import (
"flag"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"sync"
"time"
)
//一个已经被关闭的channel不会阻塞,已经被关闭的channel会实时返回
//goroutine退出,关闭done来进行广播
var done = make(chan struct{})
//判断done是否关闭,即是否执行goroutine退出
func cancelled() bool {
select {
case <-done:
return true
default:
return false
}
}
//获取目录dir下的文件大小
func walkDir(dir string, wg *sync.WaitGroup, fileSizes chan<- int64) {
defer wg.Done()
if cancelled() {
return
}
for _, entry := range dirents(dir) {
if entry.IsDir() { //目录
wg.Add(1)
subDir := filepath.Join(dir, entry.Name())
go walkDir(subDir, wg, fileSizes)
} else {
fileSizes <- entry.Size()
}
}
}
//sema is a counting semaphore for limiting concurrency in dirents
var sema = make(chan struct{}, 20)
//读取目录dir下的文件信息
func dirents(dir string) []os.FileInfo {
select {
case sema <- struct{}{}: //acquire token
case <-done:
return nil // cancelled
}
defer func() { <-sema }() //release token
entries, err := ioutil.ReadDir(dir)
if err != nil {
fmt.Fprintf(os.Stderr, "du: %vn", err)
return nil
}
return entries
}
//输出文件数量的大小
func printDiskUsage(nfiles, nbytes int64) {
fmt.Printf("%d files %.1f GBn", nfiles, float64(nbytes)/1e9)
}
//提供-v 参数会显示程序进度信息
var verbose = flag.Bool("v", false, "show verbose progress messages")
func Start() {
flag.Parse()
roots := flag.Args() //需要统计的目录
if len(roots) == 0 {
roots = []string{"."}
}
fileSizes := make(chan int64, 5)
var wg sync.WaitGroup
for _, root := range roots {
wg.Add(1)
go walkDir(root, &wg, fileSizes)
}
go func() {
os.Stdin.Read(make([]byte, 1)) //从标准输入读取一个字符,执行goroutine退出
close(done)
}()
go func() {
wg.Wait() //等待goroutine结束
close(fileSizes)
}()
var tick <-chan time.Time
if *verbose {
tick = time.Tick(100 * time.Millisecond) //输出时间间隔
}
var nfiles, nbytes int64
loop:
for {
select {
case <-done:
//to allow existing goroutines to finish
for range fileSizes { //fileSizes关闭时,for循环会自动结束
//Do nothing
}
return
case size, ok := <-fileSizes:
if !ok {
break loop
}
nfiles++
nbytes += size
case <-tick:
printDiskUsage(nfiles, nbytes)
}
}
printDiskUsage(nfiles, nbytes)
}
文章来源:智云一二三科技
文章标题:Golang 并发的退出
文章地址:https://www.zhihuclub.com/86943.shtml
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