func (r *Runner) Signal(s os.Signal) error {
	r.childLock.RLock()
	defer r.childLock.RUnlock()
	if r.child == nil {
		return nil
	}
	return r.child.Signal(s)
}
func (r *Runner) Signal(s os.Signal) error {
	r.childLock.RLock()
	defer r.childLock.RUnlock()
	if r.child == nil {
		return nil
	}
	return r.child.Signal(s)
}
// Signal sends a signal to the child process, if it exists. Any errors that
// occur are returned.