3.8 OMP_NUM_THREADS – Specifies the number of threads to use

Description:

Specifies the default number of threads to use in parallel regions. The value of this variable shall be a comma-separated list of positive integers; the value specified the number of threads to use for the corresponding nested level. If undefined one thread per CPU is used.

See also:

omp_set_num_threads

Reference:

OpenMP specification v4.5, Section 4.2