Experimental Physics and
Industrial Control System

Ben Franksen <[email protected]> · Thu, 28 Oct 2010 00:29:26 +0200

On Mittwoch, 27. Oktober 2010, Tim Mooney wrote:
> One point that is probably obvious to you guys, but was obvious to me
> only in retrospect,
> is that it matters *where* in the processing chain the asynchronous
> record occurs.

It was not obvious to me, thanks for pointing it out.

> If the only asynchronous record in the chain is the first one, you
> can get good behavior
> from a sequence of ca_put_callbacks and be fooled into thinking that
> server-side code
> is more aware of putNotify than it actually is.  This is because the
> first record's PACT field
> will be True all the while the putNotify is active, so server-side
> code, which only honors
> record locks and PACT fields, will accidentally be honoring putNotify
> as well.
>
> To make a good ca_put_callback test, you have to write to a
> synchronous record that links
> to an asynchronous record.  In this case, when the first record has
> written to the asynchronous
> record, and that record has gone into its asynchronous wait, both the
> lockset and the
> first record's PACT field will look ready for another
> ca_put_callback, but the putNotify
> fields will not be ready, and you'll be able to see the problem you
> need to defend against.

Jeff, can you confirm this, i.e. does the server only look at PACT, and 
not at the putNotify fields? If yes, do we treat this as a CA bug (to 
be fixed in the next base release)?

(I may offer a work-around in any case, but I'd still like to know what 
the specified behaviour is, so that work-arounds can be marked as such 
and phased out when implementation and spec cease to differ.)

Cheers
Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System