Golang Concurrency Exercises #1 http://whipperstacker.com/2015/10/05/3-trivial-concurrency-exercises-for-the-confused-newbie-gopher

morning_routine.go

package main

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

var peopleGroup sync.WaitGroup
var alarmGroup sync.WaitGroup

func random(min, max int64) int64 {
	rand.Seed(time.Now().UTC().UnixNano())
	return rand.Int63n(max-min) + min
}

type Person struct {
	name string
}

type Task struct {
	desc    string
	minTime int64
	maxTime int64
}

func PerformTask(who *Person, task *Task) {
	defer peopleGroup.Done()
	fmt.Printf("%s started %s\n", who.name, task.desc)
	duration := random(task.minTime, task.maxTime)
	time.Sleep(time.Duration(duration) * time.Second)
	fmt.Printf("%s spent %d seconds %s\n", who.name, duration, task.desc)
}

func AlarmTick() {
	defer alarmGroup.Done()
	fmt.Println("Alarm is counting down")
	time.Sleep(60 * time.Second)
	fmt.Println("Alarm is armed")
}

func main() {
	
	getReady := Task{minTime: 60, maxTime: 90, desc: "getting ready"}
	wearShoes := Task{minTime: 35, maxTime: 45, desc: "putting on shoes"}
	
	peopleGroup.Add(2)

	alice := Person{name: "Alice"}
	bob := Person{name: "Bob"}

	fmt.Println("Let's go for a walk")

	go PerformTask(&alice, &getReady)
	go PerformTask(&bob, &getReady)

	peopleGroup.Wait()

	alarmGroup.Add(1)
	fmt.Println("Arming alarm")
	go AlarmTick()

	peopleGroup.Add(2)

	go PerformTask(&alice, &wearShoes)
	go PerformTask(&bob, &wearShoes)

	peopleGroup.Wait()

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

	alarmGroup.Wait()
}