USE flag threads... pthreads, openmp

[neyuru]

In my system, several packages have the option to select the threads USE flag:

"Add threads support for various packages. Usually pthreads"

But I also use linear algebra libraries (e.g. OpenBLAS) through the eselect-ldso USE flag. In Gentoo's wiki page it is warned:

"Don’t use pthread and openmp at the same time since it will incur significant performance drop due to excessive thread creation.
This can happen when some libraries linked against an application use OpenMP threading, while some others use pthread."

I don't seem to find a way to control what threading paradigm the programs use (when the threads USE flag is ON) so it is a possibility that they are defaulted to pthreads. On the other side, OpenBLAS might be using openmp, clearly violating the warning in the wiki page. If I'm not mistaken, threads will enable multithreaded support on packages that have the option of doing so through USE flag threads. If so, I wouldn't want to miss that feature by forcefully disabling the threads USE flag so that OpenBLAS lives happily in my system (I do prioritize this math library over anything else)

Any thoughts????