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

Subject: Re: put callback queuing
From: Andrew Johnson <anj@aps.anl.gov>
To: tech-talk@aps.anl.gov
Cc: Daron Chabot <daron.chabot@gmail.com>
Date: Thu, 21 Jun 2012 10:42:55 -0500
Hi Daron,

On 2012-06-21 Daron Chabot wrote:
> Recently at BNL, we've been investigating a report of unexpected
> behavior found when using put-callbacks to a Motor Record (verified
> using a simulated motor). After initiating a long-running motion with
> 
> caput -c -w 100 test:motor1 <some large value>
> 
> trying to stop the motor in the following way fails:
> 
> caput -c -w 100 test:motor1.STOP 1

...

> I can understand serializing put-callbacks on a per-channel basis, but
> the implementation appears to serialize _per-record_.
> 
> What am I missing? A little help please...

That's how the putNotify code works inside the IOC; there can only be one 
putNotify operation outstanding on any record at a time, basically because 
there is only one field in each record that stores the putNotify status 
information, it's too hard to try and keep track of multiple operations at 
once, and it's questionable what that would actually mean.  The putNotify 
functionality has to keep track of the putNotify state through asynchronous 
record processing and across PP database links, which makes it pretty 
complicated.  There is an enhanced version of the putNotify code called 
process-get which Marty wrote in 2008 that will be in the 3.15.0 release, but 
it doesn't change the 'one notify per record' limit that you've hit.

Thus you should *not* use put-callback for writing to the .STOP field, for 
exactly this reason, use a regular put:

caput test:motor1.STOP 1

HTH,

- Andrew
-- 
Never interrupt your enemy when he is making a mistake.
-- Napoleon Bonaparte

Replies:
RE: put callback queuing Hill, Jeff
References:
put callback queuing Daron Chabot

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