Yea, that is a bit inscrutable, but I see mumps is the main/only user of this:

/* if using PETSc OpenMP support, we only call MUMPS on master ranks. Before/after the call, we change/restore CPUs the master ranks can run on */

And I see _OPENMP is a macro for the release date (yyyymm) of the OMP version. It's not clear what the v5.0 is (https://www.openmp.org/specifications/)

{200505,"2.5"},{200805,"3.0"},{201107,"3.1"},{201307,"4.0"},{201511,"4.5"},{201811,"5.0"},{202011,"5.1"}

On Sat, Nov 6, 2021 at 4:27 PM Junchao Zhang <junchao.zhang@gmail.com> wrote:

On Sat, Nov 6, 2021 at 5:51 AM Mark Adams <mfadams@lbl.gov> wrote:

Two questions on OMP:

* Can I test for the version of OMP? I want >= 5 and I see this, which looks promising:

include/petscsys.h:#elif defined(_OPENMP) && _OPENMP >= 201307 && !defined(_WIN32)

* What is the difference between HAVE_OPENMP and 

HAVE_OPENMP_SUPPORT.

# this is different from HAVE_OPENMP. HAVE_OPENMP_SUPPORT checks if we have facilities to support

# running PETSc in flat-MPI mode and third party libraries in MPI+OpenMP hybrid mode

if self.mpi.found and self.mpi.support_mpi3_shm and self.pthread.found and self.hwloc.found:

# Apple pthread does not provide this functionality

if self.function.check('pthread_barrier_init', libraries = 'pthread'):

self.addDefine('HAVE_OPENMP_SUPPORT', 1)

 

Thanks,

Mark