parallel

main.go

// http://play.golang.org/p/cwMSE2imEN
package main

import (
	"errors"
	"fmt"
	"sync"
)

func main() {
	err := do()
	fmt.Println(err)
}

var Areas = []string{"a", "b", "c", "d", "e", "f"}

type request struct {
	area string
}

type result struct {
	err error
}

func do() error {
	req := make(chan request)
	stop := make(chan struct{})

	res := parallel(func(area string) error {
		fmt.Println(area)
		if area == "e" {
			return errors.New("error")
		}
		return nil
	}, req, stop, 3)

	go func() {
		for _, area := range Areas {
			req <- request{area}
		}
	}()

	for range Areas {
		r := <-res
		if r.err != nil {
			close(stop)
			return r.err
		}
	}
	close(stop)
	return nil
}

func parallel(fn func(area string) error, req chan request, stop chan struct{}, concurrency int) chan result {
	res := make(chan result)
	var wg sync.WaitGroup
	wg.Add(concurrency)

	for c := 0; c < concurrency; c++ {
		go func() {
			for {
				select {
				case re := <-req:
					err := fn(re.area)
					res <- result{err: err}
				case <-stop:
					break
				}
			}
			wg.Done()
		}()
	}

	go func() {
		wg.Wait()
		close(res)
	}()

	return res
}