The coupons RPC server

server.go

package main

import (
	"fmt"
	"log"
	"net"
	"net/http"
	"net/rpc"
)

type Args struct {
	Id int
}

type Competition struct {
	Coupons chan int
}

type Server struct {
	competitions map[int]*Competition
}

var max int = 1000

var done chan bool

func (s *Server) Compute(args *Args, reply *string) error {
	c := s.competitions[args.Id]

	if len(c.Coupons) == 0 {
		*reply = "error"
		return nil
	}

	n := <-c.Coupons

	total := args.Id*max + (n - 1)
	*reply = fmt.Sprintf("%x", total)
	return nil
}

func main() {
	startServer()
	startClient()
}

func startServer() {
	server := new(Server)

	server.competitions = make(map[int]*Competition, 10)

	for i := 0; i < 10; i++ {
		competition := new(Competition)

		competition.Coupons = make(chan int, max)

		for j := 0; j < max; j++ {
			competition.Coupons <- j + 1
		}

		server.competitions[i+1] = competition
	}

	rpc.Register(server)
	rpc.HandleHTTP()
	l, e := net.Listen("tcp", ":1234")
	if e != nil {
		log.Fatal("listen error:", e)
	}

	go http.Serve(l, nil)
}

func startClient() {
	done = make(chan bool)

	client, err := rpc.DialHTTP("tcp", "localhost"+":1234")
	if err != nil {
		log.Fatal("dialing:", err)
	}

	fmt.Println("**Coupons for server 4**")

	args := &Args{4}

	for i := 0; i < max; i++ {
		go func() {
			var reply string
			err = client.Call("Server.Compute", args, &reply)
			if err != nil {
				log.Fatal("compute error:", err)
			}
			fmt.Println("Response:", reply)
			done <- true
		}()
	}

	for i := 0; i < 1000; i++ {
		<-done
	}
}