Example of "errgroup" package

main.go

package main

import (
	"fmt"
	"net/http"
	"time"

	"golang.org/x/sync/errgroup"
)

type response struct {
	URL                  string
	StatusCode           int
	ElapsedTimeInSeconds float64
}

func main() {
	var (
		g    errgroup.Group
		urls = []string{
			"http://www.golang.org",
			"http://www.globoesporte.globo.com",
			"http://www.hackernews.com",
		}
	)

	// channel to communicate with goroutines
	output := make(chan response, len(urls))
	for _, url := range urls {
		url := url

		g.Go(func() error {
			// fetch the URL
			start := time.Now()
			resp, err := http.Get(url)

			if err != nil {
				return err
			}
			defer resp.Body.Close()

			output <- response{
				URL:                  url,
				StatusCode:           resp.StatusCode,
				ElapsedTimeInSeconds: time.Now().Sub(start).Seconds(),
			}
			return nil
		})
	}

	// create an anonymous function to handle with sync and close the given channel
	go func() {
		g.Wait()
		close(output)
	}()

	// this range will be printed as soon as we get data into output channel
	for o := range output {
		fmt.Printf("%s (%d): %.2f seconds\n",
			o.URL, o.StatusCode, o.ElapsedTimeInSeconds,
		)
	}

	// the output will be something like:
	//
	// http://www.globoesporte.globo.com (200): 2.09 seconds
	// http://www.hackernews.com (200): 2.10 seconds
	// http://www.golang.org (200): 2.56 seconds
}