Re: pyepics not updating pv.enum_strs after connection

[Matt Newville <newville@cars.uchicago.edu>]

Hi Andrew,

On Wed, Mar 25, 2015 at 11:21 AM, Andrew Johnson <anj@aps.anl.gov> wrote:

On 03/25/2015 10:55 AM, Dirk Zimoch wrote:
> On 25.03.2015 04:46, Matt Newville wrote:
>> Yes, I think this idea of getting the ctrl variables in the connection
>> callback is a good idea, and will allow more straightforward code  As it
>> is, a pyepics.PV is already expected to be a "rich" object, even if
>> sacrificing ultimate performance, and is normally expected to have the
>> ctrl variables.   So, I think it's reasonable to have this getting of
>> ctrl variables as the default.    I'll add that.
>
> This is generally a good idea for every ca client. After a reboot,
> anything may have changed: Enum strings, limits, units, precision, array
> size, even record type (and thus data type).

Recent versions of Base (3.14.11 on) have a CA monitor event type
DBE_PROPERTY which was intended for monitoring changes to metadata like
the ctrl variables. 3.14 IOCs don't send out many property events (and
the PV Gateway doesn't support property subscriptions yet either), but
as 3.15 and later IOCs come in they make the case for using this quite a
bit more compelling. I would encourage CA client developers to read the
tech-talk threads discussing DBE_PROPERTY first though, there are a few
gotchas.

Is it reasonable to simply change the event subscription mask to include DBE_PROPERTY by default?  Will doing so work (in the sense of "not fail"), even though only getting VALUE, LOG, and ALARM events) for older iocs and through gateways?  If so, that's an easy change to make.

Cheers,

--Matt Newville
 

- Andrew
--
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