3.1.9 omp_set_nested Function

The omp_set_nested function enables or disables nested parallelism. The format is as follows:

#include <omp.h>
void omp_set_nested(int nested);

If nested evaluates to 0, nested parallelism is disabled, which is the default, and nested parallel regions are serialized and executed by the current thread. If nested evaluates to a nonzero value, nested parallelism is enabled, and parallel regions that are nested may deploy additional threads to form nested teams.

This function has the effects described above when called from a portion of the program where the omp_in_parallel function returns zero. If it is called from a portion of the program where the omp_in_parallel function returns a nonzero value, the behavior of this function is undefined.

This call has precedence over the OMP_NESTED environment variable.

When nested parallelism is enabled, the number of threads used to execute nested parallel regions is implementation-defined. As a result, OpenMP-compliant implementations are allowed to serialize nested parallel regions even when nested parallelism is enabled.

Cross References:

• OMP_NESTED environment variable, see Section 4.4 on page 49.

• omp_in_parallel function, see Section 3.1.6 on page 38.