Experimental Physics and
Industrial Control System

"Carcassi, Gabriele" <[email protected]> · Thu, 20 Oct 2011 12:33:32 -0400

Hi again:

While we are at it, let me list the other deficiencies of the write part
(if you were at the EPICS meeting, there is a reason all the examples in
the pvManger talks were reads ;-) ).

1. ReadOnly default. Right now you have to assume the channel is
writable until you are told it's not. It should be the other way around
(you assume it's not writable until you are told it is). Again, not
clear how to do this in the complex case (do I need everything to be
connected to be able to write? It depends... how do I say it, possibly
in a compact way?) 
2. Write queue. pvManager should handle the following cases:
   - write directly without waiting for previous write to end (no queue)
   - wait for last write to complete (queued), in which case you need to
specify the queue length. If the queue is full (say with C, B, A) drop
the oldest one (and become D, C, B).
Right now everything is the first case, _even for the sync case_ (if you
write from different threads). The async case should default to the
first case, while the sync case should default to the second with a
queue of one. 
3. If you write a complex object, and of the channel write fails, you
currently do not have a good way to:
   - specify whether the write should continue to all channels or not
   - understand which specific writes failed (problem is potential
in-flight operation that may fail and the requirement of one callback
per write)
And there may be others that I do not realize yet, of course... ;-)

What is there allows to do basic things. It still need to be developed
to be at the same level of the read. 

Gabriele

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
[email protected]
Sent: Thursday, October 20, 2011 7:49 AM
To: [email protected]
Subject: PVManager ReadOnly Check

Hi,

I have a setup of CSS, PVManager and a custom plugin. In the custom
plugin is a jface table viewer containing information based on process
variables.
Depending on whether that PV is writable I would like to offer
EditingSupport in certain cells.

Is there another way to check if a PV is writable/readonly in advance
instead of registering a PVWriterListener and catching a
WriteFailedException after trying to write to a readonly variable ?

Something like PV.isWriteAllowed() from org.csstudio.utility.pv would be
nice.

Thanks,
Marcus

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System