Golang：从带有互斥量的哈希图中读取的最佳方法

This is a continuation from here: Golang: Shared communication in async http server

Assuming I have a hashmap w/ locking:

//create async hashmap for inter request communication
type state struct {
    *sync.Mutex // inherits locking methods
    AsyncResponses map[string]string // map ids to values
}
var State = &state{&sync.Mutex{}, map[string]string{}}

Functions that write to this will place a lock. My question is, what is the best / fastest way to have another function check for a value without blocking writes to the hashmap? I'd like to know the instant a value is present on it.

MyVal = State.AsyncResponses[MyId]

Reading a shared map without blocking writers is the very definition of a data race. Actually, semantically it is a data race even when the writers will be blocked during the read! Because as soon as you finish reading the value and unblock the writers - the value may not exists in the map anymore.

Anyway, it's not very likely that proper syncing would be a bottleneck in many programs. A non-blocking lock af a {RW,}Mutex is probably in the order of < 20 nsecs even on middle powered CPUS. I suggest to postpone optimization not only after making the program correct, but also after measuring where the major part of time is being spent.