Possible race condition

gistfile1.py

@transaction.atomic
def get_pending_messages():
    """Return a list of messages to be sent out and mark them as 'sent' in the db."""
    msg_qs = SMSSyncMessage.objects.select_for_update().filter(backend_name=self.name,
                                                               date_sent=None)

    messages = [dict(message=m.text, to=m.identity)
                for m in msg_qs]
    if msg_qs:
        msg_qs.update(date_sent=now())
    return messages