added url fetching example

concurrency/fetch_urls/main.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net/http"
+)
+
+func main() {
+	urls := []string{
+		"http://www.reddit.com/r/aww.json",
+		"http://www.reddit.com/r/funny.json",
+		"http://www.reddit.com/r/programming.json",
+	}
+
+	resc, errc := make(chan string), make(chan error)
+
+	for _, url := range urls {
+		go func(url string) {
+			body, err := fetch(url)
+			if err != nil {
+				errc <- err
+				return
+			}
+			resc <- string(body)
+		}(url)
+	}
+
+	for i := 0; i < len(urls); i++ {
+		select {
+		case res := <-resc:
+			fmt.Println(res)
+		case err := <-errc:
+			fmt.Println(err)
+		}
+	}
+}
+
+func fetch(url string) (string, error) {
+	res, err := http.Get(url)
+	if err != nil {
+		return "", err
+	}
+	body, err := ioutil.ReadAll(res.Body)
+	res.Body.Close()
+	if err != nil {
+		return "", err
+	}
+	return string(body), nil
+}