count_server.go

// Server2 is a minimal "echo" and counter server.
package main

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

var mu sync.Mutex
var count int

func main() {
	// strangely, when I first tried this it would call
	// "handler" TWICE every time I did http://localhost:8000 in browser,
	// increasing count twice. it would also call both
	// "counter" AND "handler" every time I did http://localhost:8000/count,
	// increasing count by 1 for /count.

	// http://localhost:8000 should only increase count by 1
	// http://localhost:8000/count should NOT change count at all

	// now it works fine, but what went wrong? (mutex has nothing to do with the error)

	http.HandleFunc("/", handler)
	http.HandleFunc("/count", counter)
	log.Fatal(http.ListenAndServe("localhost:8000", nil))
}

// handler echoes the Path component of the requested URL.
func handler(w http.ResponseWriter, r *http.Request) {
	mu.Lock()
	count++
	fmt.Println("in handler")
	fmt.Fprintf(w, "Increment Count %d\n", count)
	mu.Unlock()
	fmt.Fprintf(w, "URL.Path = %q\n", r.URL.Path)
}

// // counter echoes the number of calls so far.
func counter(w http.ResponseWriter, r *http.Request) {
	fmt.Println("in counter")
	mu.Lock()
	fmt.Fprintf(w, "Count %d\n", count)
	mu.Unlock()
}

//!-