I need to fetch multiple fields in parallel for my system from external services (in this example, simulated by Name(), Age() and CanDrive() methods).
The fetchUser() method does what I want, but it seems too verbose specially if you consider I could have 10+ fields. Are there better ways I can implement this?
playground: https://play.golang.org/p/90sNq1GmrD8
Code (same as in playground):
package main
import (
"fmt"
"sync"
)
type User struct {
Name string
Age int
CanDrive *bool
}
func Name() (string, error) {
return "foobar", nil
}
func Age() (int, error) {
return 25, nil
}
func CanDrive() (bool, error) {
return true, nil
}
func fetchUser() (*User, error) {
var wg sync.WaitGroup
errs := make(chan error)
user := &User{}
wg.Add(1)
go func() {
var err error
defer wg.Done()
user.Name, err = Name()
errs <- err
}()
wg.Add(1)
go func() {
var err error
defer wg.Done()
user.Age, err = Age()
errs <- err
}()
wg.Add(1)
go func() {
defer wg.Done()
canDrive, err := CanDrive()
if err == nil {
user.CanDrive = &canDrive
}
errs <- err
}()
// wait until all go-routines are completed successfully
// if that's the case, close the errs channel
go func() {
wg.Wait()
close(errs)
}()
// keep waiting for errors (or for the error channel to be closed
// if all calls succeed)
for err := range errs {
if err != nil {
return nil, err
}
}
return user, nil
}
func main() {
user, _ := fetchUser()
fmt.Println(user)
}
Without knowing more of the specifics of your scenario, my only suggestion would be to separate out the Go routine error handling into another package.
Fortunately, a package already exists that does the same thing, named errgroup. Below is an implementation of your original code using the errgroup package:
package main
import (
"context"
"fmt"
"golang.org/x/sync/errgroup"
)
type User struct {
Name string
Age int
CanDrive *bool
}
func Name() (string, error) {
return "foobar", nil
}
func Age() (int, error) {
return 25, nil
}
func CanDrive() (bool, error) {
return true, nil
}
func fetchUser(ctx context.Context) (*User, error) {
group, ctx := errgroup.WithContext(ctx)
user := &User{}
group.Go(func() (err error) {
user.Name, err = Name()
return
})
group.Go(func() (err error) {
user.Age, err = Age()
return
})
group.Go(func() error {
canDrive, err := CanDrive()
if err == nil {
user.CanDrive = &canDrive
}
return err
})
if err := group.Wait(); err != nil {
return nil, err
}
return user, nil
}
func main() {
user, err := fetchUser(context.Background())
fmt.Println(user, err)
}