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2023-06-26 17:30:52 +00:00
< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface-zh.html" > 译者序< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.< / strong > JSON< /
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2023-06-26 17:46:27 +00:00
< li > < em > 凹语言(专为 WebAssembly 设计): < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
< li > < em > KCL 配置语言(Rust): < a href = "https://github.com/kcl-lang/kcl" > https://github.com/kcl-lang/kcl< / a > < / em > < / li >
< / ul >
2023-03-31 10:23:29 +00:00
< hr >
< h2 id = "88-示例-并发的目录遍历" > < a class = "header" href = "#88-示例-并发的目录遍历" > 8.8. 示例: 并发的目录遍历< / a > < / h2 >
< p > 在本小节中， ， ， < / p >
< p > < u > < i > gopl.io/ch8/du1< / i > < / u > < / p >
< pre > < code class = "language-go" > // walkDir recursively walks the file tree rooted at dir
// and sends the size of each found file on fileSizes.
func walkDir(dir string, fileSizes chan< - int64) {
for _, entry := range dirents(dir) {
if entry.IsDir() {
subdir := filepath.Join(dir, entry.Name())
walkDir(subdir, fileSizes)
} else {
fileSizes < - entry.Size()
}
}
}
// dirents returns the entries of directory dir.
func dirents(dir string) []os.FileInfo {
entries, err := ioutil.ReadDir(dir)
if err != nil {
fmt.Fprintf(os.Stderr, " du1: %v\n" , err)
return nil
}
return entries
}
< / code > < / pre >
< p > ioutil.ReadDir函数会返回一个os.FileInfo类型的slice， ， ， < / p >
< p > 下面的主函数， ， < / p >
< pre > < code class = "language-go" > package main
import (
" flag"
" fmt"
" io/ioutil"
" os"
" path/filepath"
)
func main() {
// Determine the initial directories.
flag.Parse()
roots := flag.Args()
if len(roots) == 0 {
roots = []string{" ." }
}
// Traverse the file tree.
fileSizes := make(chan int64)
go func() {
for _, root := range roots {
walkDir(root, fileSizes)
}
close(fileSizes)
}()
// Print the results.
var nfiles, nbytes int64
for size := range fileSizes {
nfiles++
nbytes += size
}
printDiskUsage(nfiles, nbytes)
}
func printDiskUsage(nfiles, nbytes int64) {
fmt.Printf(" %d files %.1f GB\n" , nfiles, float64(nbytes)/1e9)
}
< / code > < / pre >
< p > 这个程序会在打印其结果之前卡住很长时间。< / p >
< pre > < code > $ go build gopl.io/ch8/du1
$ ./du1 $HOME /usr /bin /etc
213201 files 62.7 GB
< / code > < / pre >
< p > 如果在运行的时候能够让我们知道处理进度的话想必更好。但是， < / p >
< p > 下面这个du的变种会间歇打印内容， ， ， ， ， < / p >
< p > < u > < i > gopl.io/ch8/du2< / i > < / u > < / p >
< pre > < code class = "language-go" > var verbose = flag.Bool(" v" , false, " show verbose progress messages" )
func main() {
// ...start background goroutine...
// Print the results periodically.
var tick < -chan time.Time
if *verbose {
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
}
< / code > < / pre >
< p > 由于我们的程序不再使用range循环， ， ， ， ； ， < / p >
< p > 现在程序会悠闲地为我们打印更新流：< / p >
< pre > < code > $ go build gopl.io/ch8/du2
$ ./du2 -v $HOME /usr /bin /etc
28608 files 8.3 GB
54147 files 10.3 GB
93591 files 15.1 GB
127169 files 52.9 GB
175931 files 62.2 GB
213201 files 62.7 GB
< / code > < / pre >
< p > 然而这个程序还是会花上很长时间才会结束。完全可以并发调用walkDir， ， （ ） ， < / p >
< p > < u > < i > gopl.io/ch8/du3< / i > < / u > < / p >
< pre > < code class = "language-go" > func main() {
// ...determine roots...
// 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)
}()
// ...select loop...
}
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()
}
}
}
< / code > < / pre >
< p > 由于这个程序在高峰期会创建成百上千的goroutine， ， ， < / p >
< pre > < code class = "language-go" > // 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
// ...
< / code > < / pre >
< p > 这个版本比之前那个快了好几倍，尽管其具体效率还是和你的运行环境，机器配置相关。< / p >
< p > < strong > 练习 8.9： < / strong > 编写一个du工具， < / p >
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