Experimental Physics and
Industrial Control System

"Wang Xiaoqiang" <[email protected]> · Thu, 5 Mar 2009 10:27:55 +0100

Hi pythoners,

If you ever used Geoff Savage's caPython/CaChannel extension in a
multithreaded program, you may know its limitation already: you can only
issue CA calls in the main thread. It is still using EPICS 3.13 API and
is not aware of the ca context attach/detach calls introduced in EPICS
3.14. 

At that time (July 2008), I am not aware the update done by John
Hammonds of APS. I only know Noboru Yamamoto of KEK has maintained a
thread-aware PythonCA extension over years, which provides a low level C
extension to CA library as well as a convenient high level class
"channel". 

For the sake of maintaining legacy codes, I write a new CaChannel class
with the same API as the old, using PythonCA C extension. Now it has be
used in SLS for months and the result is satisfactory. Without a single
line modified, programs using CaChannel, epicsPV, ca_utils run smoothly.
It provides "transparent" multithread support and no extra efforts have
to be taken for threaded CA calls.

Here is a short instruction on how to get the code,
http://controls.web.psi.ch/cgi-bin/twiki/view/Main/NewPythonEpicsInterfa
ce#Install

If this CaChannel does not work for you, please kindly let me know the
reason. I would like to thank Noboru Yamamoto to merge my changes and
please contact him if it blows up your computer :D. 

--
Dr. Xiaoqiang Wang
Paul Scherrer Institut, WBGB/010
5232 Villigen PSI, Switzerland

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System