Sync.Mutex

package main

import (
    "fmt"
)

type SafeCounter struct {
    v  map[string]int
}

func (c *SafeCounter) Inc(key string) {
    c.v[key]++
}

func (c *SafeCounter) Value(key string) int {
    return c.v[key]
}

func main() {
    c := SafeCounter{v: make(map[string]int)}
    for i := 0; i < 1000; i++ {
        go c.Inc("somekey")
    }

    fmt.Println(c.Value("somekey"))
}