busy_server.go

package main

import (
	"log"
	"net/http"
	"sync/atomic"
	"time"
)

var isBusy int32

const (
	// FREE is the status that server is free
	FREE = 0

	// BUSY is the status that server is busy
	BUSY = 1
)

func HandleSync() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		status := atomic.LoadInt32(&isBusy)
		ctx := r.Context()
		if status == FREE {
			atomic.StoreInt32(&isBusy, 1)
			defer func() {
				atomic.StoreInt32(&isBusy, 0)
			}()

			select {
			case <-time.After(10 * time.Second):
				w.WriteHeader(200)
				w.Write([]byte(`Working...`))
			case <-ctx.Done():
				err := ctx.Err()
				log.Println("context is fired: ", err)
				http.Error(w, err.Error(), http.StatusInternalServerError)
				return
			}

		}
		if status == BUSY {
			w.WriteHeader(http.StatusForbidden)
			w.Write([]byte(`I'm busy`))
		}
	}
}

func main() {
	addr := ":1234"
	r := http.NewServeMux()
	r.Handle("/", HandleSync())

	svr := &http.Server{
		Addr:    addr,
		Handler: r,
	}

	log.Println("server started", addr)
	log.Fatal(svr.ListenAndServe())

}