code: 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)
  }
docs: // Signal sends a signal to the child process, if it exists. Any errors that
  // occur are returned.