Calc record with two CP input links ending up in inconsistent state

[Érico Nogueira Rolim via Tech-talk <tech-talk at aps.anl.gov>]

Hi!


I updated an IOC today with ~100 instances, and came across a bug in
only one of them. The new version of the IOC has a calc record with two
input links to PVs in the same IOC, using "CP" links. For the one IOC
with the bug, the calc record's VAL was inconsistent with the value of
the two input PVs: CALC is "A & B", the two PVs were 1, but VAL was 0.
Internally, the calc record was consistent, because A was indeed 1, but
B was 0. I tried using dbpf to force the calc record to process itself,
but that didn't update the value of B; the only way to force the calc PV
to change was to force the PV linked to INPB to change its value.


The two input PVs are I/O Intr PVs using asyn record support, which are
usually updated (to 1) during IOC startup, and then stay there.


It seems possible that there could be some sort of race during startup,
after iocInit completes and the calc record processes its first monitor
events, but I'm not sure how best to debug this (nor how to reproduce
it; I only managed to catch it in the production environment due to
amount of devices).


I originally considered that using multiple CP input links would
guarantee eventual consistency; was I wrong in this assumption, or is it
likely that there is a bug in the record/link implementation?


Cheers,

Érico


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