mutex-counter.go

package main

import (
	"fmt"
	"sync"
	"time"
)

//Safecounter is safe to use concurrently
type SafeCounter struct  {
	v map[string]int
	mux sync.Mutex
}

// Inc increments the counter for the given key
func (c *SafeCounter) Inc(key string) {

	c.mux.Lock()
	// Lock so only one goroutine at a time can access the map c.v.
	c.v[key]++
	c.mux.Unlock()
}

// value returns the current value of the counter for the given key
func (c *SafeCounter) Value(key string) int {
	c.mux.Lock()
	//Lock so only one goroutine at a time can access the map c.v
	defer c.mux.Unlock()
	return c.v[key]
}

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

		go c.Inc("somekey")
	}

	time.Sleep(time.Second)
	fmt.Println(c.Value("somekey"))
}