> had not heard of anyone actually using a spinlock in production code
Go stdlib sync.Mutex uses spins: https://victoriametrics.com/blog/go-sync-mutex / https://archive.vn/BIb7F
Optimistically spinning for a bit before falling back to futex or equivalent is very different from a spinlock.
Optimistically spinning for a bit before falling back to futex or equivalent is very different from a spinlock.