nice, go-idiomatic way of using a shared map

nice, go-idiomatic way of using a shared map

Say I had a program with concurrent access to a map, like this:
func getKey(r *http.Request) string { ... }
values := make(map[string]int)
http.HandleFunc("/get", func(w http.ResponseWriter, r *http.Request) {
key := getKey(r)
fmt.Fprint(w, values[key])
})
http.HandleFunc("/set", func(w http.ResponseWriter, r *http.Request) {
key := getKey(r)
values[key] = rand.Int()
})
This is bad since map writes are non-atomic. So I could use a read/write
mutex
func getKey(r *http.Request) string { ... }
values := make(map[string]int)
var lock sync.RWMutex
http.HandleFunc("/get", func(w http.ResponseWriter, r *http.Request) {
key := getKey(r)
lock.RLock()
fmt.Fprint(w, values[key])
lock.RUnlock()
})
http.HandleFunc("/set", func(w http.ResponseWriter, r *http.Request) {
key := getKey(r)
lock.Lock()
values[key] = rand.Int()
lock.Unlock()
})
Which seems fine except for the fact that we're directly using mutexes and
not channels.
What's a more go-idiomatic way of implementing this? Or is this one of
those times where a mutex is really all you need?