> Mutex, or MUTual EXclusion, in Go is basically a way to make sure that only one goroutine is messing with a shared resource at a time. This resource can be a piece of code, an integer, a map, a struct, a channel, or pretty much anything.

This is untrue right? It can only protect code, not data, right?

I have misgivings about such long spinlocks in user space. A millisecond is over a million instructions.