Enable OMCSessionZMQ to connect to an already running omc

[bilderbuchi]

As a user, I would like to be able to connect to an already running omc --interactive process that is listening at a certain host/port.
That is, I want OMCSessionZMQ to not start a separate omc process here if I pass in an endpoint, URI, socket/port that defines where my omc is listening.

This would be useful to enable OMPython to use an omc instance that is running elsewhere, e.g. in a managed container (that I can't start myself, so the present docker support does not help here) or on a (powerful) remote server.

[sjoelund]

OMC itself can be started to listen and perhaps you could connect to it. But it will only allow 1 connection and quits after the connection dies. It might not be so convenient to connect to it, but could perhaps be added as an option.

[bilderbuchi]

Sounds good! These restrictions would be OK for our use case.

I imagine I would independently start omc --interactive --interactivePort 666 and then in Python do
session = OMCSessionZMQ(port=666) (could reuse the existing port argument),
session = OMCSessionZMQ(uri='localhost:666') or
session = OMCSessionZMQ(uri='\\SOMEMACHINE:666') etc.

If omc can be convinced to not die after a connection dies, that could be useful, but that need is not currently on my radar.
More than 1 concurrent connection I don't see as too useful, currently (I imagine that would need significant rework in omc, too).

[arun3688]

@bilderbuchi , I guess we could use the existing port argument to connect to an existing omc connection, I can add that feature

[bilderbuchi]

@arun3688 great! I think that an additional host argument (defaulting to localhost) will be useful to pair with port, then one can easily assemble a proper connection string.

[scottlittle]

I would also like this feature. I am using a Mac host with a custom docker container with OpenModelica programs installed. I am able to connect to the container with a ZMQ session, but I am not able to use OMPython because of this.