Simple yet annoying demonstration of concurrency stuffs in Go

coffee_machines.go

package main

import (
	"fmt"
	"log"
	"sync"
	"time"
)

func main() {
	withMachine := Machines{}

	orders := make(chan int, 12)
	for i := 0; i < 12; i++ {
		go withMachine.makeCoffee(orders, i+1)
	}

	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)
	fmt.Println("Order completed for order no.", <-orders)

	fmt.Println("Espresso machine, time used:", withMachine.EspressoMachine.TimeUsed)
	fmt.Println("Beans grinder, time used:", withMachine.BeansGrinder.TimeUsed)

}

type EspressoMachine struct {
	sync.Mutex
	InUse bool
	TimeUsed int
}

type BeansGrinder struct {
	sync.Mutex
	InUse bool
	TimeUsed int
}

type Machines struct {
	BeansGrinder
	EspressoMachine
}

func (m *Machines) makeCoffee(orders chan int, number int) {
	log.Printf("Got order number %d\n", number)

	var wg sync.WaitGroup
	wg.Add(3)

	prepare := make(chan bool, 2)

	go prepareGlass(wg, prepare, number)
	go m.BeansGrinder.roastBeans(wg, prepare, number)
	<-prepare
	<-prepare
	close(prepare)

	go m.EspressoMachine.makeEspresso(wg, number)

	orders <- number
	wg.Wait()
}

func prepareGlass(wg sync.WaitGroup, status chan bool, number int) {
	log.Printf("Preparing glass for order no. %d\n", number)
	time.Sleep(time.Second*1)

	wg.Done()
	status <- true
}

func (b *BeansGrinder) roastBeans(wg sync.WaitGroup, status chan bool, number int) {
	b.Lock()
	defer b.Unlock()

	log.Printf("Roasting beans for order no. %d\n", number)

	b.InUse = true
	time.Sleep(time.Second*2)
	b.InUse = false

	b.TimeUsed++

	wg.Done()
	status <- true
}

func (e *EspressoMachine) makeEspresso(wg sync.WaitGroup, number int) {
	e.Lock()
	defer e.Unlock()

	log.Printf("Making espresso for order no. %d\n", number)

	e.InUse = true
	time.Sleep(time.Second*3)
	e.InUse = false

	e.TimeUsed++

	wg.Done()
}