Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <[email protected]> · Tue, 2 Apr 2019 21:38:36 -0700

On 4/2/19 8:23 PM, William Cork via Tech-talk wrote:
> Hi All,
> 
> I’m working on a softIOC that will make calls to a Monit daemon to restart and monitor services under Monit.
> 
> Right now, I have the following pv structure (a wip):
> 
> |test:Monit:localhost structure string host http://localhost:2812 int poll 120 structure[] services structure string name testService boolean monitored true int state 0 string type SERVICE epics:nt/NTEnum:1.0 action enum_t value int index 0 string[] choices ["none", "enable", "disable", "start", "stop", "restart"] |
> 
> Is it possible to change an element in the nested services list with pvput, or are the immutable?
> |pvput test:Monit:localhost services='...'| may be the wrong syntax?
> More precisely, can I change services[index of service I care about].action = one of the action enums.
> 
> Architecturally speaking, is it more ideal to have a bookkeeping PVArray that lists the provided services and individual PVs for each service?

Are you thinking to control this with a existing client application?
eg. an OPI client like cs-studio?  I find that questions like this
are best approached by think from the prospective of a client.

What will a client want to do?  What steps are involved?
Are there any issues of atomicity (eg. racing with other
clients).  What configuration will a client need?

Now for the part for which I have a clear answer.

> pvput test:Monit:localhost services='...'

For the present the 'field=' syntax is limited to scalars and arrays of scalars.

It is possible to send an array of structures w/ pvput provided you're
building against Base >=3.15 (which includes a JSON parser).  The syntax
is awkward though:

> $ pvput -h 2>&1|grep JSON
>  JSON support is present
> Field values may be given with JSON syntax.

An empty array:

> pvput test:Monit:localhost '{"services":[]}'

One element with all default values.

> pvput test:Monit:localhost '{"services":[{}]}'

One element with one field having a non-default value.

> pvput test:Monit:localhost '{"services":[{"state":42}]}'

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System