Some environments don't have a scheduler or a "user-space", and so this implementation can suffice, but the problem with this post is that all of the testing and benchmarking are done in user-space, and hence the metrics are not very meaningful.

But more importantly, even with kernel backed waiting (e.g. using futexes) some userspace spinning can be important for performance. And then pretty much all the concerns from the spinlock apply there as well.