question: private void enqueueSend ( ) { final int currentOutstanding = outstanding . get ( ) ; if ( currentOutstanding < concurrency ) { sendBatch ( ) ; return ; } pending = true ; pendingTopics . offer ( this ) ; listener . topicPending ( Publisher . this , topic , currentOutstanding , concurrency ) ; sendPending ( ) ; }
target:  Enqueue this topic for batch sending. If the request concurrency level is below the limit, send immediately.