code: func funlock(db *DB) error {
  	err := unlockFileEx(syscall.Handle(db.lockfile.Fd()), 0, 1, 0, &syscall.Overlapped{})
  	db.lockfile.Close()
  	os.Remove(db.path + lockExt)
  	return err
  }
docs: // funlock releases an advisory lock on a file descriptor.