concgroup provides almost the same features to goroutine groups as golang.org/x/sync/errgroup but ensures sequential run of goroutines with the same group key.
package main
import (
"fmt"
"net/http"
"time"
"github.com/k1LoW/concgroup"
)
func main() {
cg := new(concgroup.Group)
var urlgroups = map[string][]string{
"go": {
"https://go.dev/",
"https://go.dev/dl/",
},
"google": {
"http://www.google.com/",
},
}
for key, ug := range urlgroups {
key := key
for _, url := range ug {
url := url // https://golang.org/doc/faq#closures_and_goroutines
cg.Go(key, func() error {
// Fetch URL sequentially by key
resp, err := http.Get(url)
if err == nil {
resp.Body.Close()
}
return err
})
}
}
// Wait for all HTTP fetches to complete.
if err := cg.Wait(); err == nil {
fmt.Println("Successfully fetched all URLs.")
}
}