private EventStat fetchEventStat() throws Exception {
            EventStat es = null;
            if (!resendQueue.isEmpty()) {
                es = resendQueue.poll();
            } else {
                // wait if eventQueue is empty
                Event event = eventQueue.take();
                es = new EventStat(event);
            }
            return es;
        }
fetch message, wait if queue is empty

@return EventStat
@throws Exception
inlong-tubemq/tubemq-connectors/tubemq-connector-flume/src/main/java/org/apache/flume/sink/tubemq/TubemqSink.java