The Daily Walk - Go Concurrency Exercise

main.go

package main

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

var (
	alarmTime     = 60
	rngToGetReady = [2]int{60, 90}
	rngToPutShoes = [2]int{35, 45}
)

func getTime(timeRange [2]int) int {
	// Always re-seed to get non-deterministic generated number.
	// Use UnixNano() instead of Unix() because these methods are called too close to each other,
	// practically being indistinguishable in time delta in seconds. NanoSeconds are not too close
	// though, making its use more suitable here.
	rand.Seed(time.Now().UnixNano())
	// Get a time duration in the given range.
	duration := rand.Intn(timeRange[1]-timeRange[0]+1) + timeRange[0]
	return duration
}

func armAlarm(a chan bool) {
	time.Sleep(time.Duration(60) * time.Second)
	a <- true
}

func main() {
	var wg sync.WaitGroup
	alarm := make(chan bool)
	startTime := time.Now()

	gettingReady := func(name string) {
		fmt.Println(name, "started getting ready.")

		duration := getTime(rngToGetReady)
		time.Sleep(time.Duration(duration) * time.Second)

		fmt.Println(name, "spent", duration, "seconds getting ready.")
		wg.Done()
	}

	putShoe := func(name string) {
		fmt.Println(name, "started putting shoe.")

		duration := getTime(rngToPutShoes)
		time.Sleep(time.Duration(duration) * time.Second)

		fmt.Println(name, "spent", duration, "putting on shoe.")
		wg.Done()
	}

	fmt.Println("Let's go for a walk!")
	wg.Add(2)
	go gettingReady("Alice")
	go gettingReady("Bob")

	wg.Wait()

	fmt.Println("\nArming alarm.\n")
	// Re-add two more "things to wait".
	wg.Add(2)
	go armAlarm(alarm)
	go putShoe("Alice")
	go putShoe("Bob")

	wg.Wait()

	<-alarm
	fmt.Println(time.Now().Sub(startTime))
}