Pass number of threads when starting Julia as an input argument

[enweg]

I am trying to set the number of threads to be used by JuliaCall via the code below:

Sys.setenv(JULIA_NUM_THREADS = 2)
# Sys.setenv(JULIA_HOME = "/Applications/Julia-1.8.app/Contents/Resources/julia/bin")
library(JuliaCall)
julia_command("Threads.nthreads()")
# On Mac this returns 2
# On Windows this returns 1

On my Mac machine (that's why there is a JULIA_HOME line, this works all well, but on my Windows machine JuliaCall always only uses a single thread. Is there some other way to set the number of threads on Windows that I am not aware of?

[e-kotov]

Same here.

@enweg are you admin/root on Windows?

[enweg]

@e-kotov Unfortunately not on the Windows machine. Does it work with admin/root rights?

[e-kotov]

@enweg at the moment I only have access to a Windows machine where I do not have admin rights, so I cannot test.

[pteridin]

Can reproduce. Though, setting the JULIA_NUM_THREADS globally as an admin works and setting JULIA_NUM_THREADS locally using the command line is a workaround too:

Open command line and set the number of threads, then open RStudio using the console:

set JULIA_NUM_THREADS=8
RStudio

Result:

> library(JuliaCall)
Warning message:
package ‘JuliaCall’ was built under R version 4.3.2 
> julia_command("Threads.nthreads()")
Julia version 1.10.0 at location C:\Users\xyz\.julia\juliaup\julia-1.10.0+0.x64.w64.mingw32\bin will be used.
Loading setup script for JuliaCall...
Finish loading setup script for JuliaCall.
8

It would still be useful to be able to use Sys.setenv(JULIA_NUM_THREADS = 2) or set the number of threads as a parameter to julia_setup.

[edwardlavender]

These are two work arounds on Windows that worked for me:

Use set JULIA_NUM_THREADS (as described above)

Launch CMD as administrator, set JULIA_NUM_THREADS in CMD and launch R/RStudio from the same CMD session:

In CMD:

set JULIA_NUM_THREADS = 4
cd "C:\Program Files\RStudio"
rstudio.exe

Then in R:

> library(JuliaCall)
> julia_command("Threads.nthreads()")
Julia version 1.6.7 at location C:\Users\Ian\AppData\Local\Programs\JULIA-~1.7\bin will be used.
Loading setup script for JuliaCall...
Finish loading setup script for JuliaCall.
4

This only works if you launch CMD as an administrator and if the environment variable JULIA_NUM_THREADS is set in the environment from which the Julia application starts (hence, the need to launch R/RStudio from the same CMD session).

Set system-wide environment variables

To set JULIA_NUM_THREADS for all Julia sessions:

• Open the Start menu and search for "Environment Variables".
• Select "Edit the system environment variables".
• In the System Properties window, in the Advanced pane, click on the "Environment Variables" button.
• In the Environment Variables window, under "System variables", click "New".
• Set the variable name to JULIA_NUM_THREADS and the value as required.
• OK everything and close the windows.

Now you can launch R/RStudio in the usual way (e.g., via an application shortcut).

Then in R:

> library(JuliaCall)
> julia_command("Threads.nthreads()")
Julia version 1.6.7 at location C:\Users\Ian\AppData\Local\Programs\JULIA-~1.7\bin will be used.
Loading setup script for JuliaCall...
Finish loading setup script for JuliaCall.
4

[pteridin]

As mentioned before: The workaround as admin does work. Thank you for providing detailled instructons @edwardlavender

Though it would be still nice to set the number of threads without admin rights and on a per-analysis basis. I am currently working on a multi user system environment where it would be sometimes beneficial to do some parallel number crunching on a bunch of CPU cores, but most of the time it would just be enough to use 1-4 cores.

[MateusMaiaDS]

Just to add a remark for anyone who may use the solution provided by edwardlavender in this issue:

If you're using it through the CMD, remember to type:

set JULIA_NUM_THREADS=4

—without any whitespace around the equal sign. Also, make sure to run the CMD as an administrator.