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

Subject: Re: Keck portable CA server usage
From: saa@SLAC.Stanford.EDU
To: wlupton@keck.hawaii.edu
Cc: tech-talk@aps.anl.gov
Date: Fri, 06 Nov 1998 10:25:36 -0800 (PST)
>The software seems to be reliable and efficient. We had some crashing
>problems (with large arrays) under Beta11 but we believe that these are
>fixed in Beta12 (the problem was in GDD, not in the CA server library).
>We do still have a problem with asynchronous i/o that completes after
>the CA client has exited; we would be interested to hear other peoples'
>experience of asynchronous i/o.

Hi William -

I attempted to use asynch I/O in my CA server for BPM (beam position
monitor) acquisition.  But most clients just don't have a long enough wait 
for gets to complete.  I also had some problems with the CA server crashing 
when a client exits before IO completion (I was using beta11 - not tried it
with beta12).  I didn't explore this problem further since I didn't want to 
change all our EPICS clients to use longer get timeouts.  Instead,
for now, people have to use monitors when they want BPM data and, if they
are the first one to post the monitors, they have to wait for data with good 
status to come if they want to use the data.  If they do a get, they'll
just get zero data with a "timeout" status.  The fundamental problem here is 
that our existing old non-EPICS control system does not cache BPM data 
anywhere - all acqs are done on-demand using about 30 different acq parameters
set up by the clients before the acq.

This situation is not ideal and obviously needs more thought and work as
time permits.

Stephanie

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