Question for KafkaRequestHandler

[阮良]

Hi Folks, 
   I am confused about the code below ，why the IO thread set the daemon ?   
in my thought , daemon thread is not suitable for some importment work 


def createHandler(id: Int): Unit = synchronized {
runnables += new KafkaRequestHandler(id, brokerId, aggregateIdleMeter, 
threadPoolSize, requestChannel, apis, time)
  KafkaThread.daemon("kafka-request-handler-" + id, runnables(id)).start()
}