public function getExpired($timeout)
    {
        $expired = array();
        $timeoutAt = microtime(true) - ($timeout / 1000);
        foreach ($this->clients as $client) {
            if ($client->getTime() > $timeoutAt) {
                // Clients are ordered by time.
                break;
            }
            $expired[] = $client;
        }

        return $expired;
    }