I was wondering about  that when I saw it but hadn't followed up (too much multitasking).

I think I found the problem, it's day 1. The argument to SetThreadAffinityMask is supposed to be DWORD_PTR,
not a DWORD, so "&affinity_mask" instead of "affinity_mask". It supports 64 CPU by casting the pointer as DWORD64_ptr.

It's all clear now. Thanks for your persistence.