sync.RWMutexを使おう ref: http://qiita.com/y_matsuwitter/items/36565a3a53ac52732cae

file1.txt

$ go run rwmutex.go
read_start
read_start
write_start
read_start
read_complete fuga
read_complete fuga
write_complete
read_complete piyo

rwmutex.go

package main

import (
    "sync"
    "time"
)

var mu sync.RWMutex
var data map[string]string

func main() {
    data = map[string]string{"hoge": "fuga"}
    mu = sync.RWMutex{}
    go read()
    go read()
    go write()
    go read()
    time.Sleep(5 * time.Second)
}

func read() {
    println("read_start")
    mu.RLock()
    defer mu.RUnlock()
    time.Sleep(1*time.Second)
    println("read_complete", data["hoge"])
}

func write() {
    println("write_start")
    mu.Lock()
    defer mu.Unlock()
    time.Sleep(2 * time.Second)
    data["hoge"] = "piyo"
    println("write_complete")
}