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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package errgroup_test
import (
"context"
"errors"
"fmt"
"net/http"
"os"
"testing"
"golang.org/x/sync/errgroup"
)
var (
Web = fakeSearch("web")
Image = fakeSearch("image")
Video = fakeSearch("video")
)
type Result string
type Search func(ctx context.Context, query string) (Result, error)
func fakeSearch(kind string) Search {
return func(_ context.Context, query string) (Result, error) {
return Result(fmt.Sprintf("%s result for %q", kind, query)), nil
}
}
// JustErrors illustrates the use of a Group in place of a sync.WaitGroup to
// simplify goroutine counting and error handling. This example is derived from
// the sync.WaitGroup example at https://golang.org/pkg/sync/#example_WaitGroup.
func ExampleGroup_justErrors() {
g := new(errgroup.Group)
var urls = []string{
"http://www.golang.org/",
"http://www.google.com/",
"http://www.somestupidname.com/",
}
for _, url := range urls {
// Launch a goroutine to fetch the URL.
url := url // https://golang.org/doc/faq#closures_and_goroutines
g.Go(func() error {
// Fetch the URL.
resp, err := http.Get(url)
if err == nil {
resp.Body.Close()
}
return err
})
}
// Wait for all HTTP fetches to complete.
if err := g.Wait(); err == nil {
fmt.Println("Successfully fetched all URLs.")
}
}
// Parallel illustrates the use of a Group for synchronizing a simple parallel
// task: the "Google Search 2.0" function from
// https://talks.golang.org/2012/concurrency.slide#46, augmented with a Context
// and error-handling.
func ExampleGroup_parallel() {
Google := func(ctx context.Context, query string) ([]Result, error) {
g, ctx := errgroup.WithContext(ctx)
searches := []Search{Web, Image, Video}
results := make([]Result, len(searches))
for i, search := range searches {
i, search := i, search // https://golang.org/doc/faq#closures_and_goroutines
g.Go(func() error {
result, err := search(ctx, query)
if err == nil {
results[i] = result
}
return err
})
}
if err := g.Wait(); err != nil {
return nil, err
}
return results, nil
}
results, err := Google(context.Background(), "golang")
if err != nil {
fmt.Fprintln(os.Stderr, err)
return
}
for _, result := range results {
fmt.Println(result)
}
// Output:
// web result for "golang"
// image result for "golang"
// video result for "golang"
}
func TestZeroGroup(t *testing.T) {
err1 := errors.New("errgroup_test: 1")
err2 := errors.New("errgroup_test: 2")
cases := []struct {
errs []error
}{
{errs: []error{}},
{errs: []error{nil}},
{errs: []error{err1}},
{errs: []error{err1, nil}},
{errs: []error{err1, nil, err2}},
}
for _, tc := range cases {
g := new(errgroup.Group)
var firstErr error
for i, err := range tc.errs {
err := err
g.Go(func() error { return err })
if firstErr == nil && err != nil {
firstErr = err
}
if gErr := g.Wait(); gErr != firstErr {
t.Errorf("after %T.Go(func() error { return err }) for err in %v\n"+
"g.Wait() = %v; want %v",
g, tc.errs[:i+1], err, firstErr)
}
}
}
}
func TestWithContext(t *testing.T) {
errDoom := errors.New("group_test: doomed")
cases := []struct {
errs []error
want error
}{
{want: nil},
{errs: []error{nil}, want: nil},
{errs: []error{errDoom}, want: errDoom},
{errs: []error{errDoom, nil}, want: errDoom},
}
for _, tc := range cases {
g, ctx := errgroup.WithContext(context.Background())
for _, err := range tc.errs {
err := err
g.Go(func() error { return err })
}
if err := g.Wait(); err != tc.want {
t.Errorf("after %T.Go(func() error { return err }) for err in %v\n"+
"g.Wait() = %v; want %v",
g, tc.errs, err, tc.want)
}
canceled := false
select {
case <-ctx.Done():
canceled = true
default:
}
if !canceled {
t.Errorf("after %T.Go(func() error { return err }) for err in %v\n"+
"ctx.Done() was not closed",
g, tc.errs)
}
}
}
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