Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Tue, 05 Feb 2008 11:11:30 +0100

Hello Dehong,
unfortunately EPICS does not support this.
What I normally do is to write a 1 to <record>.PROC via ca_sg_put. This call
completes when the the record has finished processing. (You can also use
ca_put_callback instead.) Then, I read the value with a ca_get. Of course, this
is not an atomic action as there are two channel access calls involved. That
means, it is possible that a second client processes the record again before you
could read and you will read his value instead of yours. But this is normally
not a problem.
It is a pity that EPICS leaks atomic process-and-read and read-modify-write calls.
Dirk

Dehong Zhang wrote:

Hi,
Is it possible to set up a passive record/field, which will only be processed
when some channel access client tries to read it?
Thanks and best regards,
Dehong

--
Dr. Dirk Zimoch
Paul Scherrer Institut, WBGB/006
5232 Villigen PSI, Switzerland
Phone +41 56 310 5182

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System