code: public void progress(long amount) {
          Entry e = flushedEntry;
          assert e != null;
          ChannelPromise p = e.promise;
          long progress = e.progress + amount;
          e.progress = progress;
          if (p instanceof ChannelProgressivePromise) {
              ((ChannelProgressivePromise) p).tryProgress(progress, e.total);
          }
      }
docs: Notify the {@link ChannelPromise} of the current message about writing progress.