Thank you very much, Quinn,
We need to set the thread priority for our streaming engine.
Our unit tests are testing its modules - beneath other things - with all kinds of (unrealistic) sample rates. And it tries to set thread priorities for standard sample rates like 44.1kHz, 48kHz, ..., 192kHz, etc. while setting up the streaming engine to run on block sizes from 1 sample to something like 16384, which means the thread needs to be set up for computation down to every 1/44100, 1/192000 sec, etc.
IIRC setting the thread_policy below 4/44100 fails.
Although this is (for our current tasks) not a very realistic scenario, I think it should work, at least I would like to know how low the unit tests can go, or even better be able to ask the specific machine about its valid thread_policy range.