Sleeping Barber Problem

main.go

package main

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

type Barber struct {
	Customer    chan *Customer
	WaitingRoom chan *Customer
	Sleep       chan struct{}
}

func NewBarber(waitingRoomSize int) *Barber {
	b := &Barber{make(chan *Customer, 1), make(chan *Customer, waitingRoomSize), make(chan struct{}, 1)}
	go b.Work()
	return b
}

func (b *Barber) Work() {
	b.Sleep <- struct{}{}
	fmt.Println("[BARBER] Sleeping...zzZ")
	for {
		c := <-b.Customer
		// There is a customer and the chair is empty.
		b.CutHair(c)
		select {
		case c := <-b.WaitingRoom:
			b.Customer <- c
			fmt.Printf("[BARBER] Takes Customer #%d from the waiting room.\n", c.Number)
		default:
			// The Barber is sleeping.
			b.Sleep <- struct{}{}
			fmt.Println("[BARBER] Sleeping...zzZ")
		}
	}
}

func (b *Barber) CutHair(c *Customer) {
	fmt.Printf("[BARBER] CutHair START: Customer #%d\n", c.Number)
	time.Sleep(time.Duration(rand.Intn(1000)) * time.Millisecond)
	fmt.Printf("[BARBER] CutHair  END: Customer #%d\n", c.Number)
}

type Customer struct {
	Number int
}

func NewCustomer(number int) *Customer {
	return &Customer{number}
}

func (c *Customer) WalkIn(b *Barber) {
	fmt.Printf("[CUSTOMER] #%d walks in the shop\n", c.Number)
	select {
	case <-b.Sleep:
		// If the barber is sleeping - wake him up.
		b.Customer <- c
		fmt.Printf("[CUSTOMER] #%d wakes up the barber\n", c.Number)
	default:
		// The barber is not sleeping - go to the waiting room.
		select {
		case b.WaitingRoom <- c:
			// The is a place in the waiting room, sit on it.
			fmt.Printf("[CUSTOMER] #%d sits in the waiting room\n", c.Number)
		default:
			// The is no place in the waiting room, leaving.
			fmt.Printf("[CUSTOMER] #%d leaves the shop\n", c.Number)
		}
	}
}

func main() {
	b := NewBarber(5)

	for i := 0; i < 20; i++ {
		c := NewCustomer(i)
		time.Sleep(time.Duration(rand.Intn(500)) * time.Millisecond)
		go c.WalkIn(b)
	}

	time.Sleep(2 * time.Second)
}