Goで書くサンタクロース問題 http://karetta.jp/article/blog/oneline/030756

santa.go

// サンタクロース問題
// http://karetta.jp/article/blog/oneline/030756
package main

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

type visitor interface {
	act(home chan visitor)
}

type elf struct {
	id int
	r  *rand.Rand
}

type reindeer struct {
	id int
	r  *rand.Rand
}

func (d elf) act(home chan visitor) {
	time.Sleep(time.Duration(d.r.Int63n(10)) * time.Second)
	fmt.Printf("Elf #%d came to Santa's home\n", d.id)
	home <- d
}

func (c reindeer) act(home chan visitor) {
	time.Sleep(time.Duration(c.r.Int63n(8)) * time.Second)
	fmt.Printf("Reindeer #%d came to Santa's home\n", c.id)
	home <- c
}

func startReindeers(home chan visitor) {
	for i := 0; i < 9; i++ {
		c := reindeer{i, rand.New(rand.NewSource(time.Now().UnixNano() + int64(i)))}
		go c.act(home)
	}
}
func startElves(home chan visitor) {
	for i := 0; i < 10; i++ {
		d := elf{i, rand.New(rand.NewSource(time.Now().UnixNano() + int64(i)))}
		go d.act(home)
	}
}

func release(all []visitor, home chan visitor) []visitor {
	for _, member := range all {
		go member.act(home)
	}
	return queue()
}

func queue() []visitor {
	return make([]visitor, 0, 10)
}

func main() {
	home := make(chan visitor)

	startReindeers(home)
	startElves(home)

	reindeers := queue()
	elves := queue()

	stop := make(chan bool)
	go func() {
		time.Sleep(30 * time.Second)
		fmt.Println("STOP CALLED")
		stop <- true
	}()

	for {
		select {
		case <-stop:
			fmt.Println("Finished.")
			return
		case visitor := <-home:
			_, ok := visitor.(reindeer)

			if ok {
				reindeers = append(reindeers, visitor)
			} else {
				elves = append(elves, visitor)
			}
			if len(reindeers) == 9 {
				fmt.Println("*** Santa went to deliver presents: ", reindeers)
				time.Sleep(time.Duration(10) * time.Second)
				reindeers = release(reindeers, home)
				fmt.Println("*** Delivery finished")
			}
			if len(elves) == 3 {
				fmt.Println("### Santa is meeting up with elves: ", elves)
				time.Sleep(time.Duration(5) * time.Second)
				elves = release(elves, home)
				fmt.Println("### Meeting finished")
			}
		}
	}
}