@bennedich thank you for the link.
To answer your question, this code was just a super simple example I made up to understand the basics of multi-threading. The original problem I posted is available at: https://discourse.julialang.org/t/problems-using-pmap-and-doubt-about-the-number-of-workers-processes-to-use/20510
(See also my second comment on it, in which I provide further details).
About the link you posted, let me ask you the following. You clearly distinguish between either:
multi-threading (single computer, multiple cores), or parallel computing (cluster, several distributed machines)
In my case I am using one multi-core computer. Does that mean that I cannot use parallel computing at all (and thus pmap())?