@Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.channel().attr(IN_USE).set(false);
        super.exceptionCaught(ctx, cause);
    }
The key for whether a {@link io.netty.handler.codec.http.HttpResponse} has been sent for the current response.
gremlin-server/src/main/java/org/apache/tinkerpop/gremlin/server/handler/HttpRequestIdHandler.java