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102 lines
2.4 KiB
Go
102 lines
2.4 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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"crypto/md5"
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"fmt"
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"io/ioutil"
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"log"
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"os"
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"path/filepath"
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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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// Pipeline demonstrates the use of a Group to implement a multi-stage
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// pipeline: a version of the MD5All function with bounded parallelism from
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// https://blog.golang.org/pipelines.
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func ExampleGroup_pipeline() {
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m, err := MD5All(context.Background(), ".")
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if err != nil {
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log.Fatal(err)
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}
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for k, sum := range m {
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fmt.Printf("%s:\t%x\n", k, sum)
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}
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}
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type result struct {
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path string
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sum [md5.Size]byte
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}
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// MD5All reads all the files in the file tree rooted at root and returns a map
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// from file path to the MD5 sum of the file's contents. If the directory walk
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// fails or any read operation fails, MD5All returns an error.
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func MD5All(ctx context.Context, root string) (map[string][md5.Size]byte, error) {
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// ctx is canceled when g.Wait() returns. When this version of MD5All returns
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// - even in case of error! - we know that all of the goroutines have finished
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// and the memory they were using can be garbage-collected.
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g, ctx := errgroup.WithContext(ctx)
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paths := make(chan string)
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g.Go(func() error {
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defer close(paths)
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return filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
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if err != nil {
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return err
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}
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if !info.Mode().IsRegular() {
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return nil
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}
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select {
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case paths <- path:
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case <-ctx.Done():
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return ctx.Err()
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}
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return nil
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})
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})
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// Start a fixed number of goroutines to read and digest files.
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c := make(chan result)
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const numDigesters = 20
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for i := 0; i < numDigesters; i++ {
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g.Go(func() error {
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for path := range paths {
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data, err := ioutil.ReadFile(path)
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if err != nil {
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return err
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}
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select {
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case c <- result{path, md5.Sum(data)}:
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case <-ctx.Done():
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return ctx.Err()
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}
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}
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return nil
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})
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}
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go func() {
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g.Wait()
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close(c)
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}()
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m := make(map[string][md5.Size]byte)
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for r := range c {
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m[r.path] = r.sum
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}
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// Check whether any of the goroutines failed. Since g is accumulating the
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// errors, we don't need to send them (or check for them) in the individual
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// results sent on the channel.
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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 m, nil
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}
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