OMP_DYNAMIC

export OMP_DYNAMIC=value

setenv OMP_DYNAMIC value

The OMP_DYNAMIC environment variable enables or disables dynamic adjustment of the number of threads available for execution of parallel regions. The value must be either TRUE or FALSE. The default value is FALSE.

If the value is set to FALSE, dynamic adjustment is disabled. If the value is set to TRUE, the number of threads that are used for executing parallel regions may be adjusted by the runtime environment to best utilize system resources.

OMP_NESTED

export OMP_NESTED=value

setenv OMP_NESTED value

The OMP_NESTED environment variable enables or disables nested parallelism. Its value must be TRUE or FALSE.

If the value is set to TRUE, nested parallelism is enabled and if the value is set to FALSE, the nested parallelism is disabled. The default value is FALSE.

Runtime Library Functions in OpenMP

The OpenMP library functions are external functions. The header <omp.h> declares three types of functions:

•Several functions that can be used to control and query the parallel execution environment.

•Lock functions that can be used to synchronize access to data.

•Timing functions that support a wall-clock timer.

Description of library functions are divided into the following topics:

•Execution Environment Functions

•Lock Functions

•Timing Functions

Execution Environment Functions

The execution environment functions affect and monitor threads, processors, and the parallel environment. This section discusses the following environment functions:

•omp_set_num_threads

•omp_get_num_threads

•omp_get_max_threads

•omp_get_thread_num

•omp_get_num_procs

•omp_in_parallel

•omp_set_dynamic

•omp_get_dynamic

•omp_set_nested

•omp_get_nested

170 Exception Handling