[R-pkg-devel] Request for assistance: error in installing on Debian (undefined symbol: omp_get_num_procs) and note in checking the HTML versions (no command 'tidy' found, package 'V8' unavailable)

[Ivan Krylov]

В Thu, 21 Mar 2024 18:32:59 +0000
Annaig De-Walsche <annaig.de-walsche using inrae.fr> пишет:

> If ever I condition the use of OpenMD directives, users will indeed
> be capable of installing the package, but they wont access to a
> performant version of the code, as it necessitates the use of OpenMD.
> Is there a method to explicitly express that the use of OpenMD is
> highly encouraged?

I think the most practical method would be to produce a
packageStartupMessage() from the .onAttach function of your package if
you detect that the package has been compiled without OpenMP support:
https://cran.r-project.org/doc/manuals/R-exts.html#Load-hooks

> In practical, how to know from R code if OpenMP is present or not?

Your C code will have to detect it and provide this information to the
R code. WRE 1.6.4 says:

>> [C]heck carefully that you have followed the advice in the
>> subsection on OpenMP support [WRE 1.2.1.1]. In particular, any use
>> of OpenMP in C/C++ code will need to use
>> 
>>  #ifdef _OPENMP
>>  # include <omp.h>
>>  #endif

<https://cran.r-project.org/doc/manuals/R-exts.html#Portable-C-and-C_002b_002b-code>

Similarly, any time you use #pragma omp ... or call
omp_set_num_threads(), it needs to be wrapped in #ifdef _OPENMP ...
#endif.

Additionally, it is important to make sure that during tests and
examples, your OpenMP code doesn't use more than two threads:
https://cran.r-project.org/web/packages/policies.html
This is in place because CRAN checks are run in parallel, and a package
that tries to helpfully use all of the processor cores would interfere
with other packages being checked at the same time.

> 	[[alternative HTML version deleted]]

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-- 
Très cordialement,
Ivan