Demonstrates that heavy cpu functions steal time from IO goroutines

heavy_cpu_goroutines_and_http_mux.go

package main

import (
	"fmt"
	"time"
	"net/http"
	"net"
)

const N = 300
const P = 20
const timeFormat = "15:04:05.0000"

func heavy(res chan<- string) {
	start := time.Now()
	var sum int64 = 0
	for i1 := 0; i1 < N; i1++ {
		for i2 := 0; i2 < N; i2++ {
			for i3 := 0; i3 < N; i3++ {
				for i4 := 0; i4 < N; i4++ {
					sum++
				}
			}
		}
	}
	n := int64(N)
	n = n * n
	n = n * n
	if sum != n {
		fmt.Println("Ooops")
	}
	end := time.Now()
	dur := end.Sub(start)
	res <- fmt.Sprintf("started %s, ended %s (lasted %f)", start.Format(timeFormat), end.Format(timeFormat), dur.Seconds())
}

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		str := fmt.Sprintf("The time is %s", time.Now().String())
		w.Write(([]byte)(str))
	})
	listener, _ := net.Listen("tcp", "localhost:7777")
	go http.Serve(listener, mux)

	res := make(chan string, P)
	for i := 0; i < P; i++ {
		go heavy(res)
	}
	fmt.Println(">>>")
	for {
		fmt.Println(<-res)
		go heavy(res)
	}
}