Experimental Physics and
Industrial Control System

Matt Newville <[email protected]> · Wed, 20 Apr 2011 09:24:05 -0500

Hi Luca,

Is it possible to send a short example of code and the full error
message you're seeing?  That would really help diagnose the problem.
It should not be necessary (or even useful) to re-create a PV on
reconnection.

--Matt

On Wed, Apr 20, 2011 at 2:21 AM, Luca Luisa <[email protected]> wrote:
> Hi,
> I tried to types of code:
>
> 1. in the first one I don't disconnect the PV when the Server disconnects
> and I just wait an automatic reconnection.
> 2. in the second I disconnect the PV, and re-create it again when the server
> connects again.
>
> In both cases I get the same error.
>
> Luca
>
>
>
> On 04/19/2011 12:19 AM, Jeff Hill wrote:
>>
>> Hi Matt, Luca,
>>
>> Sorry about the delay responding - I was away on business at the end of
>> last
>> week.
>>
>>>> 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)
>>>> -----------------------------------------------------------------------
>>>>
>>
>> Despite some similarities, I don’t believe that this particular message
>> originates from the ca client library.
>>
>> Note also that if you do not unsubscribe when the circuit becomes
>> unresponsive then the ca client library will auto-magically re-subscribe
>> on
>> your behalf should the channel need to be reconnected on a fresh TCP
>> circuit.
>>
>> Jeff
>> ______________________________________________________
>> Jeffrey O. Hill           Email        [email protected]
>> LANL MS H820              Voice        505 665 1831
>> Los Alamos NM 87545 USA   FAX          505 665 5107
>>
>> Message content: TSPA
>>
>> With sufficient thrust, pigs fly just fine. However, this is
>> not necessarily a good idea. It is hard to be sure where they
>> are going to land, and it could be dangerous sitting under them
>> as they fly overhead. -- RFC 1925
>>
>>> -----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
>>
>
>

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System