Golang Goroutine Error "all goroutines are asleep - deadlock!"

Question

I am trying to make a code to scan from a folder link all my files and make a "top 10" by his size with also a regexp based on his content and his name. file. By it content, I make channels with goroutines but I dont understand why each time my goroutines are locked. Here is my code:

package main

import (
    "flag"
    "fmt"
    "io/ioutil"
    "regexp"
    "runtime"
    "sort"
    "sync"
    "time"
)

var rName = ".php"
var rContent = "php"
var maxSize, minSize int64
var files_ten []File

func main() {
    start := time.Now()

    channelOne := make(chan File)
    channelTwo := make(chan File)

    var wg sync.WaitGroup
    var path string
    flag.StringVar(&path, "path", "", "Path to folder")
    flag.Parse()
    fmt.Println("Path=", path)

    for i := 0; i < runtime.NumCPU(); i++ {
        go check(channelOne, channelTwo, &wg)
    }

    go top10(channelTwo, &wg)

    wg.Wait()

    getFolder(path, channelOne, &wg)

    fmt.Println("top 10", files_ten)
    t := time.Now()
    current := t.Sub(start)
    fmt.Println(current)

}

type File struct {
    Size int64
    Name string
    Path string
}

func (this File) GetSize() int64 {
    return this.Size
}

func getFolder(path string, channelOne chan File, wg *sync.WaitGroup) {
    folder, err := ioutil.ReadDir(path)

    if err != nil {
        fmt.Println("Error:", err)
        return
    }

    for _, data := range folder {
        if data.IsDir() {
            var newFolder string = path + data.Name() + "/"
            getFolder(newFolder, channelOne, wg)
        } else {
            wg.Add(1)
            channelOne <- File{Size: data.Size(), Name: data.Name(), Path: path}
        }
    }
}

func check(channelOne chan File, channelTwo chan File, wg *sync.WaitGroup) {
    for {
        file := <-channelOne
        rName := regexp.MustCompile(rName)

        maxSize = 10000
        minSize = 0

        if rName.MatchString(file.Name) {
            if file.Size <= maxSize && file.Size >= minSize {
                f, err := ioutil.ReadFile(file.Path + "/" + file.Name)

                if err != nil {
                    fmt.Println("Error:", err)
                    return
                }
                rContent := regexp.MustCompile(rContent)
                if rContent.MatchString(string(f)) {
                    channelTwo <- file
                } else {
                    wg.Done()
                }
            } else {
                wg.Done()
            }
        } else {
            wg.Done()
        }
    }
}

func sortFilesFromBiggestToLowerSize(arrayFile []File) []File {
    sort.Slice(arrayFile, func(i, j int) bool {
        return arrayFile[i].Size > arrayFile[j].Size
    })
    return arrayFile
}

func top10(channelTwo chan File, wg *sync.WaitGroup) []File {
    for {
        f := <-channelTwo

        if len(files_ten) == 10 {
            if f.Size > files_ten[0].Size || f.Size >
                files_ten[len(files_ten)-1].Size {
                files_ten = files_ten[:len(files_ten)-1]
                files_ten = append(files_ten, f)
                return sortFilesFromBiggestToLowerSize(files_ten)
            }
        } else {
            sortFilesFromBiggestToLowerSize(files_ten)
            return append(files_ten, f)
        }
        wg.Done()
        return files_ten
    }
}

Here is the error each time I compile it :

go run filebysize.go --path=C:/wamp64/www/symfony/init/cours1/
Path= C:/wamp64/www/symfony/init/cours1/
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan send]:
main.getFolder(0xc04210a3c0, 0x3d, 0xc04204c0c0, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:72 +0x28a
main.getFolder(0xc04210a200, 0x32, 0xc04204c0c0, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:69 +0x151
main.getFolder(0xc04200e6c0, 0x26, 0xc04204c0c0, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:69 +0x151
main.getFolder(0xc042051f57, 0x22, 0xc04204c0c0, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:69 +0x151
main.main()
    C:/Users/Sahra/Documents/go/display/filebysize.go:37 +0x2e0

goroutine 19 [chan send]:
main.check(0xc04204c0c0, 0xc04204c120, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:95 +0x2ec
created by main.main
    C:/Users/Sahra/Documents/go/display/filebysize.go:32 +0x26d

goroutine 20 [chan send]:
main.check(0xc04204c0c0, 0xc04204c120, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:95 +0x2ec
created by main.main
    C:/Users/Sahra/Documents/go/display/filebysize.go:32 +0x26d

goroutine 21 [chan send]:
main.check(0xc04204c0c0, 0xc04204c120, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:95 +0x2ec
created by main.main
    C:/Users/Sahra/Documents/go/display/filebysize.go:32 +0x26d

goroutine 22 [chan send]:
main.check(0xc04204c0c0, 0xc04204c120, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:95 +0x2ec
created by main.main
    C:/Users/Sahra/Documents/go/display/filebysize.go:32 +0x26d

goroutine 23 [chan send]:
main.check(0xc04204c0c0, 0xc04204c120, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:95 +0x2ec
created by main.main
    C:/Users/Sahra/Documents/go/display/filebysize.go:32 +0x26d

goroutine 24 [chan send]:
main.check(0xc04204c0c0, 0xc04204c120, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:95 +0x2ec
created by main.main
    C:/Users/Sahra/Documents/go/display/filebysize.go:32 +0x26d

goroutine 25 [chan send]:
main.check(0xc04204c0c0, 0xc04204c120, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:95 +0x2ec
created by main.main
    C:/Users/Sahra/Documents/go/display/filebysize.go:32 +0x26d

goroutine 26 [chan send]:
main.check(0xc04204c0c0, 0xc04204c120, 0xc04204e210)
    C:/Users/Sahra/Documents/go/display/filebysize.go:95 +0x2ec
created by main.main
    C:/Users/Sahra/Documents/go/display/filebysize.go:32 +0x26d
exit status 2

This is a lot of code to understand, but some things look off: the return value from top10 is ignored, it looks like waitgroup is used to count something other than executing goroutines. — Cerise Limón
You are right, the problem was that in the function top 10, i dont need to return anything, include at the if else statement, thanks a lot !!!!!!!!!!!!!!!!!!!! — akali leona

Adrian Adrian · Accepted Answer · 2017-12-14T16:47:12

You're trying to send on channelOne, but nothing reads from it until after wg.Done, hence the deadlock: the routines trying to send to it must wait until something is available to receive, which never occurs.

Also, your WaitGroup use is off; you should call Add before starting each goroutine you want to wait on, then call Done at the end of the goroutine. A single goroutine should not call Add or Done in a loop, and a goroutine should not call Done if there is no associated Add call.

It looks like you have multiple for loops that will never exit; they have no conditions and no breaks.

You can also loop over channels much more simply. You can replace constructs like:

for {
    file := <-channelOne

with the simpler:

for file := range channelOne {

This has the added advantage that when the channel you're ranging over is closed, the loop will exit, allowing you to use closing the channel as a signal that consumers can stop.

Golang Goroutine Error "all goroutines are asleep - deadlock!"

1 Answers