gopl-zh.github.com/vendor/gopl.io/ch8/du3/main.go

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2015-12-09 07:57:17 +00:00
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 250.
// The du3 command computes the disk usage of the files in a directory.
package main
// The du3 variant traverses all directories in parallel.
// It uses a concurrency-limiting counting semaphore
// to avoid opening too many files at once.
import (
"flag"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"sync"
"time"
)
var vFlag = flag.Bool("v", false, "show verbose progress messages")
//!+
func main() {
// ...determine roots...
//!-
flag.Parse()
// Determine the initial directories.
roots := flag.Args()
if len(roots) == 0 {
roots = []string{"."}
}
//!+
// Traverse each root of the file tree in parallel.
fileSizes := make(chan int64)
var n sync.WaitGroup
for _, root := range roots {
n.Add(1)
go walkDir(root, &n, fileSizes)
}
go func() {
n.Wait()
close(fileSizes)
}()
//!-
// Print the results periodically.
var tick <-chan time.Time
if *vFlag {
tick = time.Tick(500 * time.Millisecond)
}
var nfiles, nbytes int64
loop:
for {
select {
case size, ok := <-fileSizes:
if !ok {
break loop // fileSizes was closed
}
nfiles++
nbytes += size
case <-tick:
printDiskUsage(nfiles, nbytes)
}
}
printDiskUsage(nfiles, nbytes) // final totals
//!+
// ...select loop...
}
//!-
func printDiskUsage(nfiles, nbytes int64) {
fmt.Printf("%d files %.1f GB\n", nfiles, float64(nbytes)/1e9)
}
// walkDir recursively walks the file tree rooted at dir
// and sends the size of each found file on fileSizes.
//!+walkDir
func walkDir(dir string, n *sync.WaitGroup, fileSizes chan<- int64) {
defer n.Done()
for _, entry := range dirents(dir) {
if entry.IsDir() {
n.Add(1)
subdir := filepath.Join(dir, entry.Name())
go walkDir(subdir, n, fileSizes)
} else {
fileSizes <- entry.Size()
}
}
}
//!-walkDir
//!+sema
// sema is a counting semaphore for limiting concurrency in dirents.
var sema = make(chan struct{}, 20)
// dirents returns the entries of directory dir.
func dirents(dir string) []os.FileInfo {
sema <- struct{}{} // acquire token
defer func() { <-sema }() // release token
// ...
//!-sema
entries, err := ioutil.ReadDir(dir)
if err != nil {
fmt.Fprintf(os.Stderr, "du: %v\n", err)
return nil
}
return entries
}