Clarifying the status of OMP in CRAN binaries on Mac

It is possible to compile, say mgcv with OpenMP. There are several steps (done on a Mac M4 with Sequoia 15.3.2) :

- Installed R 4.5.0 patched (should not change from the initial 4.5.0 version, but to be correct)

- Installed the compilation tools with `xcode-select ?install`

- Installed gfortran-14.2-universal.pkg from here: https://mac.r-project.org/tools/

- Followed instructions here: https://mac.r-project.org/bin/, that is, `sudo R`, then `source("https://mac.R-project.org/bin/install.R ?)`, then

```bash
install.libs("r-base-dev")
install.libs("gettext")
```

- Followed instructions on this page to get experimental OpenMP libraries: https://mac.r-project.org/openmp/

- Downloaded the latest .tar.gz source of mgcv and placed the file in the current directory

- Recompiled mgcv with: `PKG_CPPFLAGS='-Xclang -fopenmp' PKG_LIBS=-lomp R CMD INSTALL mgcv-1.9-3.tar.gz`

Now I have `mgcv:::mgcv.omp()` that returns TRUE.

Note that I used to recompile data.table also to get a multithreaded version, but apparently, it is not needed any more:

```R
install.packages("data.table")
library(data.table)
getDTthreads() # 8 for me by default (M4 max)
packageVersion("data.table") # 1.17.0
```

It would be nice to get multithreading, and especially OpenMP, enabled by default for the Mac. But I understand that it is risky since Apple does not support it officially.

Best,

Philippe

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( ( ( ( (    Prof. Philippe Grosjean
 ) ) ) ) )
( ( ( ( (    Numerical Ecology
 ) ) ) ) )   Mons University, Belgium
( ( ( ( (
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Le 24 avr. 2025 ? 11:58, Gavin Simpson <ucfagls at gmail.com> a ?crit :

Dear list,

I'm trying to clarify my understanding of what is and is not
implemented / expected in terms of openMP support in R and CRAN
package *binaries* for MacOS on apple silicon.

I have the CRAN's R binary for MacOS X (apple silicon) and also the
CRAN binaries for two packages, glmmTMB and mgcv, both of which seem
to be instrumented (following WRE) to use OpenMP if available. And
from discussions here I understand that thanks to Simon and  others,
OpenMP support for MacOS X is in R and so should I expect OpenMP to
work in these two packages?

If I am, neither of them is working on various of my Mac systems;
model fitting is single threaded and the test functions that glmmTMB
and mgcv use to detect OMP support both return FALSE:

R version 4.5.0 (2025-04-11) -- "How About a Twenty-Six"
Platform: aarch64-apple-darwin20 (64-bit)
r$> glmmTMB::omp_check()
[1] FALSE
r$> mgcv:::mgcv.omp()
[1] FALSE

Is this reproducible on other's systems? (Could someone run those two
bits of code on their systems if they use the MacOS X R binary from
CRAN and the CRAN Mac binaries for the packages - running mgcv's test
should be easier as this pkg is shipped with the R binary).

I am happy to provide further system details, but at this point I'm
mostly hoping to clarify what I should expect and whether what I'm
seeing is typical?

Thanks in advance

Gavin

--
Gavin Simpson, PhD [he/him/his]
[tw] @ucfagls [OrciD] 0000-0002-9084-8413
[web] fromthebottomoftheheap.net
? Assistant Professor
? Department of Animal & Veterinary Sciences, Aarhus University
? Adjunct Professor, Department of Biology, University of Regina.