The function is osunfairlockwithoptions() and the options I used are OSUNFAIRLOCKDATASYNCHRONIZATION and OSUNFAIRLOCKADAPTIVESPIN
The latter asks the kernel to use kernel-space adaptive spinning, and the former prevents it from spawning additional threads in the thread pools used by Apple's libraries
Did they work? Yes! Performance on lightly loaded systems was about the same as OSSpinLock, but on loaded ones, they provided massively better responsiveness
I initially fell back to OSSpinLock as an intermediate solution on older systems. Later I managed to get rid of it for good by relying on osunfairlock plus manual spinning in user space