119 lines
2.3 KiB
Go
119 lines
2.3 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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// See page 250.
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// The du3 command computes the disk usage of the files in a directory.
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package main
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// The du3 variant traverses all directories in parallel.
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// It uses a concurrency-limiting counting semaphore
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// to avoid opening too many files at once.
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import (
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"flag"
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"fmt"
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"io/ioutil"
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"os"
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"path/filepath"
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"sync"
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"time"
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)
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var vFlag = flag.Bool("v", false, "show verbose progress messages")
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//!+
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func main() {
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// ...determine roots...
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//!-
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flag.Parse()
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// Determine the initial directories.
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roots := flag.Args()
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if len(roots) == 0 {
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roots = []string{"."}
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}
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//!+
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// Traverse each root of the file tree in parallel.
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fileSizes := make(chan int64)
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var n sync.WaitGroup
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for _, root := range roots {
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n.Add(1)
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go walkDir(root, &n, fileSizes)
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}
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go func() {
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n.Wait()
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close(fileSizes)
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}()
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//!-
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// Print the results periodically.
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var tick <-chan time.Time
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if *vFlag {
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tick = time.Tick(500 * time.Millisecond)
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}
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var nfiles, nbytes int64
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loop:
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for {
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select {
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case size, ok := <-fileSizes:
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if !ok {
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break loop // fileSizes was closed
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}
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nfiles++
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nbytes += size
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case <-tick:
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printDiskUsage(nfiles, nbytes)
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}
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}
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printDiskUsage(nfiles, nbytes) // final totals
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//!+
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// ...select loop...
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}
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//!-
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func printDiskUsage(nfiles, nbytes int64) {
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fmt.Printf("%d files %.1f GB\n", nfiles, float64(nbytes)/1e9)
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}
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// walkDir recursively walks the file tree rooted at dir
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// and sends the size of each found file on fileSizes.
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//!+walkDir
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func walkDir(dir string, n *sync.WaitGroup, fileSizes chan<- int64) {
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defer n.Done()
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for _, entry := range dirents(dir) {
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if entry.IsDir() {
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n.Add(1)
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subdir := filepath.Join(dir, entry.Name())
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go walkDir(subdir, n, fileSizes)
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} else {
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fileSizes <- entry.Size()
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}
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}
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}
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//!-walkDir
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//!+sema
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// sema is a counting semaphore for limiting concurrency in dirents.
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var sema = make(chan struct{}, 20)
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// dirents returns the entries of directory dir.
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func dirents(dir string) []os.FileInfo {
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sema <- struct{}{} // acquire token
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defer func() { <-sema }() // release token
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// ...
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//!-sema
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entries, err := ioutil.ReadDir(dir)
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if err != nil {
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fmt.Fprintf(os.Stderr, "du: %v\n", err)
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return nil
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}
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return entries
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}
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