Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Mon, 24 Jan 2011 09:13:48 -0700

The simplest approach might be to have a single thread with a main loop like
this. Threaded approaches certainly add complexity which might not be needed
in this situation.

static const double delay = 10.0
while ( true ) {
	List :: iterator chanIter = chanList.begin ();
	while (chanIter != chanList.end () ) {
		if ( chanIter->wereInterestedAndHaventSubscibed () ) {
			ca_create_subscription (...,&chanIter->subscr)
		}
		else if ( chanIter->weLostInterestAndAreSubscibed () ){
			ca_clear_susbscription ( chanIter->subscr );
		}	
	}
	ca_pend_event(delay);
}

Jeff
______________________________________________________
Jeffrey O. Hill           Email        [email protected]
LANL MS H820              Voice        505 665 1831
Los Alamos NM 87545 USA   FAX          505 665 5107

Message content: TSPA

With sufficient thrust, pigs fly just fine. However, this is
not necessarily a good idea. It is hard to be sure where they
are going to land, and it could be dangerous sitting under them
as they fly overhead. -- RFC 1925

> -----Original Message-----
> From: Patrick Thomas [mailto:[email protected]]
> Sent: Friday, January 21, 2011 6:38 PM
> To: Jeff Hill
> Cc: [email protected]
> Subject: Re: dynamic monitoring
> 
> Do you mean calling ca_pend_event(0) in the main program, and
> subscribing/unsubscribing in a separate thread? Is there an advantage to
> this?
> 
> On 1/21/2011 5:34 PM, Jeff Hill wrote:
> > Hi Patrick,
> >
> > The mechanism to start/stop a subscription is accessed via calls to
> > ca_create_subscription/ca_clear_susbscription. If you have a single
> threaded
> > application then you will need to start and stop the subscriptions from
> > within the main loop. Therefore, yes, that could be accomplished by
> calling
> > ca_pend_event with a finite timeout, deciding what subscriptions might
> be
> > needed, and calling ca_create_subscription/ca_clear_susbscription to
> start
> > stop the appropriate subscriptions - all of these actions in a loop.
> There
> > are of course many other, more complex, ways to schedule this including
> > changing to a preemptive callback mode application with multiple
> threads
> > (emphasis on complex) but of course a simple, minimal approach is often
> > just-a-fit for the design requirements.
> >
> > Jeff
> > ______________________________________________________
> > Jeffrey O. Hill           Email        [email protected]
> > LANL MS H820              Voice        505 665 1831
> > Los Alamos NM 87545 USA   FAX          505 665 5107
> >
> > Message content: TSPA
> >
> > With sufficient thrust, pigs fly just fine. However, this is
> > not necessarily a good idea. It is hard to be sure where they
> > are going to land, and it could be dangerous sitting under them
> > as they fly overhead. -- RFC 1925
> >
> >
> >> -----Original Message-----
> >> From: [email protected] [mailto:tech-talk-
> >> [email protected]] On Behalf Of Patrick Thomas
> >> Sent: Friday, January 21, 2011 6:01 PM
> >> To: [email protected]
> >> Subject: dynamic monitoring
> >>
> >> Hi,
> >>
> >> I was wondering what the best way is to dynamically monitor channels
> in
> >> C. That is to start and stop monitoring channels at run time. I
> >> currently have a program that connects to and attaches monitors to a
> >> predefined list of channels and then goes into a ca_pend_event(0),
> which
> >> blocks forever. Should I change this to a loop and specify a certain
> >> time period, i.e. ca_pend_event(1) and add or remove channels in that
> >> loop?
> >>
> >> Thank you for your time,
> >> Patrick

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System