'This is the same as NotifyQueue but for several session_ids at once.
Args:
notifications: A list of notifications.
mutation_pool: A MutationPool object to schedule Notifications on.
Raises:
RuntimeError: An invalid session_id was passed.'

def MultiNotifyQueue(self, notifications, mutation_pool=None):

    extract_queue = (lambda notification: notification.session_id.Queue())
    for (queue, notifications) in utils.GroupBy(notifications, extract_queue).iteritems():
        self._MultiNotifyQueue(queue, notifications, mutation_pool=mutation_pool)
