Command line flag for number of threads

[orenbenkiki]

To create a setup where:

• There are multiple worker processes on different servers.
• Using multiple threads in each worker process.

Then one currently needs to jump through some hoops to setup the JULIA_NUM_THREADS environment variable for each worker process. Thus one can't use a simple addprocs with something like SshClusterManater. A possible workaround is writing a shell script which sets the environment variable and launches julia and specify this as the Julia executable.

It would be much more convenient and natural if julia provided a command line option for specifying the number of threads. If such a command line option is explicitly specified, it should override the value of JULIA_NUM_THREADS, if any.

This setup is useful because the threads within each worker process automatically share "everything" without having to resort to constructs like SharedArray. Of course this also means one needs to be more careful.

[non-Jedi]

This is a duplicate of #26889. Also relevant to your usecase is #16134 for your usecase.