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//go:build unix
package dotlk
import (
"errors"
"io/fs"
"os"
"strconv"
"golang.org/x/sys/unix"
)
// TryLock returns nil if it acquired the lock,
// fs.ErrExist if another process has the lock.
func TryLock(name string) error {
for retry := true; retry; retry = false {
f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
if err == nil {
f.WriteString(strconv.Itoa(os.Getpid()))
f.Close()
return nil
}
if !errors.Is(err, fs.ErrExist) {
return err
}
if !removeStale(name) {
break
}
}
return fs.ErrExist
}
func removeStale(name string) bool {
buf, err := os.ReadFile(name)
if err != nil {
return errors.Is(err, fs.ErrNotExist)
}
pid, err := strconv.Atoi(string(buf))
if err != nil {
return false
}
if unix.Kill(pid, 0) == nil {
return false
}
err = os.Remove(name)
return err == nil || errors.Is(err, fs.ErrNotExist)
}
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