GRASS and OpenMP

[dhdeangelis]

Following a comment by @metzm in an issue:

The reason why r.patch recently (since about 5 months ago) fails with a large number of input maps is #5731 merged on June 13 2025 which changed the default number of threads from 1 to the OpenMP default thread count.

(#6615 (comment))

I wonder if OpenMP should be manually set before running GRASS or, in this case for example, r.patch. I have OpenMP installed but the environmental variable OMP_NUM_THREADS is not set. This apparently is leading to some problems. I see the relevant chapter in OpenMP manual (https://www.openmp.org/spec-html/5.0/openmpse50.html) but I am not completely at home in these matters.

Any hint on how to best deal with this will be appreciated.

[wenzeslaus]

You can set the number of cores/processes/threads for each call of a tool individually with nprocs or you can limit the number of threads specifically for OpenMP with the variable. Is this what you are after?