php-rdkafka: a strange issue on rdkafka,can not exit from the script

• PHP version: 5.6.21
• librdkafka version: 0.9.1
• php-rdkfaka version: 1.0

<?php
$conf = new \RdKafka\Conf();
        $conf->set('group.id', 'elk_consumedeijhelloworld'); 
        $rk = new \RdKafka\Consumer($conf);
echo 111;exit;
echo 222;

the terminal output just 111 and hang up (no response，no exit), the progress is still there why?