Implementation of #1 exercise on http://whipperstacker.com/2015/10/05/3-trivial-concurrency-exercises-for-the-confused-newbie-gopher

daily_walk.go

package main

import (
	"fmt"
	"math/rand"
	"sync"
	"time"
)

var wg sync.WaitGroup

func main() {
	done := make(chan bool)
	rand.Seed(time.Now().UTC().UnixNano())

	wg.Add(2)
	go getReady("Alice")
	go getReady("Bob")
	wg.Wait()

	wg.Add(1)
	go armAlarm()
	go putShoes("Alice", done)
	go putShoes("Bob", done)

	for i := 0; i < 2; i++ {
		<-done
	}

	fmt.Println("Exiting and locking the door.")

	wg.Wait()
}

func getReady(person string) {
	wait := randomize(6, 9)
	fmt.Println(fmt.Sprintf("%s started getting ready", person))
	time.Sleep(time.Duration(wait) * time.Second)
	fmt.Println(fmt.Sprintf("%s spent %d seconds getting ready", person, wait))
	wg.Done()
}

func putShoes(person string, done chan bool) {
	wait := randomize(3, 4)
	fmt.Println(fmt.Sprintf("%s started putting shoes", person))
	time.Sleep(time.Duration(wait) * time.Second)
	fmt.Println(fmt.Sprintf("%s spent %d seconds putting shoes", person, wait))
	done <- true
}

func armAlarm() {
	fmt.Println("Arming alarm.")
	time.Sleep(10 * time.Millisecond)
	fmt.Println("Arming is counting down.")
	time.Sleep(5 * time.Second)
	fmt.Println("Alarm armed.")
	wg.Done()
}

func randomize(min, max int) int {
	return min + rand.Intn(max)
}