Re: Preemptive callback required

[Chris Mayer <cjm@observatorysciences.co.uk>]

Jeff,

 thanks for the explanation. Late yesterday I had followed the old 
advice "If all else fails read the instructions" and discovered your 
updated 3.14 CA manual. I just changed the task_initialize call  for 
context_create with preemptive callbacks enabled and sure enough it 
worked exactly as before. I haven't been through and replaced the other 
deprecated calls yet.

    Chris

Jeff Hill wrote:

> > dbServiceIO: preemptive callback required for 
> > direct memory interfacing
>
> A minor clarification:
> The message says "direct in memory interfacing" and not "direct memory
> interfacing". There should probably have been a hyphen in "in-memory". I fixed
> that for R3.15.
>
>
> > I looked at where the message was coming from but am not really 
> > any the wiser as to what it is trying to tell me. 
>
> In R3.13 the vxWorks version of the ca client library was implemented with
> preemptive calls to user registered callback methods, but this was not allowed
> or implemented on any other OS.
>
> In R3.14 preemptive callback is implemented on all OS, but this is optional, and
> the default is non-preemptive callback for backwards compatibility to the widest
> range of applications that do not run on vxWorks.
>
> Within the iocCore execution environment there is an efficient direct in-memory
> path between client requests and the database calls that implement them, and all
> socket related overhead is eliminated. In R3.14 this feature is currently
> requiring the preemptive callback execution environment, and it is not possible
> to create a channel unless you have preemptive callback mode enabled. I must
> admit that I don't clearly remember why I coded in this restriction so if its
> important, I could look into this further and see if it is still required. 
>
> However, given that Williams's application was probably running before under
> vxWorks in the R3.13 vxWorks ca client callback environment, then I assume that
> the simple solution will be to just enable preemptive callbacks when starting up
> a ca client context in the pvload utility. This is assuming of course that the
> pvload code was prepared to receive preemptive callbacks when it ran in the
> vxWorks preemptive callback environment provided under R3.13.
>
> Jeff
>
>
>
> > -----Original Message-----
> > From: Chris Mayer [mailto:cjm@observatorysciences.co.uk]
> > Sent: Monday, June 09, 2003 1:49 PM
> > To: tech-talk@aps.anl.gov
> > Subject: Preemptive callback required
> >
> >
> > I have just built William Lupton's pvload utility under 3.14.2 so that
> > I
> > can call it from iocsh on a Linux box. I ran it with a test file and the
> > records got set correctly at startup however, I got the following
> > message
> >
> > dbServiceIO: preemptive callback required for direct memory interfacing
> > of CA channels to the DB.
> >
> > I looked at where the message was coming from but am not really any the
> > wiser as to what it is trying to tell me. Before I start looking at the
> > pvload code can someone explain what circumstances would trigger this
> > message.
> >
> >  Regards
> >
> >   Chris Mayer
> > _______________________________________________________________________
> > Observatory Sciences Ltd.          Email: cjm@observatorysciences.co.uk
> > William James House                Tel: 44 - (0)1223 - 508257
> > Cowley Road,                       Fax: 44 - (0)1223 - 508258
> > Cambridge, CB4 0WX, UK             http://www.observatorysciences.co.uk


--
_______________________________________________________________________
Observatory Sciences Ltd.          Email: cjm@observatorysciences.co.uk
William James House                Tel: 44 - (0)1223 - 508257
Cowley Road,                       Fax: 44 - (0)1223 - 508258
Cambridge, CB4 0WX, UK             http://www.observatorysciences.co.uk