Reputation: 455
I'm facing a deadlock error in the following code, but I can't identify why. The goal of the code is to get the sha256 hash of all files in a given folder, recursively. (End goal is to remove duplicated files based on hash, as a learning project)
For that it spaws a goroutine that spawns another goroutine for each file to get the hash. The hash is stores in a channel and read at the end of the code in a simple loop.
Based on the prints, all files are checked, and the wg.Add and Done seem to be on the right place.
Code:
package main
import (
"crypto/sha256"
"fmt"
"io"
"io/fs"
"log"
"os"
"path/filepath"
"sync"
"time"
)
func get_fsha256sum(filepath string) string {
f, err := os.Open(filepath)
if err != nil {
log.Fatal(err)
}
defer f.Close()
return get_sha256sum(f)
}
func get_sha256sum(r io.Reader) string {
h := sha256.New()
if _, err := io.Copy(h, r); err != nil {
log.Fatal(err)
}
return fmt.Sprintf("%x", h.Sum(nil))
}
func main() {
start := time.Now()
ch := make(chan string, 10000)
var wg sync.WaitGroup
var get_fsha256sum_wrap = func(filepath string) {
start := time.Now()
ch <- get_fsha256sum(filepath)
fmt.Printf("%f-%s\n", filepath, time.Since(start))
wg.Done()
}
var walk_func = func(filepath string, info fs.DirEntry, err error) error {
wg.Add(1)
if err != nil {
return err
}
if info.IsDir() {
return nil
}
go get_fsha256sum_wrap(filepath)
return nil
}
var over_wrap = func(root string) {
filepath.WalkDir(root, walk_func)
wg.Wait()
close(ch)
}
go over_wrap("/run/media/user/Red/pictures_master/2021/01")
for v := range ch {
fmt.Println(v)
}
fmt.Printf("%s", time.Since(start))
}
Error Message:
fatal error: all goroutines are asleep - deadlock!
goroutine 1 [chan receive]:
main.main()
/home/user/go_phockup/main.go:66 +0x273
goroutine 18 [semacquire]:
sync.runtime_Semacquire(0xc0000b8018)
/usr/local/go/src/runtime/sema.go:56 +0x45
sync.(*WaitGroup).Wait(0xc0000b8010)
/usr/local/go/src/sync/waitgroup.go:130 +0x65
main.main.func3(0x4e3d3f, 0x2b)
/home/go_phockup/main.go:62 +0x5e
created by main.main
/home/user/go_phockup/main.go:65 +0x1bd
exit status 2
Any idea what's wrong?
Upvotes: 0
Views: 59
Reputation: 51632
Your waitgroup is waiting for more goroutines than you created. The walk_func adds to the wg
, but may return without creating a new goroutine. Replace with:
var walk_func = func(filepath string, info fs.DirEntry, err error) error{
if err != nil {
return err
}
if info.IsDir() {
return nil
}
wg.Add(1)
go get_fsha256sum_wrap(filepath)
return nil
}
Upvotes: 2