count.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"sync"
)

type counter struct {
	sync.Mutex
	count uint64
}

func (c *counter) inc() uint64 {
	c.Lock()
	defer c.Unlock()

	cur := c.count
	c.count++
	return cur
}

func main() {
	var c counter

	http.HandleFunc("/inc", func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintf(w, "%d", c.inc())
	})

	log.Printf("starting server on 8080")
	log.Fatal(http.ListenAndServe(":8080", nil))
}