code: @GuardedBy("lock") protected void sendBundledMessages() {
          for(Map.Entry<Address,List<Message>> entry: msgs.entrySet()) {
              List<Message> list=entry.getValue();
              if(list.isEmpty())
                  continue;
  
              output.position(0);
              if(list.size() == 1)
                  sendSingleMessage(list.get(0));
              else {
                  Address dst=entry.getKey();
                  sendMessageList(dst, list.get(0).getSrc(), list);
                  if(transport.statsEnabled())
                      transport.incrBatchesSent(1);
              }
          }
          clearMessages();
          count=0;
      }
docs: Sends all messages in the map. Messages for the same destination are bundled into a message list.
  The map will be cleared when done.