-----Original Message-----
From: [email protected] [mailto:tech-talk-
[email protected]] On Behalf Of Matt Newville
Sent: Thursday, April 14, 2011 10:07 AM
To: [email protected]; EPICS Tech Talk
Subject: Re: ca.py - Throws error - workaround
Hi Luca,
I hope it's OK with you that I'm sending the message to Tech-Talk,
where there are many people with much better understanding of Channel
Access than I have.
On Thu, Apr 14, 2011 at 1:58 AM, Luca Luisa<[email protected]> wrote:
Hi,
I'm working with PyEpics version 3.1.1.
My QT Python application communicates with many EPICS servers where
hundred
of PVs are delivered.
Our application has to deal with any EPICS server
disconnection/re-connection that can happen during the application run.
Each PV used by this QT Python application has a callback function
added
with the module "add_callback()".
When I noticed an EPICS server disconnection, I clear the callbacks
with the
method "clear_callbacks()".
When any EPICS server re-connect again, I try to add again another
callback
function to the same PV instance previously created, if fails (the
add_callback returns None) I re-create the PV instance again and try to
add
the callback function.
But in the cycle above described used to handle the dynamic connection
to
EPICS server, I get a lot of unknown errors in the terminal from where
I
launch my application, those are:
-----------------------------------------------------------------------
--------
TypeError: __on_connect() got an unexpected keyword argument 'count'
Traceback (most recent call last):
File "_ctypes/callbacks.c", line 295, in 'calling callback function'
File "/usr/local/lib/python2.6/dist-packages/epics/ca.py", line 420,
in
_onGetEvent
args.usr(value=value, **kwds)
-----------------------------------------------------------------------
--------
Our application is very complex so I cannot send you an example.
In order to remove this error that full-fills the terminal window, I
had to
change the "ca.py" source with a try: except: statement.
The diff is:
419,423c419,420
< try:
< if hasattr(args.usr, '__call__'):
< args.usr(value=value, **kwds)
< except:
< """"""
---
if hasattr(args.usr, '__call__'):
args.usr(value=value, **kwds)
My solution is a pure workaround to make my application working and I
got
success but I would like to know if this is a known error or my way to
handle connection/disconnection of a EPICS server is wrong.
Many thanks
Ing. Luca Luisa
I'm reluctant to make that change, as it's the only place ca.py can
tell the programmer that there was an error in running the
user-supplied callback and this change silences that message.
This message:
TypeError: __on_connect() got an unexpected keyword argument 'count'
Traceback (most recent call last):
File "_ctypes/callbacks.c", line 295, in 'calling callback function'
File "/usr/local/lib/python2.6/dist-packages/epics/ca.py", line 420,
in
_onGetEvent
args.usr(value=value, **kwds)
says that PV.__on_connect() -- the internally defined connection
callback for a PV -- is being run as a change-in-value callback. I'm
not sure how that's even possible.
When I noticed an EPICS server disconnection, I clear the callbacks
with the
method "clear_callbacks()".
I'm not sure this is necessary. Have you tried not doing this?
Obviously, you won't get a callback from a disconnected PV, and will
get a callback upon reconnection, but I would think that's not worse
than explicitly clearing and re-setting callbacks. I can verify that
it does works for me in simple test scripts to not clear "change
value" callbacks and restart the server IOC.
When any EPICS server re-connect again, I try to add again another
callback
function to the same PV instance previously created, if fails (the
add_callback returns None) I re-create the PV instance again and try to
add
the callback function.
For PV.add_callback() to return None, the PV has to be unconnected --
or at least that's the intention. So it's hard to understand what's
happening if you wait for reconnection to add a callback. I do think
it shouldn't be necessary to re-create the PV.
I'm not sure whether this is related to using QT. A minimal example
would be really helpful.
--Matt
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