rzmq | R package for ZMQ - R Bindings for 'ZeroMQ | Development Tools library

Worked:

The good news is,
the R-console reported the work-units got dispatched to the 4 worker jobs (ID: 6856) ...

To see how the acounting of CPU-usage works ( as in unix.time() ), test this ( the online R-code execution were not able to load either the library(foreach) nor the library(doParallel) to show the differences live, online, yet the code ought be clear on how to do that on a properly configured localhost R system :

Welcome to the Zen of Zero!
_{In case one has never worked with ZeroMQ,
one may here enjoy to first look at "ZeroMQ Principles in less than Five Seconds" before diving into further details}

Q : It does not display anything until I connect a client.

Sure, it does not, your code imperatively asked to block until a PAIR/PAIR delivery channel got happen to become able to deliver a message. As the v4.2+ API defines, the .send()-method will block during all the duration of a "mute state".

_{When a ZMQ_PAIR socket enters the mute state due to having reached the high water mark for the connected peer, or if no peer is connected, then any zmq_send(3) operations on the socket shall block until the peer becomes available for sending; messages are not discarded.}

May try non-blocking mode of sending ( always a sign of a good engineering practice to avoid blocking, the more in distributed-computing ) and better include also .close() and .term() as a rule of thumb ( best with explicit .setsockopt( zmq.LINGER, 0 ) ) for avoiding hang-ups and as a good engineering practice to explicitly close resources and release them back to the system

First, as ThorTL67 noted in the comments, it is a good idea to update your Rails version incrementally, not in one big leap. That way, your dependency issues will be less complex.

Check what version of Bundler you are using by running bundle version. If that version is old, it might be that some dependencies are not correctly calculated, and it might help to update Bundler (gem update bundler).

Then to the steps you can take to update from 4.2 to 'some higher version'. The list of errors that you got shows the conflicts between gem dependencies. You can try and tackle these conflicts one by one.

Solved! I had to install the zeromq source from here http://zeromq.org/intro:get-the-software