Created
May 25, 2017 16:15
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Coffee shop concurrency. Examining concurrency in the real world by scaling a coffee shop's efficiency.
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| package main | |
| import ( | |
| "fmt" | |
| "github.com/icrowley/fake" | |
| "math/rand" | |
| "time" | |
| ) | |
| const ( | |
| averageTimeToNextCustomer = 3 | |
| averageWaitingTime = 3 | |
| ) | |
| var ( | |
| acceptedOrders int = 0 | |
| missedOrders int = 0 | |
| ) | |
| type Brewable interface { | |
| Brew() | |
| String() string | |
| } | |
| type Americano struct{} | |
| type Cappuccino struct{} | |
| type Latte struct{} | |
| type Customer struct { | |
| Name string | |
| } | |
| type Order struct { | |
| Number int | |
| Type Brewable | |
| Customer *Customer | |
| } | |
| func (c *Americano) Brew() { | |
| fmt.Println("Brewing an", c.String()) | |
| time.Sleep(time.Second * 5) | |
| } | |
| func (c *Americano) String() string { | |
| return "Americano" | |
| } | |
| func (c *Cappuccino) Brew() { | |
| fmt.Println("Brewing a", c.String()) | |
| time.Sleep(time.Second * time.Duration(rand.Intn(7)+7)) | |
| } | |
| func (c *Cappuccino) String() string { | |
| return "Cappuccino" | |
| } | |
| func (c *Latte) Brew() { | |
| fmt.Println("Brewing a", c.String()) | |
| time.Sleep(time.Second * time.Duration(rand.Intn(10)+10)) | |
| } | |
| func (c Latte) String() string { | |
| return "Latte" | |
| } | |
| func init() { | |
| rand.Seed(time.Now().UTC().UnixNano()) | |
| } | |
| func generateOrders(orderQueue chan<- *Order) { | |
| // Menu | |
| coffees := []Brewable{&Americano{}, &Cappuccino{}, &Latte{}} | |
| customerNumber := 0 | |
| for { | |
| customerName := fake.FirstName() | |
| fmt.Printf("[%d] %s entered the shop.\n", customerNumber, customerName) | |
| order := &Order{ | |
| Number: customerNumber, | |
| Type: coffees[rand.Intn(len(coffees))], | |
| Customer: &Customer{Name: customerName}, | |
| } | |
| customerNumber += 1 | |
| select { | |
| case orderQueue <- order: | |
| acceptedOrders += 1 | |
| fmt.Printf("[%d] %s ordered %s.\n", order.Number, customerName, order.Type.String()) | |
| case <-time.After(time.Second * time.Duration(averageWaitingTime)): | |
| missedOrders += 1 | |
| fmt.Printf("[%d] %s got impatient waiting to order %s, and left.\n", order.Number, customerName, order.Type.String()) | |
| } | |
| time.Sleep(time.Second * time.Duration(rand.Intn(averageTimeToNextCustomer))) | |
| } | |
| } | |
| func handleOrders(orderQueue <-chan *Order, baristaName string) { | |
| for order := range orderQueue { | |
| order.Type.Brew() | |
| fmt.Printf("[%d] %s brewed %s for %s\n", order.Number, baristaName, order.Type.String(), order.Customer.Name) | |
| } | |
| } | |
| func main() { | |
| defer func() { | |
| fmt.Println("Accepted orders:", acceptedOrders) | |
| fmt.Println("Missed orders:", missedOrders) | |
| }() | |
| // Order queue | |
| orderQueue := make(chan *Order, 5) | |
| // Cashiers | |
| go generateOrders(orderQueue) | |
| // Baristas | |
| go handleOrders(orderQueue, "Ian") | |
| go handleOrders(orderQueue, "Harry") | |
| go handleOrders(orderQueue, "Roey") | |
| // Close the coffee shop | |
| time.Sleep(30 * time.Second) | |
| } |
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