golang concurrency exercise

concurrency.go

// https://talks.golang.org/2012/concurrency.slide#36
package main

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

type Message struct {
	str  string
	wait chan bool
}

func boring(msg string) <-chan Message {
	c := make(chan Message)
	waitForIt := make(chan bool) // Shared between all messages.
	go func() {
		for i := 0; ; i++ {
			c <- Message{
				str:  fmt.Sprintf("%s: %d", msg, i),
				wait: waitForIt,
			}

			time.Sleep(time.Duration(rand.Intn(2e3)) * time.Millisecond)
			<-waitForIt
		}
	}()
	return c
}

func fanIn(input1, input2 <-chan Message) <-chan Message {
	c := make(chan Message)

	go func() {
		for {
			select {
			case i1 := <-input1:
				c <- i1
			case i2 := <-input2:
				c <- i2
			}
		}
	}()

	return c
}

func main() {
	timesLimit := 5

	c := fanIn(boring("Joe"), boring("Ann"))

	for i := 0; i < timesLimit; i++ {
		timeout := time.After(5 * time.Second)
		group := make([]Message, 0)

		for len(group) < 2 {
			select {
			case msg := <-c:
				fmt.Println(msg.str)
				group = append(group, msg)
			case <-timeout:
				fmt.Printf("No. %d: You talk too much.\n", i)
				return
			}
		}

		for _, msg := range group {
			msg.wait <- true
		}

	}
	fmt.Println("You're boring; I'm leaving.")
}