, 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 routine.
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 routine will always return
See the X06 Chapter Introduction
for a discussion of the behaviour of these routines when called in serial.
Background information to multithreading can be found in the Multithreading
for a demonstration of how to use x06acf