[R-pkg-devel] Setting OpenMP threads (globally) for an R package

Evan,

honestly, I think your request may be a red herring. Threads typically
don't cause memory explosion, because OpenMP threads don't allocate new
memory, but uncontrolled forking does. There are many things that are not
allowed inside mclapply so that's where I would look. It may be better to
look at the root cause first, but for that we would need more details on
what you are doing.

Cheers,
Simon

On Mar 18, 2022, at 2:51 AM, Evan Biederstedt <

evan.biederstedt at gmail.com> wrote:

Hi R-package-devel

I'm developing an R package which uses `parallel::mclapply` and several
other library dependencies which possibly rely upon OpenMP.

Unfortunately,

some functions explode the amount of memory used.

I've noticed that if I set `export OMP_NUM_THREADS=1` before starting R,
the memory is far more manageable.

My question is, if there a way for me to achieve this behavior within

the R

package itself?

My initial try was to use `R/zzz.R` and an `.onLoad()` function to load
these global variables upon loading the library.

```
.onLoad <- function(libname, pkgname){
 Sys.setenv(OMP_NUM_THREADS=1)
}
```

But this doesn't work. The memory still explodes. In fact, I'm worried

that

this cannot be done within an R package itself, as R has already started,
e.g.  https://stackoverflow.com/a/27320691/5269850

Is there a recommended approach for this problem when writing R packages?

Package here: https://github.com/kharchenkolab/numbat

Related question on SO:

https://stackoverflow.com/questions/71507979/set-openmp-threads-for-all-dependencies-in-r-package

Any help appreciated. Thanks, Evan

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