User's Guide

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