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

Subject: Re: passive record/field to process when there is a CA read
From: Andrew Johnson <[email protected]>
To: Dehong Zhang <[email protected]>
Cc: [email protected]
Date: Mon, 04 Feb 2008 16:23:18 -0600
Dehong Zhang wrote:

Is it possible to set up a passive record/field, which will only be processed when some channel access client tries to read it?

Not using standard record types, and I wouldn't really recommend that you try to create a custom record type to do that because the database layer wasn't designed with that ability in mind â if you did manage to implement something like that, it could very easily break when a new release of Base comes along.


The IOC was designed so that in most circumstances requesting or even monitoring data from any field is a "safe" activity that should not significantly affect the continued operation of the control system. If someone could cause the control system's behavior to change just by getting a value through channel access, engineers would be *much* more careful when diagnosing an IOC with which they have little familiarity.

If you tell us what you're trying to achieve at a higher level, you might get some alternative suggestions on how to achieve that without needing to implement "process on get" semantics.

- Andrew
--
When a distinguished but elderly scientist states that something is
possible, he is almost certainly right.  When he states that something
is impossible, he is very probably wrong.  -- Arthur C. Clarke

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Re: passive record/field to process when there is a CA read Dehong Zhang
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