Experimental Physics and
Industrial Control System

Steve Lewis <[email protected]> · Tue, 3 Nov 1998 16:55:23 -0800 (PST)

> >> 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?

1) I agree you should combine this with your PV-queue capable version.

2) Above calling sequences are OK, however, I think I prefer
	pvPut( var )
	pvPutCallback( var, wait, timeout )
	pvPutDone( var )

  a) I prefer to stick with a fixed number of arguments for given calling name
  rather than C++-style "different args is different semantics".

  b) I think timeout should be specified--what would a "good" values
  be for timeout?

  c) presumably if you choose wait==FALSE and later call pvPutDone(), when
  the original timeout expires it also fails, but with E_TIMED_OUT
  instead of E_NOT_WAITING.  And if it has succeeded already it returns
  OK, just as it does for normal unblocking?

--Steve

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System