Go语言圣经 - 习题 - 1.6. 并发获取多个URL

package main

import (
"fmt"
"io"
"io/ioutil"
"net/http"
"os"
"strings"
"time"
)

type results struct {
url    string
result string
}

func main() {

start := time.Now()
ch := make(chan string)
result := make(map[string]string)
for _, url := range os.Args[1:] {
if !strings.HasPrefix(url, "http://") {
url = "http://" + url
}
go fetch(url, ch)
go fetch(url, ch)
go fetch(url, ch)
}
for range os.Args[1:] {
for i := 0; i < 3; i++ {
fmt.Println(<-ch)
}
}

for k, v := range result {
fmt.Printf("%s : %s\n", k, v)
}
fmt.Printf("%.2fs elapsed\n", time.Since(start).Seconds())
}
func fetch(url string, ch chan<- string) {
start := time.Now()
resp, err := http.Get(url)
if err != nil {
ch <- fmt.Sprint(err)
return
}
nbytes, err := io.Copy(ioutil.Discard, resp.Body)
resp.Body.Close()
if err != nil {
ch <- fmt.Sprintf("while reading %s: %v", url, err)
return
}
secs := time.Since(start).Seconds()
ch <- fmt.Sprintf("%.2fs %7d %s", secs, nbytes, url)
}