@Override
        public void channelInactive(ChannelHandlerContext ctx) throws Exception {
          promise.tryFailure(new IOException("connection to " + dnInfo + " is closed"));
        }
Helper class for implementing {@link FanOutOneBlockAsyncDFSOutput}.
hbase-asyncfs/src/main/java/org/apache/hadoop/hbase/io/asyncfs/FanOutOneBlockAsyncDFSOutputHelper.java