Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Wed, 27 Feb 2013 12:55:27 +0100

On Tuesday, February 26, 2013 10:17:12 [email protected] wrote:
> Thank you for your reply. I have now disabled preemptive callback.

Ok.

> I am
> using ca_poll to process the CA client and FileDescriptorManager.process
> to run the portable channel access server. These are called together in a
> single loop. However, once the CA client has attached to a number of
> process variables, the CA background activity that runs due to the ca_poll
> seems to delay the call to FileDescriptorManager.process too much. This
> results in calls to caget for process variables in the portable channel
> access server timing out. Is there another way to do this?

Have you looked at
http://lansce.lanl.gov/epicsdata/ca/client/caX5Ftutor-1.html yet? It contains
a lot of CA client examples and explains what calls to use in which situation.
You might be interested in chapter 4 "Monitoring a PV" and there especially
the section named "An Example Program" under which you'll find (among else) a
desciption of fdmgr, how it works and how it is used.

> Also, is there
> a way to avoid having the CA client search for process variables on the
> portable channel access server, but still look for them on the localhost?

Set EPICS_CA_AUTO_ADDR_LIST to NO and EPICS_CA_ADDR_LIST so that the gateway
is excluded but localhost is included.

Cheers
Ben

PS: The above link to the CA tutorial is not linked to from the EPICS home
page (or at least not in any prominent place). Could this be changed? I found
these pages extremely useful when trying to get my head around the CA client
API.

> > On Monday, February 25, 2013 14:58:36 [email protected] wrote:
> >> I think it turns out that the problem was
> >> that I actually had preemptive callback enabled and I should not have.
> >
> > Yes. If you use preemptive callback (i.e. multithreaded CA client) don't
> > create a FileDescriptorManager. It is only needed for single-threaded
> > clients
> > and can be used to centralize the call to select in case the CA client is
> > used
> > together with other stuff that wants to call select (such as a GUI
> > library).
> >
> > Cheers
> > --
> > Ben Franksen
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Ben Franksen
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System