Experimental Physics and
Industrial Control System

Jameson Graef Rollins <[email protected]> · Thu, 14 Aug 2014 22:52:33 -0700

On Thu, Aug 14 2014, Matt Newville <[email protected]> wrote:
> Sorry for the trouble.  The basic issue here is that PV.get() relies (by
> default) on a callback on the monitored value to keep the PV's value
> up-to-date, avoiding explicit calls to ca.get().    The put(wait=True) or
> put-with-callback uses a *different* callback on the put() request.    When
> the put-callback completes, the callback for the monitored value may not
> have been run.

Hey, Matt (and Mark).  Thank you both so much for the speedy responses.
I suspected I was seeing the race condition that you both describe.

> It's reasonable to say that when the put-with-wait completes that the
> cached value  should be updated.  I'll look into that.

Yeah, if that was possible I think that might best jive with
expectations.  Thanks for looking into it.

> The alternative is to:
>     for i in range(10):
>         pv.put(i, wait=True)
>         print pv.get(auto_monitor=False)
>
> which will make an explicit call to ca.get() every time, not relying on the
> monitored value.   That will add a potential delay, but is probably the
> safest way to ensure that the value is the current one.

I think this is probably the solution I'm looking for, although I need
to ponder whether or not the overhead of a full get() is worth it.
Seems like just reporting the newly written value is sufficient for our
purposes.

Thanks again for the help.

jamie.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System