Experimental Physics and
Industrial Control System

[email protected] (William Lupton) · Tue, 3 Nov 1998 13:36:22 -1000

re...

>> It sure would be nice to have an option in the sequencer that would
>> use ca_put_callback() ... i.e. a call that wouldn't return until
>> record processing caused by the 'put' was complete. I'm trying to work 
>> with a device that is quite unpredictable in its response time.
>
>It would also be nice to get a 'done' event corresponding to a 'put'
>without hanging at the 'put' call.

I agree with both suggestions. ca_put_callback() really should be supported
and you really shouldn't have to block until the callback has been delivered.

Off the top of my head, how about the following spec:

pvPut( var );		/* existing behavior */

pvPut( var, wait );	/* use ca_put_callback(); if wait==TRUE, block on
			   completion with some pre-determined timeout */

pvPut( var, wait, timeout );
			/* as above but specify the timeout */

if wait==FALSE, pvPut() will not block and completion can be checked by using

when ( pvPutDone( var ) ) {
}

which will fail if no put is active, or wait for put completion otherwise.
Timeouts can be handled using the normal delay() mechanism. There would
probably also need to be a pvPutActive( var ) enquiry function.

I can't make any statement about when this might get done (assuming that
no-one gets there before I do). I would prefer to make this change only to
the still-unleased version that has the PV queueing facilities. We have been
using this operationally for several years.

Comments?

William

PS, Is there any interest in corresponding support for non-blocking gets?

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System