code: public void recordCheckoutQueueLength(SocketDestination dest, int queueLength) {
          if(dest != null) {
              getOrCreateNodeStats(dest).recordCheckoutQueueLength(null, queueLength);
              recordCheckoutQueueLength(null, queueLength);
          } else {
              this.checkoutQueueLengthHistogram.insert(queueLength);
              checkMonitoringInterval();
          }
      }
docs: Record the checkout queue length
  
  @param dest Destination of the socket to checkout. Will actually record
  if null. Otherwise will call this on self and corresponding child
  with this param null.
  @param queueLength The number of entries in the "synchronous" checkout
  queue.