>>>>> Dirk Eddelbuettel writes: > On 23 May 2024 at 20:02, Ivan Krylov wrote: > | On Wed, 22 May 2024 09:18:13 -0500 > | Dirk Eddelbuettel <e...@debian.org> wrote: > | > | > Testing via 'nm' as you show is possible but not exactly 'portable'. > | > So any suggestions as to what to condition on here? > | > | (My apologies if you already got an answer from Kurt. I think we're not > | seeing his mails to the list.) > | > | Perhaps take the configure test a bit further and try to dyn.load() the > | resulting shared object? To be extra sure, call the function that uses > | the OpenMP features? (Some weird systems may have lazy binding enabled, > | making dyn.load() succeed but crashing the process on invocation of a > | missing function.) > | > | On GNU/Linux, the linker will happily leave undefined symbols in when > | creating a shared library (unlike on, say, Windows, where extern void > | foo(void); foo(); is a link-time error unless an object file or an > | import library providing foo() is also present). When loading such a > | library, the operation fails unless the missing symbols are already > | present in the address space of the process (e.g. from a different > | shared library). > | > | A fresh process of R built without OpenMP support will neither link in > | the OpenMP runtime while running SHLIB nor have the OpenMP runtime > | loaded and so should successfully fail the test. > | > | I also wouldn't call the entry point "main" just in case some future > | compiler considers this a violation of the rules™ [*] and breaks the > | code. extern "C" void configtest(int*) would be compatible with .C() > | without having to talk to R's memory manager: > | > | # The configure script: > | cat > test-omp.cpp <<EOF > | #include <omp.h> > | extern "C" void configtest(int * arg) { > | *arg = omp_get_num_threads(); > | } > | EOF > | # Without the following you're relying on the GNU/Linux-like behaviour > | # w.r.t. undefined symbols (see WRE 1.2.1.1): > | cat > Makevars <<EOF > | PKG_CXXFLAGS = \$(SHLIB_OPENMP_CXXFLAGS) > | PKG_LIBS = \$(SHLIB_OPENMP_CXXFLAGS) > | EOF > | R CMD SHLIB test-omp.cpp > | > | # And then in R: > | dyn.load(paste0("test-omp", .Platform$dynlib.ext)) > | # There's probably no need to test the return value, right? > | .C("configtest", arg = integer(1))$arg
That seems a very nice way of following WRE's If you do use your own checks, make sure that OpenMP support is complete by compiling and linking an OpenMP-using program Modulo not hard-wiring 'R' in the configure code, and instead doing the usual : ${R_HOME=`R RHOME`} if test -z "${R_HOME}"; then echo "could not determine R_HOME" exit 1 fi "${R_HOME}/bin/R" CMD SHLIB ..... etc. Best -k > Given that comes from RcppArmadillo we can rely on Rcpp::cppFunction() or > Rcpp::sourceCpp() which should make that dance a little simpler. > I had forgotten this was in fact a home-grown shell snippet (per `git blame` > last polished by Kevin, now CC'ed, in 2020). That should make an explicit > load -- and noticing when we fail to load -- feasible. > Maybe someone has time and appetite for contributing a PR? > Cheers, Dirk > | -- > | Best regards, > | Ivan > | > | [*] > | In C++, main() is the function-that-must-not-be-named: > | https://en.cppreference.com/w/cpp/language/main_function > -- > dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org ______________________________________________ R-package-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-package-devel