參考文獻：https://docs.confluent.io/current/clients/confluent-kafka-python/index.html#consumer

• Producer.poll(timeout)

　　timeout(float) – Maximum time to block waiting for events. (Seconds)

　　Polls the producer for events and calls the corresponding callbacks (if registered).

• Producer.flush()

　　Wait for all messages in the Producer queue to be delivered. This is a convenience method that calls

• Producer.poll()和Producer.flush()的區別：

　　flush確保所有meg都傳送給broker，對poll的不停呼叫直到len(Number of messages and Kafka protocol requests waiting to be delivered to broker)為0.

• Consumer.poll(timeout):

　　Consume messages, calls callbacks and returns events.

　　作用是取資料，傳入的引數：timeout(float) – Maximum time to block waiting for message, event or callback. (Seconds)是等待訊息到來的最長時間。