[R] Number of Cores limited to two in CRAN

[Henrik Bengtsson]

Short answer: You don't want to override that limit in your R package.
Don't do it.

Long answer: You'll find the reason for this in the 'CRAN Repository
Policy' (https://cran.r-project.org/web/packages/policies.html).
Specifically, the following passage:

"Checking the package should take as little CPU time as possible, as
the CRAN check farm is a very limited resource and there are thousands
of packages. Long-running tests and vignette code can be made optional
for checking, but do ensure that the checks that are left do exercise
all the features of the package.

**If running a package uses multiple threads/cores it must never use
more than two simultaneously: the check farm is a shared resource and
will typically be running many checks simultaneously.**

Examples should run for no more than a few seconds each: they are
intended to exemplify to the would-be user how to use the functions in
the package."

Basically, you can use two cores to demonstrate or validate (e.g. in
package tests) that your code *can* run in parallel, but you must not
use more than that to demonstrate that your code can "run super fast".

Even-longer answer: See my blog post 'Please Avoid detectCores() in
your R Packages' (https://www.jottr.org/2022/12/05/avoid-detectcores/)
from 2022-12-05 for even more reasons.

/Henrik

On Sun, Jul 2, 2023 at 9:55 AM Ravi Varadhan via R-help
<r-help using r-project.org> wrote:
>
> This is the specific error messsage from R CMD check --as-cran
>
>
> Error in .check_ncores(length(names)) : 16 simultaneous processes spawned
>   Calls: prepost -> makeCluster -> makePSOCKcluster -> .check_ncores
>   Execution halted
>
>
> Thanks,
> Ravi
>
> ________________________________
> From: Ravi Varadhan
> Sent: Saturday, July 1, 2023 1:15 PM
> To: R-Help <r-help using r-project.org>
> Subject: Number of Cores limited to two in CRAN
>
> Hi,
> I am developing a package where I would like to utilize multiple cores for parallel computing.  However, I get an error message when I run R CMD check --as-cran.
>
> I read that CRAN limits the number of cores to 2.  Is this correct? Is there any way to overcome this limitation?
>
> Thank you,
> Ravi
>
>         [[alternative HTML version deleted]]
>
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