Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Thu, 15 Aug 2013 17:18:12 +0200

Hello all,

Is it possible to make a database link wait for completion?
If not, is this worth to be considered for a future EPICS version?

Example:

A seq record S triggers two records, A and B. A has an asynchronous

device support (or is the beginning of a processing chain that contains

an asynchronous device support).

record (seq, "S")
{
   field (LNK1, "A.PROC PP")
   field (LNK2, "B.PROC PP")
}

record (ai, "A")
{
   field (DTYP, "async dev sup")
   field (INP,  "...")
}

record (ao, "B")
{
   field (OMSL, "closed_loop")
   field (DOL,  "A")
   field (OUT,  "...")
}

When I do a caput with callback to S, the call only returns after A and

B have both processed, as expected.

caput -w 10 -c S 1

However, B starts processing before A has finished. That is because A is

asynchronous. Thus A has only just started processing when B is

triggered. This is bad if B (or something down its processing chain)

depends on A because B gets an old value.

Now it would be nice to have "put notify" links, e.g:

   field (LNK1, "A.PROC PN")

So that LNK2 is only processed when the whole LNK1 chain has finished

processing.

The same syntax and mechanism may be useful for input links too in order

to avoid getting old values from asynchronous device supports.

Any comments?

Does something like this already exists or is it already planned?

I think with dbPutNotify the necessary infrastructure is already there.

Dirk

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System