Re: monitors received out of order

[Tim Mooney <mooney@aps.anl.gov>]

On 11/2/2010 10:17 AM, Ernest L. Williams Jr. wrote:
> Tim Mooney wrote:
> > Dear folks,
> >
> > I have two records, and a separate task monitoring a field that both records
> > post, all in the same IOC.  Most of the time, my task receives monitors in the
> > order in which they were posted.  But sometimes, the task receives a monitor
> > from record B before it receives a previously posted monitor from record A.
> > (I know for sure which record is posting first, because record A posts before
> > causing record B to process.  Also, I've modified the record to set its time
> > stamp immediately before posting, and I get another time stamp on entry to
> > the monitor routine.  The time ordering of those stamps does not agree.)
> > I've seen this on solaris and Linux, but not on vxWorks.
> Hi Tim,
>
> When you run an IOC on Linux the EPICS Priorities are not map properly unless 
> you run the IOC as root.
> All tasks are given the same OS priority.
> Are you running the Linux IOC as root?
No.  Although the original problem was reported for a Linux system, most of my
testing has been on solaris.  Do you know if this also applies to solaris?
> > I have code that misbehaves when this happens, so I started digging around
> > and have convinced myself that I should not be relying on the time ordering of
> > monitors received from different records (even when those records are running
> > in the same task).  I now think I can rely on posts from a single record 
> > arriving in
> > time order, but not posts from different records.  I think this because 
> > events from
> > different record go into different queues, and there doesn't seem to be any code
> > in the vicinity that seems worried about time ordering across event queues.
> >
> > Am I right about this?

--
Tim Mooney (mooney@aps.anl.gov) (630)252-5417
Software Services Group, Advanced Photon Source, Argonne National Lab.