get_max_threads returns an upper bound on the number of threads used for subsequent OpenMP parallel regions.

For full information please refer to the NAG Library document for x06ac

https://www.nag.com/numeric/nl/nagdoc_28.7/flhtml/x06/x06acf.html

Returns
ntmaxint

The returned upper bound on the number of threads used for subsequent OpenMP parallel regions.

Notes

get_max_threads, for multithreaded 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.

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 References for a full description of how the number of threads is chosen for a particular parallel region.

In serial implementations of the NAG Library this function will always return . See the X06 Introduction for a discussion of the behaviour of these functions when called in serial.

References

The OpenMP API Specification for Parallel Programming

Chapman, B, Jost, G and van der Pas, R, 2008, Using OpenMP Portable Shared Memory Parallel Programming, The MIT Press