OMP_NESTED – Nested parallel regions ¶Enable or disable nested parallel regions, i.e., whether team members
are allowed to create new teams. The value of this environment variable
shall be TRUE or FALSE. If set to TRUE, the number
of maximum active nested regions supported will by default be set to the
maximum supported, otherwise it will be set to one. If
OMP_MAX_ACTIVE_LEVELS is defined, its setting will override this
setting. If both are undefined, nested parallel regions are enabled if
OMP_NUM_THREADS or OMP_PROC_BINDS are defined to a list with
more than one item, otherwise they are disabled by default.
Note that the OMP_NESTED environment variable was deprecated in
the OpenMP specification 5.2 in favor of OMP_MAX_ACTIVE_LEVELS.
omp_set_max_active_levels – Limits the number of active parallel regions, omp_set_nested – Enable/disable nested parallel regions,
OMP_MAX_ACTIVE_LEVELS – Set the maximum number of nested parallel regions
OpenMP specification v4.5, Section 4.6