Experimental Physics and
Industrial Control System

In a channel connection to any client, a good client either implements a cache or a queue. The cache allows the client to decouple the update rate of the monitor from the update rate of the client - such as a GUI that only updates at 10 Hz - where the monitor returns at 60 Hz. The queue allows the client to collect a finite set of monitors and then act on many of them at once - such as a data archiver. There is no case that I can think of where it is a good idea for a client to not do either of these.

Or are you talking about the "get" and "put" operations?



-----Original Message-----
From: [email protected] on behalf of Kasemir, Kay
Sent: Thu 10/20/2011 3:22 PM
To: Carcassi, Gabriele; [email protected]; [email protected]
Subject: RE: PVManager ReadOnly Check

Hi:

> Something like PV.isWriteAllowed() from org . csstudio . utility . pv would be
> nice.
I would go even further:
Something like o.c.utility.pv would be nice, period.

The PV manager is great for applications that need to read the average over the last 10 seconds
from N channels, updating at 1 Hz on thread X, expecting a list of Double, while filtering on
only data where ... is ... .
That's really great.
But of course you can't "write" to those PVs because how would you change the average
over the last 10 seconds? Go back 8 seconds and adjust that original value?

The good news is that the PVManager internally uses a 'DataSource' API that is similar
to utility.pv: It's the raw channel; pluggable implementations for EPICS V3, simulated channels,
then EPICS V4, or whatever you want to add in the future.

If we allow access to both
a) the DataSource API for those who need/want/prefer a raw channel API to read and write
b) a PVManager API that can average, queue, schedule update rates, handle thread access
.. I think we'd have it all.

Thanks,
Kay

References:

PVManager ReadOnly Check marcus . michalsky

RE: PVManager ReadOnly Check Carcassi, Gabriele

RE: PVManager ReadOnly Check Kasemir, Kay

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