OMP_NESTED (GNU libgomp)

### 4.10 `OMP_NESTED` – Nested parallel regions ¶

ICV: max-active-levels-var
Scope: data environment
Description:

  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 is by default set to the maximum supported, otherwise it is set to one. If `OMP_MAX_ACTIVE_LEVELS` is defined, its setting overrides 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 5.0 in favor of `OMP_MAX_ACTIVE_LEVELS`.

See also:

  `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

Reference:

  OpenMP specification v4.5, Section 4.6