x06 Chapter Contents
x06 Chapter Introduction
NAG Library Manual

# NAG Library Function Documentnag_omp_get_max_threads (x06acc)

## 1  Purpose

nag_omp_get_max_threads (x06acc) returns an upper bound on the number of threads used for subsequent OpenMP parallel regions.

## 2  Specification

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## 3  Description

nag_omp_get_max_threads (x06acc), for multi-threaded implementations, returns the number of the threads to be requested for subsequent parallel regions. The value is the first element of the list held by the OpenMP Internal Control Variable (ICV) used in determining the number of threads. See Users' Note for your implementation for details of the scope of this function.
The number of threads used in parallel regions will be equal to, or less than, the first value of the ICV. The actual number of threads used is dependent on several factors, such as the presence of a num_threads clause on the parallel directive or the number of threads already in use by the program. Please refer to Section 4 for a full description of how the number of threads is chosen for a particular parallel region.
In serial implementations of the NAG C Library this function will always return $1$. See the x06 Chapter Introduction for a discussion of the behaviour of these functions when called in serial.

## 4  References

OpenMP Specifications http://openmp.org/wp/OpenMP-Specifications
Chapman B, Jost G and van der Pas R (2008) Using OpenMP Portable Shared Memory Parallel Programming The MIT Press

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