Here's the mutex source: https://golang.org/src/sync/mutex.go . The fast path is...

millstone on July 12, 2015 | parent | context | favorite | on: Singleton Pattern in Go

Here's the mutex source: https://golang.org/src/sync/mutex.go . The fast path is just a CAS, which of course is going to be fast. But it's also important to know how it performs under contention.