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<== Date ==> <== Thread ==>

Subject: Disconnected PVs
From: "Andrew C. Starritt" <Andrew.Starritt@synchrotron.org.au>
To: EPICS Tech Talk <tech-talk@aps.anl.gov>
Date: Wed, 11 May 2011 10:29:17 +1000
Hi all,

As part of the "ca.py - Throws error - workaround" thread there was some 
discussion whether a CA client should call ca_clear_subscription when it
detects that a server has disconnected and presumably re-subscribe when
the server re-connects.

Although the CA library automatically maintains the subscription, wouldn't 
it be better that when the PV re-connects, the client should do a ca_get 
(or ca_get_array or ca_get_array_callback) and a new ca_create_subscription.

I would do this because the nature of a PV might have changed and a new 
ca_get would ensure that the client has the latest associated data 
(e.g. precision, EGU, enumeration values), and a new subscription because 
the field type and/or number of elements may have changed as well.

Although such PV changes are relatively rare, they do occur. 

Any counter arguments?  

--
Andrew Starritt | Principal Controls Engineer | Australian Synchrotron
p: (03) 8540 4164 | f: (03) 8540 4200
andrew.starritt@synchrotron.org.au | www.synchrotron.org.au
800 Blackburn Road, Clayton, Victoria 3168


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Replies:
Re: Disconnected PVs Matt Newville
Re: Disconnected PVs Andrew Johnson

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