Experimental Physics and
Industrial Control System

Steve Lewis <[email protected]> · Mon, 17 Oct 2005 12:59:20 -0700

At 1:23 PM -0600 2005/10/17, Jeff Hill wrote:

Proper uniform definition of connection responsiveness notification
interfaces is also a very important issue that is often overlooked in a
first cut CORBA based approach. In any case that was what the reviewers
commented about initial efforts at NIF.

I was one of those early reviewers. Although we did not see the full

negative implications and coupling of the wide, early-binding

interfaces, we did notice the fundamentally synchronous nature of the

CORBA in use (again, the available vendors did not support the event

system and some other CORBA features).

Much was done (by the vendors and the NIF developers) to mitigate

this, but when either a tier-1 or tier-2 program dies, often it is

not possible to smoothly re-insert it into the mesh of still running

programs in all 3 tiers. There are also messages queued up deep in

the (opaque) CORBA and TCP/IP layers that "assault" a newly restarted

IOC and can cause it to fail again. Often the only recourse is to

tear down a substantial block of tier-1, -2, and -3 programs and

restart them in a benign order.

A non-solution is the practice of storing the dynamic connection

information (CORBA references) back in the RDB: after a really nasty

crash, the RDB has to be (manually) scrubbed, since no starting order

works. This might have implications for a central nameserver in a

3-tier EPICS system--unless you think there will be no "nasty

crashes" ever :-)

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System