[R-pkg-devel] Default number of cores <=2

[Uwe Ligges]

On 09.02.2020 09:56, Murray Efford wrote:
> The CRAN Repository Policy (revision 4170) states "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" and I try to respect this limit in package example code. However I was recently warned that package functions must not default to >2 cores, even if checks are limited to 2 cores. I see the sense in this, to not hog resources on multi-user systems, but I cannot find it in the documentation. My package 'secr' has unintentionally violated such a policy since October (multithreading with RcppParallel in function 'secr.fit'). No complaints so far, but I'd like to dodge the pain of rejection at my next revision.
> 
> Further, "not all CRAN machines use _R_CHECK_LIMIT_CORES_", so that environment variable cannot be relied upon to apply a 2-core limit during checking.


You  found it: The cited CRAN policies say that you must not use more 
than 2 by default.


> I would appreciate pointers to the relevant documentation and guidance on how others handle this. Is it unavoidable that for users to exploit multiple cores they must specify a non-default function argument, or similar?

Exactly.

Best,
Uwe Ligges


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