Experimental Physics and
Industrial Control System

"Peregrine M. McGehee" <[email protected]> · Tue, 02 Sep 2003 11:56:04 -0600

Tim,
I concur with your fundamental idea and suggest that the .RPRO
field should contain a _list_ of structures to support
multiple writes from clients during the period when PACT==1.
The naive implementation is a simple FIFO queue for write requests,
although in general this should be a priority queue.
I think EPICS should never write to any record while PACT==1. (I'd like

to say that scanLock should persist through the I/O-wait period of
asynchronous

processing, so that dbPutField could not modify any field in a lockset
while

asynchronous processing was going on in that lockset, but I don't know
enough

about the consequences of this.) Anyway, maybe .RPRO should be used not
only

to signal that a record should be reprocessed, but also to cache the
field name

and value that should be written. This would handle the problem of a

dbPutField to a record during asynchronous processing that was started by

a dbPutLink. It wouldn't necessarily handle the problem of a dbPutLink to

a record during asynchronous processing that was started by a
dbPutField, because the record that caused the dbPutLink might have gone
on to initiate

other processing sensitive to the field whose write has been postponed.
- Peregrine
--
Peregrine M. McGehee	[email protected]	(505) 667-3273
Sloan Digital Sky Survey / Spallation Neutron Source
MS H820, Los Alamos National Laboratory, Los Alamos, NM 87545

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System