I want to do redirection with RedirectResponse:

$response = new RedirectResponse($url);
$response->send();

and display the message after the redirection. But message isn't displayed. After little debugging I found that my initial (source) url loaded twice and drupal messages drupal_set_message are removing from $_SESSION in function drupal_get_messages. So I have not messages on my target $url.

Could somebody give me an advice?

Thanks in advance.

P.S. I'm doing it in hook_field_widget_form_alter.