Rethinking the futex API

> And yet here we are with a proposal for futex_waitv() that must always make a syscall, which could be avoid in the uncontested case if it was implemented in user space.

Why must it make a syscall in the uncontested case? It seems to me that it could first try to lock each of the futexes in user space and only make the syscall if none of them were available—much like the current implementation does for a single futex.