Experimental Physics and
Industrial Control System

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.