149 lines
2.8 KiB
Go
149 lines
2.8 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// This file is just a place to put example code from the book.
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// It does not actually run any code in gopl.io/ch8/thumbnail.
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package thumbnail_test
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import (
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"log"
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"os"
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"sync"
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"gopl.io/ch8/thumbnail"
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)
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//!+1
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// makeThumbnails makes thumbnails of the specified files.
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func makeThumbnails(filenames []string) {
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for _, f := range filenames {
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if _, err := thumbnail.ImageFile(f); err != nil {
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log.Println(err)
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}
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}
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}
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//!-1
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//!+2
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// NOTE: incorrect!
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func makeThumbnails2(filenames []string) {
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for _, f := range filenames {
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go thumbnail.ImageFile(f) // NOTE: ignoring errors
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}
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}
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//!-2
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//!+3
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// makeThumbnails3 makes thumbnails of the specified files in parallel.
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func makeThumbnails3(filenames []string) {
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ch := make(chan struct{})
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for _, f := range filenames {
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go func(f string) {
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thumbnail.ImageFile(f) // NOTE: ignoring errors
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ch <- struct{}{}
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}(f)
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}
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// Wait for goroutines to complete.
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for range filenames {
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<-ch
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}
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}
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//!-3
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//!+4
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// makeThumbnails4 makes thumbnails for the specified files in parallel.
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// It returns an error if any step failed.
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func makeThumbnails4(filenames []string) error {
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errors := make(chan error)
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for _, f := range filenames {
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go func(f string) {
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_, err := thumbnail.ImageFile(f)
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errors <- err
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}(f)
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}
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for range filenames {
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if err := <-errors; err != nil {
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return err // NOTE: incorrect: goroutine leak!
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}
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}
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return nil
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}
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//!-4
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//!+5
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// makeThumbnails5 makes thumbnails for the specified files in parallel.
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// It returns the generated file names in an arbitrary order,
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// or an error if any step failed.
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func makeThumbnails5(filenames []string) (thumbfiles []string, err error) {
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type item struct {
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thumbfile string
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err error
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}
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ch := make(chan item, len(filenames))
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for _, f := range filenames {
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go func(f string) {
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var it item
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it.thumbfile, it.err = thumbnail.ImageFile(f)
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ch <- it
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}(f)
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}
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for range filenames {
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it := <-ch
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if it.err != nil {
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return nil, it.err
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}
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thumbfiles = append(thumbfiles, it.thumbfile)
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}
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return thumbfiles, nil
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}
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//!-5
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//!+6
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// makeThumbnails6 makes thumbnails for each file received from the channel.
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// It returns the number of bytes occupied by the files it creates.
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func makeThumbnails6(filenames <-chan string) int64 {
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sizes := make(chan int64)
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var wg sync.WaitGroup // number of working goroutines
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for f := range filenames {
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wg.Add(1)
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// worker
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go func(f string) {
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defer wg.Done()
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thumb, err := thumbnail.ImageFile(f)
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if err != nil {
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log.Println(err)
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return
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}
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info, _ := os.Stat(thumb) // OK to ignore error
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sizes <- info.Size()
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}(f)
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}
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// closer
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go func() {
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wg.Wait()
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close(sizes)
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}()
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var total int64
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for size := range sizes {
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total += size
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}
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return total
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}
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//!-6
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