letitfail.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"time"
)

const numWorkers = 3

var (
	workers  chan bool
	requests chan string
)

// worker executes requests.
func worker(id int) {
	for {
		switch r := <-requests; r {
		case "sleep":
			fmt.Println(id, "sleeping")
			time.Sleep(5 * time.Second)
		case "echo":
			fmt.Println(id, "echo")
		case "quit":
			os.Exit(0)
		default:
			panic(fmt.Sprintf("%v unkown command %q", id, r))
		}
	}
}

// run runs a function and catches any panic.
func run(f func(int), id int) {
	defer func() {
		if rec := recover(); rec != nil {
			fmt.Println("restarting failed worker: ", rec)
		}
		workers <- true
	}()
	f(id)
}

// monitor ensures that as numWorkers goroutines are running
// at any time.
func monitor() {
	workers = make(chan bool, numWorkers)
	for i := 0; i < cap(workers); i++ {
		workers <- true
	}

	id := 0
	for _ = range workers {
		id++
		go run(worker, id)
	}
}

// reader reads lines from stdin and puts them in the requests channel.
func reader() {
	requests = make(chan string)

	s := bufio.NewScanner(os.Stdin)
	for s.Scan() {
		requests <- s.Text()
	}
}

func main() {
	go monitor()
	reader()
}