multiple consumer in one process will cause poll() block?

[jixushui]

when multiple consumer in one process, each consumer invoke poll() will block server minutes.

consumer1 = KafkaConsumer(topic1, client_id=topic1, bootstrap_servers=KAFKA_SERVER, consumer_timeout_ms=1000, group_id="group_test")
consumer2 = KafkaConsumer(topic2, client_id=topic2, bootstrap_servers=KAFKA_SERVER, consumer_timeout_ms=1000, group_id="group_test")
consumer1.poll() # this is ok
consumer2.poll() # this will block server minutes

the environment and config is one zk, one broker, one partition per topic

can any one help?
Thanks