@Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
          if (!(msg instanceof ByteBuf)) {
            ctx.fireChannelRead(msg);
          } else {
            ((ByteBuf) msg).release();
          }
        }
Here we add a {@link ChannelInboundHandlerAdapter} to eat all the responses to simulate a
slow dn2.
hbase-asyncfs/src/test/java/org/apache/hadoop/hbase/io/asyncfs/TestFanOutOneBlockAsyncDFSOutputHang.java