$ man -k spin
pthread_spin_destroy (3) - initialize or destroy a spin lock
pthread_spin_init (3) - initialize or destroy a spin lock
pthread_spin_lock (3) - lock and unlock a spin lock
pthread_spin_trylock (3) - lock and unlock a spin lock
pthread_spin_unlock (3) - lock and unlock a spin lock
TAP::Parser::Scheduler::Spinner (3perl) - A no-op job.
Not to mention that ~95% of the Earth's population doesn't speak English as the first language, how stuff is named in English is not obvious. Bad search engines, like what `man -k` has, are nearly unusable if you don't know the exact term. You'd laugh when people would recommend to you to look up words using a paper dictionary or write papers using paper encyclopedias but `man -k` is pretty much that.
It makes total sense to those who know it by heart, but at the same time it makes no sense to those who honestly don't. The line between is pretty hard.
Also, this is what makes me believe there is room for more discoverability-commands in Linux-land CLI. Especially for diagnostics. Since those developing it have a hard time seeing the same from a beginner point of view.
https://www.google.com/search?q=linux+spin+lock+library
pthread_spin_lock(3) is on the first page, along with a RH presentation which explains exactly why trying to roll your own userspace implementation is unlikely to be successful. The guy simply didn't do his homework, I have no idea why you are trying to defend him.
I wonder everyday how I teach my colleuges how they should learn more about linux. My best attempt so far is to skim the man pages of at least coreutils rpm. That and TLDP.
It's like knowing Google Fu, much is in finding useful keywords.