Experimental Physics and
Industrial Control System

"J. Lewis Muir" <[email protected]> · Wed, 13 Oct 2010 12:32:21 -0500

On 10/13/10 10:08 AM, Josh Stein wrote:
> I would like to point out one warning with these embedded scripts -
> there is a very real possibility of breaking some higher level tools
> which rely on 'crawling' the startup command files for information. This
> very issue has just cropped up here at APS when the st.cmd structure of
> a number of our production IOCs was cleaned up during a recent 3.14
> upgrade.
> 
> In essence, some of our crawlers were unable to parse relevant tags
> since they failed to show up in the st.cmd file itself as those tags
> were moved to one or more of the 'sub-scripts'.
> 
> For now, the crawlers at APS are being re-written to follow the
> indirection. This is yet another example of how fragile the system
> structure can grow over time; the hooks into various parts actually
> increase the risk of things breaking as time progresses.

I don't think there should be anything wrong w/ using features supported
in the EPICS IOC shell.  The problem is the crawlers.  The crawlers were
fragile; they made assumptions about the st.cmd file.  To solve a
problem relatively quickly, sometimes this is OK, but then in a case
like this, one has to go back and fix it.  It could still be the right
decision.  Maybe one just needs some test cases to ensure the crawler
works for the cases needed or some checking script to ensure the crawler
is still working.

A robust crawler would actually be able to parse the IOC shell input,
constructing an abstract syntax tree or converting the input into some
other useful form, dealing w/ variable substitutions, etc., so the task
of the crawler could be implemented correctly.  This is obviously much
more work.

Lewis

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System