Re: ca_put_callback once again

[Ralph Lange <Ralph.Lange@bessy.de>]

 On 24.11.2010 12:36, Andrew Johnson wrote:
> One major problem is that generic code can't know whether it is safe to re-run
> a put that fails for this reason or not.  If there is significant I/O or other
> processing in the chain of records that leads up to the record that's busy
> then it might *not* be safe to repeat the put operation.  It doesn't matter
> where we propose to put the retry code, the same issue arises; only the person
> designing the overall system can work out what the correct response is.
>
> Ben's proposal at least makes it possible for the issue to be detected by a
> client so that an application-specific decision can be made when this happens.

+1

Returning a warning seems like the right compromise between the current 
behavior of returning OK (not even letting the client know that the 
situation occurred) and queueing/rerunning the process chain (which 
might be unsafe and/or unintended).
Providing the client with as much information as possible, without 
making assumptions of its intentions.

> This is definitely a 3.15 (or later) change by the way, and there is already a
> major modification to the putNotify code in the queue in front of this so I'm
> not going to be able to apply Ben's changes for some time, giving us a chance
> to work out the consequences properly.

For the sake of people using the sequencer under 3.14, we could make it 
a "known problem" and provide a patch on the EPICS web site.

~Ralph