSIX timer stuff that lets you have 
lots of timers.

I recommend the O'REILLY book POSIX 4 by Bill Gallmeister for a good 
explanation of this fairly complicated topic.

Regards,

John