Re: Get notified of alarms internally to IOC w/o requiring record fields

["Johnson, Andrew N. via Tech-talk" <tech-talk@aps.anl.gov>]

Hi David,

Could you send us a (much) higher-level description of what you’re trying to accomplish with this work?

The code you show below is making use of APIs that as a Core developer I consider to be largely internal to the IOC and not intended for applications to call. That means we might make changes to these routines in future EPICS releases that could cause your code to no longer compile. It’s very unusual to be doing the kind of things that you are looking to do here, and that's a red flag to me — you might not know if/how the EPICS community already has solutions to the problem that you’re trying to solve. If you would let us know what that high-level problem is we might be able to point you in a different direction that doesn’t need as much code to be written.

In general, most normal EPICS applications don’t need the kinds of code that you’ve been asking about recently. I’m not trying to dissuade you from looking at our internals or implementing something useful that EPICS can’t currently do, but "trying to get notified of alarm states changing on PV’s without link fields or user events” isn’t a common EPICS IOC-centric thing.

- Andrew

-- 

Complexity comes for free, Simplicity you have to work for.

On 11/25/25, 11:03 AM, "Tech-talk" <tech-talk-bounces@aps.anl.gov> wrote:

Needed:

 

    auto dse = db_start_events(pctx, 0, 0, 0, epicsThreadPriorityCAServerLow);

 

 

From: David Bracey <dbracey@fnal.gov>
Date: Tuesday, November 25, 2025 at 9:06 AM
To: tech-talk@aps.anl.gov <tech-talk@aps.anl.gov>
Subject: Get notified of alarms internally to IOC w/o requiring record fields

I am messing around with some ideas, and I am trying to get notified of alarm states changing on PV’s without link fields or user events – basically without putting any requirements on PV’s or DB records.

 

I tried some code that intends to set a callback for the DBE_ALARM event, but I don’t seem to get called.  The code looks like this:

 

void my_event_func(void *user_arg, struct dbChannel *chan,

    int eventsRemaining, struct db_field_log *pfl)

{

    errlogPrintf("my_event_func\n");

}

 

int main(int argc,char *argv[])

{

    if(argc>=2) {

        iocsh(argv[1]);

        epicsThreadSleep(.2);

    }

 

    auto pctx = db_init_events();

    errlogPrintf("pctx %p\n", pctx);

 

    auto pchn = dbChannelCreate("SOME_");

    errlogPrintf("pchn %p %s\n", pchn, pchn ? pchn->name : "");

 

    auto psub = db_add_event(pctx, pchn, my_event_func, 0, DBE_ALARM);

    errlogPrintf("psub %p\n", psub);

 

    db_event_enable(psub);

 

    iocsh(NULL);

    epicsExit(0);

    return(0);

}

 

Does this seem feasible at all?

 

• Dave Bracey, Fermilab AD