NAG CL Interface
x06acc (get_​max_​threads)

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1 Purpose

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

2 Specification

#include <nag.h>
Integer  x06acc ()
The function may be called by the names: x06acc or nag_omp_get_max_threads.

3 Description

x06acc, 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. 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 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

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

5 Arguments


6 Error Indicators and Warnings


7 Accuracy

Not applicable.

8 Parallelism and Performance

Background information to multithreading can be found in the Multithreading documentation.
x06acc is not threaded in any implementation.

9 Further Comments


10 Example

See x06aac for a demonstration of how to use x06acc.