[Octave-bug-tracker] [bug #51643] setting OMP_NUM_THREADS at runtime does not chaneg number of openmp threads

[Carnë Draug]

Follow-up Comment #3, bug #51643 (project octave):

> I suspect that there was a misunderstanding at some point about how this
environment variable works. So instead of checking the value each time an
OMP-enabled function is called, it is only checked once to set some global
variable to specify the thread limit?

Yes. When a program starts, there's a set of environment variables that are
read. They are never read again.  Instead, if a program wants to change them,
there's a set of functions to use:

http://pages.tacc.utexas.edu/~eijkhout/pcse/html/openmp.html#Runtimefunctionsandinternalcontrolvariables

> I hesitate to intercept and do special things for specific variables in
Octave's putenv function.
>
> Maybe we should document that the initial value of the number of threads may
be set from the environment and also offer a separate function to set the
thread limit for OMP? 

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