What does an empty select do?

Question

I found the following code in net/http/httptest and wonder what the empty select statement does in Go.

go s.Config.Serve(s.Listener) if *serve != "" {   fmt.Fprintln(os.Stderr, "httptest: serving on", s.URL)   select {} } 

Answer 1

An empty select{} statement blocks forever. It is similar to an empty for{} statement.

On most (all?) supported Go architectures, the empty select will yield CPU. An empty for-loop won't, i.e. it will "spin" on 100% CPU.