void onDequeue() {
      chunksToWriteCount.decrementAndGet();
      chunkWriteStartTime = System.currentTimeMillis();
      long chunkQueueTime = chunkWriteStartTime - chunkQueueStartTime;
      nettyMetrics.chunkQueueTimeInMs.update(chunkQueueTime);
      if (request != null) {
        request.getMetricsTracker().nioMetricsTracker.addToResponseProcessingTime(chunkQueueTime);
      }
    }
Does tasks (like tracking) that need to be done when a chunk is dequeued for processing.
ambry-rest/src/main/java/com/github/ambry/rest/NettyResponseChannel.java