[itamarst]

Fixes #299

• Test and fix that makes PERF Limit OpenMP and BLAS in threaded backend as well joblib#1871 (comment) pass

[itamarst]

Plausibly there's a second half missing, where the top-level restore of threadpoolctl, the one where it relinquishes control, should always be to the original level of the process, because when it grabs the original level it might grab the wrong one as a race condition.

[itamarst]

Or, another way of saying it, if thread A stores values to restore to at a time when thread B is the controlling thread, the restore value is wrong, and should instead be "all cores" (zero? or a level stored at startup). Will do that or equivalent tomorrow.

[itamarst]

The above is a real race condition (I have implemented a test and fix) but it is still not enough to fix the joblib race condition reproducer!

[itamarst]

Will continue trying to figure out the joblib race condition next week.