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Subject: Re: Knowing if a server application is running
From: Bo Jakobsen <lister@f77.dk>
To: Ralph Lange <ralph.lange@gmx.de>, EPICS Tech Talk <tech-talk@aps.anl.gov>
Date: Wed, 18 Jan 2017 14:01:21 +0100
Thanks for all the input, many nice solutions
as always many ways to achieve the wished result.

I ended op with the solution below which matches my level of EPICS'ing nicely.

Best
Bo

On 2017-01-17 19:49, Ralph Lange wrote:
There are several ways to do that.

One that I have been using (and that is similar to Mark Rivers' suggestion) is a dead-man-switch setup:

A calc/calcout record is set up as always counting down, with SCAN e.g. set to 1 second and a CALC of e.g. "VAL>0?VAL-1:0".
The LOW and LOLO fields can be used to set a yellow and red alarm.
The monitored-system (e.g. your Matlab service) resets the timer regularly by e.g writing a 10 into the calc record every couple of seconds.
Using a calcout record the OUT link can be used (with OOPT set as "Transition to Zero") to trigger something when the service is dead.

This only needs a single record (EPICS database golf hole-in-one!), doesn't have to handle counter overflow situations, allows for a yellow and red alarm, lets the client freely decide for how long it will snooze, and is quite robust with respect to slightly irregular write intervals of the monitored-system (e.g. if the service is under high load). 

Cheers,
~Ralph



References:
Knowing if a server application is running Bo Jakobsen
Re: Knowing if a server application is running Ralph Lange

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