private void sleepIfOverflow() throws Exception {
            if (overflow) {
                overflow = false;
                Thread.sleep(50);
            }
        }
Get producer from cache, create it if not exists.

@param topic - topic name
@return MessageProducer
@throws TubeClientException
inlong-tubemq/tubemq-connectors/tubemq-connector-flume/src/main/java/org/apache/flume/sink/tubemq/TubemqSink.java