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