Wednesday, 22 December 2010

A Little Agile nad XP Rant

The title of this blog is "On Languages ... etc etc ... Systems and Proceses", but utill now I never said anything about processes (or did you think I meant UNIX processes?) so let us write something about the latter now. As lately everybody seems to be happy with Agile/XP (like here and here), let's rant about that a little. So beware, it's (at least partially) a #RANT#, so don't try to kill or evangelize me!

1. The Gripes

The one single thing you encounter today in the process land is the Agile. Well, I have a few gripes with that, which I should have wrote up earlier (and I wanted to, really, for the last 3 years or so), but now the time has come. On the other side, now when Agile is mainstream, maybe my points aren't valid anymore? You know, "the normative force of the factual"* :(. Maybe, but let us begin from the start of all that:

As I read the "Agile Manifesto" and the XP explanations some 10 years ago or so, I was just amazed. It was the liberation! And what I particularly liked were things like pair programming, test driven design, and iterative deleopment. But today I must realize that I was somehow mistaken - maybe did I get it all wrong? Somehow it's all different from what I imagined it'd be, and I don't like it very much. Two examples:

a) the pair programming
In my eyes it was all about two people caring about a piece of code, discussing its design, reviewing main rewrites, just because discussing something with another person can show you another perspective on the problem.

And now? The reality? It is crazy, it's about keyboard swapping, and two people doing coding at the same time. For 15 minutes it's my keyboard, and then it's yours. Come on, are we in Henry Ford's car factory? Or were we supposed to be doing some creative work? #RANT#

But there are people who actually like that (here, here) aren't they? I'd say this could work, but only if you are paired up with someone on your level. Not just another beginner guy with a big ego, thank you very much! Even then I find it to be an overkill, 2 people doing work of 1? Aren't there people able to be doing decent work by themselves anymore? #RANT#
b) test driven development/design (TDD)
I liked this idea very much. OK, I've only seldom written the tests before code myself, but there always have been tests for a new feature: either before I coded it or after that. Because really, that doesn't matter if you know what a feature you are going to implement.

But now? The reality? You should always write tests first. Or you are not agile. And why that? It comes even better - TDD can mean test driven design! A good example of this was to find in a blog posting** of the venerable Uncle Bob where he develops a prime factorization algorithm by TDD, i.e. by writing a series of increasingly complicated tests and reworking the algorithm accordingly. That looks for me like crazy, groping in the dark for the right solution, excuse me?! #RANT#

Why should we waste time and rework our solution on and on? The received answer is: because it results in decoupled code. Come on, aren't there other ways to write decoupled code? Like old and unfashionable thinking about its design a little? #RANT#

2. Some Summary and More Gripes

So meanwhile the XP is for me not the freedom, bur rather the next horsewhip of the pointy haired boss types. It's more about following the rules and their religious observance than about anything else. As I read about XP/Agile first, I thought it was targeted at proficient developers, you know, at the responsible adults, which should be allowed to be adult and just do their job! But now I have more and more the impression that it's rather targeted at beginners. Obviously, they need clear rules and directions. So maybe it's about the overall prevalence (and importance) of beginners in our industry?

Well, mabe (just maybe) I'm opposing the abovementioned XP principles because they introduce a process-like quality into XP, and I feel kind of betrayed now? It was supposed to be about freedom and interacting free individuals? Maybe it was just an illusion, maybe the recipe of Agile Manifesto was too simple?

In this this excellent post about "post agile" development Gwaredd Mountain states that no methodology is pure "agile" or pure "process-oriented". Rather, each one of them contains "freedom" (agile) and "process" elements, as a mix of both is needed for the real world. So even the supposedly totally free XP has to have some emergency brakes. Well, so much for my illusions of a better world :(. Nonetheless, the emergency brakes are rather expensive, the double pair of eyes to watch over "Brownian motion" like TDD development? That's my private opinion, but arguably it's somehow taking things to the extreme.

But there's 3rd problem, and it's not easily dismissed:

c) evangelism
In the Agile world-view there's either agile or waterfall, stone age, and nuclear winter. A typical Twitter post says:
Agile change is change. Change is hard for people
thus, if you can't get enthusiastic about Agile it means that you are unreformable, and just can't see the light! I think the Agile trainer guild is responsible for that***. As their training courses target mainly the beginners, they must give them rules to be followed in each circumstances. But I cannot understand why this must be promulgated to the general public? You know, "Only a Sith deals in absolutes", it's not a sign of wisdom do divide the world in the only right way and all the others! #RANT#

Ok guys, you must earn a living, but doesn't engineering decency mean anything to you? Or can't you think for yourselfs and would rather become a follower? Silver bullet anyone? That irritates me, but at the same timee it's interesting - what could possibly be a result of a realy intensive full-night talk with an Agile trainer? #RANT#

It's a little known fact, but Dr. Royce's defining paper for the waterfall process already contained iterations (see figures 3 and 4)! Agile is not that original, people were able to think and use common sense before that! #RANT#

3. So What Do I Think Myself?

You may ask, how should we develop software then? We're not supposed to go back to "cowboy coding" are we? Steve Yegge' post describes an alternative: the pretty informal Google development practices at that time and praises it as the solution. Well I must admit it does sound good, but then even Google wanted to introduce some process not a long time after that (Shh, we are adding a process). In that article they describe how the Scrum process was introduced in the AdSense project (if I'm not mistaken), however not a full embodiment of Scrum. But it seems that somehow for time critical, heavy-money projects you need some kind of a whip in the end... :(

So what do we need a process for? Do we need it at all?

First let me quote Aristotle (via "Pragamtic Programmers" link, and no, I don't read him in original...) - "We are what we repeatedly do. Excellence, then, is not an act, but a habit." As I understand it, we have to kind of design the things which we repeatedly do, if we want to ge good at something. And that's a start of a process.

Staying Alive in Avalanche TerrainThe 2nd insight comes from the field of avalanche avoidance (because I'm somehow of an offpiste skier). What the professionals always do, is to have a checklist in the car and to go through it every time they set off. Because people forget, people do make mistakes, and in that profession, when they do, it can cost them their life. That's a kind of process too - you won't believe that you could do a mistake, but in the grand scheme of things, you probably will. So you need some annoying routine, even if you don't think so!

So what would I take? A methodology I liked rather well was the "Tracer Bullet Development" from the abovementioned "Pragmatic Programmers" book. It's simple, it has a lot of common sense (what I seem to like more then religious fervor) and it goes along the lines of my own understanding of the agile development which I came to during the last 10 or so years.

Because I'm not an enemy of agile. More than taht, I think it's somehow a necessity! In real life there's constant change, and the original design**** of a system cannot be sustained - either it will be dying or it must adapt! So for me, agile has got it right in its basic proposition - you must always iterate. As the ancients used to say "iterare necesse est, vivere non est necesse" :).

And what about my Agile/XP gripes? Here I'm with Steve Yegge - there's "Agile" and "agile", Agile of the trainers and pointy-haired bosses, and agile of the pragmatics. And I'm with the latter.

Waiting for your comments.

* or "die normative Kraft des Faktischen", by Immanuel Kant. This means: all that is, is good, because it is (i.e. exists) or something like that.

** sorry, the original blogpost I read is vanished, this one is the current version reworked as a programming kata:

*** Read Steve Yegge's post about the so called "Agile" experts: "Good Agile, Bad Agile ",, or this one: "Agile Ruined My Life", and look out for the Fraud markers!

**** For example, take this fascinating and/or terryfying case of dying architecture (from the "Refactoring in Large Software Projects" book):
Alas, everything started out so well! The concepts were clear-cut. The technical prototype was a success, the customer was thrilled and Gartner Group decided that the architecture was flawless. Then real life began to take its toll: the number of developers went up, the average qualification dropped, the architect always had other things on his plate – and time pressure increased.
The consequence was that the architecture concepts were executed less and less consistently. Dependencies were in a tangle, performance dropped (too many client/server hops and too many single database queries), and originally small modifications turned into huge catastrophes. To a certain extent the architecture concepts were circumvented on purpose. For example, classes were instantiated via Reflection because the class was not accessible at compile-time.

Saturday, 11 December 2010

Some Observations on Software Estimation

In my prevoius post post in introduced the "real life factor" frw for software estimation, and conjectured it to be as high as 3. I remebered that as I read James Iry's short blogpost. Let me quickly restate its contents. He recollects the course of a software project and the estimates at each point of its history. I summed that up and added the reason for each estimate failure:

             | Project | 
   Estimate  |  Phase  |   Error Reason 
    2 weeks  |    0%   |  initial guess
             |         |  
    4 weeks  |   50%   |  too optimistic!
             |         |  
    6 weeks  |   90%   |  hidden complexity
             |         |  
    8 weeks  |   99%   |  forgotten the tests,
             |         |  docs and review
             |         |  
    8 weeks  |  100%   |  not really ready, but 
             |         |  has had enough!

So there it is, when estimating we are too optimistic from the start, and then we tend to forget a lot of things .So using this error "model" the real life factor would be frw=4! I'd say rather high. Maybe we need a better model? And what if we want to be really careful?

Software Estimation: Demystifying the Black Art (Best Practices (Microsoft))
 When speaking about serious software estimation you will usualy end up with the "Demistyfying the Black Art" book (an excellent book indeed, read it!), and will probably learn and use the PERT technique, where you have to give 3 estimates: the best case, the normal case, and the worst case estimates. Then you take a formula and get the expected project duration.

That's all very well and good, but when using this technique, we still tend to be overly optimistic and to forget a lot of things, exactly as in the above example!

The following blogpost hits the nail on the head:
Our experience has taught us that simply asking developers to make two estimates (“low” and “high”) doesn’t really result in much more information than a single point estimate. Developers tend to be optimistic when it comes to individual estimates. So without a little structure, the “low” estimate usually means the absolute smallest amount of time the task could take – an event with a very low probability of coming true. The “high” estimate means what it’s most likely to take to get done.
Given that data, let us do a smal, back of the envelope calculation for the probabilities of the 3 PERT estimates. Thus:
  low estimate => rather improbable => say 20% probability
  high estimate => most likely => i.e. 50% probability
  medium estimate => will lie inbetween => ~30% probability
So the real life factor for the medium (i.e. realistic) here is frw=3.3, not that different form the above, unscientific guess! PERT will correct this somehow, by not that much. So should we really always multiply our carefully crafted estimates by 3 (or 2), thus admitting that we cannot do it? That's scary.

But wait, we don't need 100% certainty, that would be sandbagging! Let us say, 80% is enough (see Pareto), but that's still 2,7 times the our "realistic" estimate or 1,6 times the "worst case estimate". I don't want to make any conclusions though, it's only some observations because it makes me curious that the value of 3 seems to resurface rather often!

Tuesday, 23 November 2010

Yet Another... Web Framework (in C++)

What? YAWF - yet another web framework? But this is mine(!) ... and it's very small - a Simple Embeddable C++ Webframework for Qt!

1. The need

I have discussed this topic on this blog earlier*, so you shouldn't be surprised to hear about it again: a C++ web framework. You'd think there isn't such thing? Wrong! From my own research and from the comments of friendly internauts I collected a quite a list of possible frameworks:
And recently I found even another one:
  • CppCMS

    Do you see its cool logo? It says that programming in C++ is a good thing, as it isn't hard on the environment, and thus can maybe even stop the global warning ;). I must admit that I never seen C++ from that angle! Interesting point, isn't it? Ok, when you think of all that multicores and figths about cache lines then C++ does quite naturally comes to mind with its very direct memory control, doesn't it? Kind of "lean programming" :).
And don't forget the new kid on the block:

It's rather a wide range of possiblities, so you'd think the world doesn't need another framework, and least at all by yours truly. That's what I thought too, untill I stumbled upon a rather simple problem. Currently I develop a Qt application that runs in the background (call it demon, service, headless, etc.) and would like to have an admin interface for it. Of course I could write a standalone GUI client connecting to the application's command socket but that's so nineties! Only a web interface is fashionable these days. Thus I need a small webapp for the admin console.

So at first then, I thought I'd use some open source code from the above list. But all of them would either not integrate well with Qt events, or require 3rd party includes and dependencies, and gwan would even have to be started as an external server! Well, I didn't use gwan before and it does sound like a border case usage for it, just imagine all that debugging of its servlet compiler in run-time...

Then you may ask: isn't there any HTTP server in the Qt framework? Yes indeed, I found one, but it's an extension of the framework (they call it an option I think...) and it's running as Windows service, not as an additional interface to an existing binary. So we've got the same case as with gwan. BTW, why hasn't C++ a standard HTTP server class? Go has one, Python has one, Javascript has one, but C++ - nope! Well, that's not completely true, CINDER framework has one, and cpp-netlib got one as well, but I wanted to avoid big includes and dependencies like Boost.

But hey, Qt has a couple of HTTP support classes, so I thought: boy, that cannot be that hard! And I just hacked my own mini HTTP server.

2. The design

Of course that gives me an opportunity to design a web framework the way it should be always designed at last :-), because all the others seem to be somehow overcomplex or overcomplicated :-). So let's go down to the brass tacks then!

First we have to decide on the name - let simply try YAWF(4q), and in best software giant tradition I'll use an internal codename, for example "CutieW".

The design will be simple, plain and oldskool, as I need something working and that fast. Besides, never underestimate the power of KISS!

The basic ingredients are the Qt classes for TCP socket handling and HTTP request and response parsing. Then we'll have request handler objects with a process() method. The handler objects (kind of servlets for the Java minded) will have to be derived from a superclass (how uncool, I know) and statically instatiated, so that they can register themself with the server in the startup phase. They register with a name string**, for example "user" or "page", so they can be bound to an URI (see below for the example).

Let's sum it up: there will be a server executable, it will set the URL path configuration in startup phase, each path wil get its own handler. When a request arrives, a fresh instance of the handler will be created, this the handler classes need a clone() method for this.

The server will thus find the matching handler prototype for the URI, clone it, and then invoke its process() method. As you see, there's 1 to 1 relation betweem URI and the handler object in the current implementation, but an extension to "multiple dispatch" isn't difficult, and I'll program it when I have some spare time.

Now to the general usage pattern of YAWF4q. In Clojure you'd write the following:

  (defn display []
(html [:h1 "hello!"]))

(defroutes myroutes
(GET "/" [] (display)))

(defonce server (run-jetty #'myroutes
{:join? false
:port 8080}))
In cpp-netlib this:
  struct hello_world {
void operator()(server::request const &request,
server::response &response) {
// your code here ...
} handler;
  server server_(argv[1], argv[2], handler);;
But in yawf4q it's all pretty plain, non-clever, and almost boring:
  #include "CuteHttpServer.hpp" // the cutie

int main(int argc, char* argv[])
// your application:
QApplication* qtAppl = new QApplication(argc, argv);

// the webserver on port 3100
ibkrj::yawf4q::CuteHttpServer testServer(3100);
string error;

return -1;

// run Qt
The server just starts, finds the config file (using a default, hardcoded name), sets the routes, and waits for requests. If you don't define any handlers, a simple "I'm alive" response is sent back.

3. The example

How to write your handlers? Look, you have to derive them from the TestHandlerBase class. First let us implement the handler of the index page:
  class TestHandlerBase
: public MiniHttpHandler
: MiniHttpHandler("TestHandlerBase") {};
// base overrides
virtual MiniHttpHandler* clone() { return new TestHandlerBase; }
virtual void process(AnalyzerRequest& reqData, std::string& respData);
} g_handler1;
OK that's rather much boilerplate, as we need to supply the name string plus the clone() and process() methods, so maybe I should provide a macro like this:
  // --- OR maybe a MACRO?:
class TestHandlerBase
: public MiniHttpHandler

... your functions ...
} g_xxx;
I don't know, as a matter of fact I hate macros in frameworks! But as an alternative maybe it isn't that bad. Another possibility would be using CRTP, as to automatically add the clone() method, but wouldn't you say this would be somehow too clever when compared with the rest of the design?

And here is the processing method:
  void TestHandlerBase::process(AnalyzerRequest& reqData, std::string& respData)
respData = " TestHandlerBase alive!!!! ";

respData =
"<title>TestHandlerBase is alive!</title>"

respData.append("<h1> Input your user data: </h1><p></p>");
respData.append(testform); // HTTP form for UserName, UserMail and Text, action="person"

respData += "</body></html>";
OK this doesn't look very cool, but the view component isn't yet there, wait a little. What this handler does is to ask for some user data. Now the second handler follows, which will processes the submitted user data:
  class TestHandlerPerson
: public MiniHttpHandler
BASE_TEST_HANDLER_FUNC(TestHandlerPerson); // here process() is already defined

} g_handler2;

///////////// impl:
void TestHandlerPerson::process(AnalyzerRequest& reqData, std::string& respData)
respData =
"<title>TestHandlerBase is alive!</title>"

respData.append("<h2> Thank you for your data! </h2>");

// parse the data for display:
map<string,string>& data = reqData.formularData;
map<string,string>::iterator iter;

"<table border=\"1\" width=\"70%\"><tr>"

for(iter = data.begin(); iter != data.end(); iter )

respData.append("<p></p> <a href=\"/index.html\">Back</a><br>");

respData += "</body></html>";

Rather grotty servlet or .jsp style here, isn't it? Mixing presentation with code?!

Don't despair, you can use a template. Yes, let's be modern! I chose the mustache :{{ template syntax. I decided for mustache, well, because it's pretty new, generates much buzz, and isn't looking too bad. For those who don't know mustache, it is a simple HTML templating syntax with values encoded like this:

and sections, which can be rendered multiple times, if they receive a list as input data:
{{value1}} => {{value2}}
So there's no need to code anly loops in the template. YAWF contains an implementation of mustache :{{, which seems to render correctly all the examples I found in the online mustache docs. The implementation is based on a simple idea: the template is parsed into a linear sequence of "nodes", and the data items passed to the template take care of rendering and walking the node list. Have a look at the source code*** if you want.

So our response handler would now look like this:
  // using templating:
#include "CuteMstchData.hpp"
void TestHandlerPerson::process(CuteSrvRequest& reqData, std::string& respData)
string templ =
"<html><head><title>TestHandlerBase is alive!</title>"
"</head> <body> <h2> Thank you for your data! </h2>"
"<table border=\"1\" width=\"70%\">"
"<tr><th><b>Field</b></th> <th><b>Value</b></th></tr>"
"<tr><td> {{field}} </td> <td> {{value}} </td></tr>"
"<a href=\"/index.html\">Back</a><br>"

// convert data to JSON represenation:
map<string,string>& inpData = reqData.formularData;
map<string,string>::iterator iter;
int i;
ibkrj::yawf4q::CuteMstchValMap templData;

for(iter = inpData.begin(), i = 0; iter != inpData.end(); iter++, i++)
templData.addToList("datatable", i, "field", iter->first);
templData.addToList("datatable", i, "value", iter->second);

// display page with data (the View of MVC)
respData = CuteHttpHandler::renderThis(templData, templ);
It maybe doesn't look much better than the plain HTML code, but here we could save the template in file, and read it in at the runtime. And we've got the View part of the MVC pattern. The handler objects stand for "C", but so far don't have support for "M" in YAWF4q.

Now, as last part of the puzzle, we have to configure the server paths, but this is simple:
# test configuration

index.html$ :: TestHandlerBase
person/.*$ :: TestHandlerPerson

You see, regular expressions are supported. Now let it run baby! The first handler gives us:

Then we willingly give our data:

And see the results:

4. Summing up

At the moment the code*** is only very basic, as I haven't got time to work on it a much as I'd like. I wrote it on my private time, as my customer did decide in favor of a general, grand-scheme, system management solution. So as for today, I wrote only a single test, that one which was described above, and tested it with Visual C++ on Windows. YAWF isn't more than a toy just now as many features are simply missing, for example I'd like to have a built in support for configurable error pages to round the things off. And as next thing, I'd like to add the Model component using my CuteWorkers framework (I hope I'll come to write a post about Qt-workers too).

But there's much more that could done, like:

- HTTPS support in the sever (that shouldn't be very difficult as Qt offers QSslSocket and other classes)
- cookies and session data handling
- dynamic loading and caching of the templates
- dynamic loading of the servelts vial DLL (kind of what ASP is doing)
- a "Clojure example" like dynamic interface

and so on, and so on. Look at my TODO list in the github repository. Nonetheless it's simple (KISS!), it's pluggable, it doesn't have any dependecies other than Qt. Requirements fullfilled!

* check out these previous posts: servlets-in-c.html, c-servlets-again.html, c-server-pages.html

** we cannot forget that C++ hasn't much to offer in terms of introspection. But we won't give up automatic registration and detection of handler prototypes!

*** You can find the code at Github:

Saturday, 13 November 2010

Engineering Decency

A couple of days ago I was quite unpleasantly touched by a tweet (a Twitter tweet :-) of a so called "expert" (you know, one the people doing only presentations and learning new languages to write their next book...) ridiculing a developer about a failed project. Somehow I didn't like that - come on, the guys just tried to capitalize on a promise Google (yes, that big engineering powerhouse) made! And they were not alone...

What is that, that the programmers find it so hard to show some engineering decency? I've seen it again and again. Is it so much fun* to flame someone to feel better? The experts should know best that doing stuff mean means making mistakes. Or maybe have they forgotten how it is to be working with real stuff instead of powerpoint metadata?

If you are skiing difficult terrain, you know that the question isn't if you will fall, the question is when you will. That's the same in software - you don't want to believe this now (and me neither) but you will make (sometimes stupid) mistakes! So please, show a little decency. The guys you are going to deride probably just tried to create a working system for a given set of requirements which then turned out to be largely false and for a specific platform, which then emerged to be broken. We've all been there.

And because it's difficult and needs to be learnt, I have an example of how to exercise engineering decency (found here). Instead of the usual:
What idiot with even half a handful of moldy cottage cheese for brains would ever create a pile of stinking filth like this and call it an application?! The true feat of engineering here is that this code monster didn't swallow your whole organization in the black hole of its utter lameness. Where did this person learn programming — NBC?”
Try saying that:
“This will take me longer than we had discussed. In my initial examination of the system, I missed some design decisions in the existing code that conflict directly with what we need to accomplish. I didn't anticipate the approach adopted by earlier developers, because I would not have designed it that way myself. I’m sure they had their reasons for choosing that direction, but so far those reasons have eluded me.”
That's decency, that's humility. Maybe there's a reason you just don't see now. But even if that's really a load of crap, frankly, who of us can say he never ever wrote bad code (or a bad powerpoint presentation for that reason)?

* well, if we'd like to get Freudian, we could say that the unconscious fear of doing some big, stupid mistake reveals itself by attacking others, and that we can maybe reason from that, that the majority of programmers are not well trained for their job. But that would be only a mere speculation to discuss with friends on a lazy evening...

Monday, 16 August 2010

Named function arguments for C++

For me a high quality code is a readable one. Consider a hypothetical method like this:
  class XXX:
void func(int aaa, string bbb, bool optionX = true);
now try to call it:
  func(1, "test", true);
What irritates me here is, that I don't know what exactly does true mean at the first glance! Thus I found myself quite often writting code like this:
  bool useOptionX = true;
func(1, "test", useOptionX);
Well, that's better, but what about this:
  bool useOptionX = false;
func(1, "test", useOptionX); // should I use it or not?
a little bit misleading, isn't it? Not that this would be a big problem, but it's nevertheless a small hitch obstructing us from reading the code effortlesly. OK, next try:
  bool dontUseOptionX = false;
func(1, "test", dontUseOptionX ); // don't use is false, so I should use it?
A total mess! And what about constructors?
  class XXX:
XXXX(bool optionY);
  class YYY: public XXX
YYY() : XXX(true) {}; // true what???
Call me pedantic, but I don't like that at all! What we really need here are Python's named arguments:
  sameFuncInPython(aaa=1, bbb="pythonistas", optionX=True)
Simple, effective, readable! Is there a way to emulate this in C++? Recently, as I was especially annoyed with the constructor example from above, I devised a following solution:
  class XXX:
XXXX(bool optionY);
typedef useOptionY bool;
  class YYY: public XXX
YYY() : XXX(useOptionY(true)) {};
and now the other code can be wtritten totally plausibly too:
  typedef bool useOptionX; // local namespace!
  func(1, "test", useOptionX(false));
func(1, "test", useOptionX(false));
and what would you say to the following?
  waitOnSocket(sec(1), usec(20));

Small thing, but it improves my source code. I like it!

PS: After I wrote this, I remembered reading something in this vein about Java. And really, this post by Codemokeyism proposes generally the same solution:

  new Customer(firstName("Stephan"), name("Schmidt")); 
Alas, instead of a benign typedef, you have to write a whole new class named name and firstName etc. Without doubt it's and improvement, but the costs and the clutter... But on the other side Java tends to be verbose nonetheless, so maybe it's OK.

Monday, 14 June 2010

Javascript on the server?

Recently, I stumbled upon an iteresting presenation about server I/O parallelism and multithreading. Surprisingly it was in a Javascript conference, as I sometimes have a look at the Javascript language developments. I'd never expect to find something like that in this contex though.

The general message of the presentation was that threads suck and asynchronous programing is the king. Come again? I don't quite agree with that (or rather agreed, as you'll see in brief) - wasn't that for the threads to save us from the onerous asynchrounous programming with its context information and callbacks (remember Windows event programming?)! The threads justly delivered a convenient abstraction to group the logically connected data and logic in separate units of execution. So now we are doing a full circle: from asynchronous to threads to asynchronous?

OK, on the surface that may be looking like that, but there's more to that. The problem is that when we apply threads to parallel I/O they are just to slow (you know, context switching, thread stampedes and all that). Thus there's a host of asynchronous I/O methods starting with the venerable select() UNIX call. Ok, agreed, for that special field the threading model isn't very appealing, but for the general usage I'd just hide this inside of an I/O thread...

Now there's this pesentation (Ryan Dahl’s talk on Node.js) and what the author says is exactly that: callbacks and asynchronicity are good! How that? We all know it's a pain in practice? His response (an this is the valuable insight got when watching this) is that we just didn't have a good enough programming language to realise that! When you do in in C (as you'd likely to do when programming performant I/O) you are messed up, but if you take Javascript...

See, that's the crux here: Javascript was designed to work in a callback driven environment, so the language has unique mechanisms which no other language can offer. Thus if we take Javascript and do event oriented programming it's a breeze then! The idea is to take the ultra higspeed C library (libev in that case) and wrap it with event-friendly Javascript hull. Here's an example code from node.js site:
  var net = require('net');
net.createServer(function (socket) {
socket.addListener("connect", function () {
socket.write("Echo server\r\n");
socket.addListener("data", function (data) {
socket.addListener("end", function () {
}).listen(8124, "");

Well, maybe it isn't a thing of beauty (if you're not into Javascript) but it's concise, everything is at one place, and you can read it without reading tons of manuals first. So maybe this is the way of doing this? Another thing I liked that node.js never provides a blocking API - even filesystem calls are asynchronous! That's consequence!

Sorry for the short post, but it's summer, I want to go out and watch some worldcup!

1. the talk to be found here:
2. and here's the code:
3. if you'd like some more technical details, here's an excellent post by Simon Wilson:
4. node.js critique (yes, there's such a thing too!):

- here is a simple blog engine in less than 200 lines of code using node.js : Not bad, I'd say.
- Multi-node: how to implement a concurrent node.js HTTP server:
- Hummingbird: an impressive application based on node.js -

Sunday, 13 June 2010

Software estimation and re-reading the classics

Recently I stumbled upon the "Software Top-Ten List"* again. At first I though, OK, that's old, they did mainframes at that time! But then I read it nonetheless. Maybe because it's so short? It's only 3 pages. Whatever. I read it I was surprised about how refreshing it was. Not mouldy, stale and irrelevent, but interesting and fresh! Surprisingly, because the findings are supposed to be well known.

One interesting thought came after I read the point 8:
Software systems and software products each typically cost 3 times as much per instruction to fully develop as does an individual software program.
I immediately thought about that old estimation rule: estimate how long it will take to be done, and then multiply it by two. I always though it to be unserious or a manifestation of intellectual laziness. What, you aren't able to say how long this effing program will take to be written? Just sum up the parts (as shown below)!

But let's look at the problem from a little more different angle: what if programmers do not take into account the costs of polishing the program, making it user-friendly, plus all the problems and dependencies from other programmers located in other deparments of the company - "L'enfer, c'est les autres"! Normally you do not take this factors into account when estimating, and you even cannot estimate it properly. We use either a brute-force 20% project buffers or a statistical estimate based on the PERT method, but it somehow doesn't work out that good.

So maybe we should take the above citied measurement data, at use it when estimating? Just multiply our technical-only estimate by the "real world" factor? Personally, I still cannot believe that the "real world" factor be so high as 3! Am I too optimistic? But I think that frw=2 should be a good choice!

Although I'm a little afraid here, as I always imprement a given piece of code faster than my own PERT estimate. But recently, when estimating the entire system, I missed the point completely: new requirements, unexpected dependencies on not so great libraries, the internal pressure to please the customer... This all sums up in a greater project! An at that point I should have been to muliply so high as by 4! Welcome in the real world.

* Harry W. Boehm, "Industrial Software Metrics: A Top-Ten List",

Thursday, 29 April 2010

Bug hunting or how dumb can you get, really?

As a programmer you sometimes can't help but feel really stupid! Really stupid-stupid! Look at this code snippet for example of a foolish bug that kept me busy for some time. The story behind this is that I added a feature to the product I'm writing for a customer, and was totally happy with it. There was a real customer benefit and it worked like a charm through my tests. However, when deployed to the internal test system, it crashed unexpectedly now and than.

That was a kind of shock, because the product was running stable for more than a year in this environment, and I was totally unsettled as I didn't want to believe that the new feature could have something to do with it. It was tested rock-solid. There must be a mysterious bug somewhere else in the program. And it hid for one year before it disclosed its identity! Bad!

However, after I ran the collected test data on my development machine, it turned out to be a pretty uncomplicated bug:
    for(size_t i = 0; i < a_prInput->frameCount(); i++)
        // header
        size_t start = a_prInput->NettoDataParts[i].uOffset;
        size_t pos = start;
        DnsHeaderData header = parseHeader(a_prInput, pos);
        // interesting data there?
            TRACE("dns: packet isn't a response, ignoring...");
        // skip the questions
        for(int i = 0; i < header.questions; i++)
            if(!parseDnsName(a_prInput, start, pos))
                TRACE_ERR("dns: cannot parse a question record");
                m_uGoodByteCnt = pos - a_prInput->NettoDataParts[i].uOffset;

You see? The code was referencing the data form the outer loop with the index of the inner one! And it did it only in error case, and crashed only if it was out of luck. Arrgh... There was no problem with fixing this, but it started me thinking: I'm programming for some 20 years, I know C++ in and out, why did I make this bug in the first place? Did I violate some programming rule or best practice? Is it possible to avoid such bugs by some sound practices? Some answers come to mind:
  1. There should be a warning from compiler
    That would be the ideal solution. But what warning should that be? And what if I really wanted this that way? I'd need to use an ugly #pragma then? No, better let it be.

  2. I should have used at()What should I say, er, well, at() is for wimps! And if that wouldn't be the case, we have a choice between at() and the [] operator. So we want to excercise our rights!

  3. Use telling names
    Well, of course, I could name each loop variable accordingly, but come on, can you imagine the hassle? Because if this has to be of any good you have to be consequent. So maybe only do this for nested loops? Maybe, but if I start to do this as to avoid this error, and something else to avoid some other error, you guess it, it becomes a pain! We need something more general,
  4. Use for_each(), as we don't do any addressing here
    That's more interesting, as logically speaking, the inner loop isn't indexing single elements, but rather wants only to skip over the uninteresting headers. But, on the other side, for_each() is annoying, as it requires start and end of the sequence, which isn't a problem if I'd use the iterator, but gets pointless if I never want to use the iterator directly!

  5. use iterators to go high level
    Isn't that the same as the above? No, because it's not an application of a specific technique in a specific situation, but rather a conscious decition for rising of the abstraction level. And quite serendipitously we can avoid the above mentioned error! Or are we? What if both outer and inner loop are using the same name for the iterators? Here we are agan back on the square one and have to use for_each() for the inner loop as to be safe.
Alas, none of them is satisfactory. Well, I know, there's one more solution: code reviews (or pair programming). But first, my customer isn't doing them that often, and second, I doubt this bug would be found in a review/pair. But even assuming it would be found: the price is much to hight! It took me a couple of minutes to fix it, once I had the right data, and my customer expects "results just now".
What is the key point? What does this all mean? Are we doomed? I think that there are two possiblities here: either use iterators or some other high level constructs (which admittedly is somehow of an overkill), or be prepared for occasionally fits of stupidity. In the end we are only humans, and errare humanum est... And who wants to be safeguarded against everything?

PS: Sorry, I started this entry long ago, but in the meantime I was so distracted that I couldn't come round to write anything for the blog. Besides, microblogging isn't doing it any easier ;-).
PS2: Other possibility: write shorter functions, use a skipNameRecords() method and you are saved! But really, that function is under 1 page lenght, How long should functions be? Five lines or so? Or seven as adjust to humain brain's cognitive limitations?

Sunday, 28 February 2010

Fooling the ODR (and the compiler)

I just discovered a technique that is prety convenient but rather not self-explaining, nonportable (?), and possibly a maintenance nightmare. So you should never use it, should you? Except, as it's sort of cool, if you'd like to go a little on the geeky side...

1. The need for speed

Imagine you are writing some quick classes in the Java style (i.e. no header files), locate them in some C++ source file, and forget about them. Then you discover that you need to refactor your program (in my case it was a custom test framework) and to move some classes out to a separate file (a.k.a. compilation unit). Now you shun to do the right thing (i.e. to refactor) because you'd have to cut up your classes in two: the .h file and the .cc file, and to duplicate some (non always trivial) amount of code. So yo aren't doing that...

But stop, following trick did it for me: I defined the classes in a separate .h file and kept the .cc file with the extracted classes unchanged. I included the new .h file in the rest of the old .cc file where the classes were removed from. Then I just linked the the whole thing, et voilá, everything worked like a breeze - a refactoring as we like it!

2. Why does it work?

But wait, we spared some editing work, but didn't we violate the One Definition Rule of C++? I'd say we did. So why didn't the compiler complain? Well, as to answer it, we've got to look at the example a little closer.

The extracted classes looked like that:


  #include "WorkerThread.hpp"

// test thread A
class ThreadA : public WorkerThread
} g_workerA;
  // test thread B
class ThreadB : public WorkerThread
} g_workerB;
Note that there's no TestThreads.hpp definition file here, thus we don't have a direct ODR violation for the compiler to complain! The newly created definitions file TestThreads.hpp looked like this:
  #include "WorkerThread.hpp"
  class ThreadA : public WorkerThread
virtual void addRequest(Request& r);
  class ThreadB : public WorkerThread
virtual void addRequest(Request& r);
The WorkerThread.hpp definition file looks like this:
  class WorkerThread
virtual void addRequest(Request& r);
And the rest of the TestMain.cpp file where the TestThread classes were previously placed:
  #include "TestThreads.hpp"
  extern TestThreadA g_workerA;

extern TestThreadB g_workerB;
Can you see why we could fool the ODR? Well, in this special case we didn't used the constructors directly in the TestMain.cpp file, only the methods of the WorkerThread superclass which then call the appropriate virtuall methods defined in the ThreadA class.
The linker then generates a reference to the virtual ThreadA::addRequest() method. Well, guess what, a method with the very name can be found in TestThreads.cpp, and the linker can resolve it no probs!

Although we clearly have two definitions of the ThreadA class, we get away with it! The ultimate reason for that is that the C++ compiler doesn't have the global knowledge of the whole program - it works only on the compilation unit level, and the relinquishes the responsibility for the complete programm to the linker! I.e. there's no whole programm optimization possible (at least not in the standard model, although Visual C++ compiler can do it).

3. How to extend the "hidden" classes?

Suppose we'd like to call a new method in the TestThread.cpp file from the outside. You cannot call this method directly, as we do not include the real definitions of the TestThread classes, but only the "fake" ones. Alas, there is a price to pay for fooling the compiler and for beeing lazy! The price here is, that we have to modify the base class (TestWorker.hpp) by adding a new public virtual method, if we need a new TestThreadA method to be called in the TestMain.cpp file!

Not pretty, uh? You know, sometimes you can go away with breaking the rules, but in the end you'll have to face the consequences. In the art of software design, your skills are measured at your ability to estimate for how long you will go away with laziness and tricks, and when you have to resort to the known, sound and boring "best practices".

But nonetheless, the price I had to pay was OK for the deeper knowledge of the compiler-linker cooperation and the increased knowlede of my own code.

Sunday, 14 February 2010

Do you GoF - the belated anniversary and the ladder

Last year we had the 15th (or so?) anniversary of the seminal "Gang of Four" book. Is it that old already? So maybe discussing the design patterns is all an old and boring stuff now? Well, shame on me, I wanted to write up my ideas on that matter for such a long time that I run the risk of them beeing irrelevant. But on the other side it's a kind of unfinished business for me, and I have a to kind of close it up.

Some time ago I wondered - why didn't I use the design patterns that much in my programming and design work? I came to the conclusion then, that the design patterns are useful as a common vocabulary as to speak about designs, but then some new ideas surfaced in my mind. By the way, why should I use a pattern vocabulary if I don't use any patterns in my designs?

1. Ideas from chess and math

If you're playing chess (need a Wikipedia link here? ;-) you are accustomed to seeing the board in patterns: check-mate patterns it is! You try to imagine what kind of a check-mate setup could be possible in a given situation, and then work towards that by moving your pieces and trying to chase away your opponent's pieces as to complete the pattern you have in your mind. I must admit that I never had this feeling when writing software. Some pattern in my mind which is the solution for some design problem? Nope.

Read the "Refactoring to Patterns" book by Joshua Kerievsky? When I first heard of the book I though he struck the right idea: only use patterns to refactor code which is a mess. But then when actually reading the book, it was rather a feeling (in most cases) of doing something wrong to the code, well, like overengineering it! So the book didn't reconcile me with patterns too, as it didn't give me the chess-like feeling of a pattern just matching a given situation.

The other problem with patterns is their presentation. This overly formal template with "Forces" (why not just problems?), "Intent", "Consequences", etc, etc... This makes me think about "The mathematicians lament"* - where a matematician reproaches his fellow scientists of over-formalization of mathematics with the effect of its incomprehensibility. What he is saying is basically the following: yes we need the formalism, but only in some very difficult cases where our intuitions don't work. But not in every and one case: "nobody's dying here!"*, you can relax a bit!

It's the same with patterns: the stern formality of presentation is both somehow comical and making the contents rather indigestible, and an dry, uninspiring read. I can only say, relax, we are not deliberating about the meaninig of infinity like Cantor did! We are just describing some not so complicated techniques of object composition! Could you stop to be so pompous?

2. Dreyfus et al.

Do you know the Dreyfus model of knowledge acquisition**? It defines several phases in learning a specific skill: beginner, advanced beginner, competent, proficient and expert. Beginners need rules and recipies, competents can continue learning on their own, proficients and experts see the big picture and fly by the seat of his pants.

Where do the design patterns fit in this scheme? Well, at the beginner level they aren't useful, as they are not "step by step" recipies. On the other side, for the proficients and experts, they are some kind of rules, and experts do not like rules and recipies by definition!

I personally think that patterns appeal rather to the lower ranges of the skill spectrum. Did you see the hopelessly overengineered software full of design patterns written by the beginners? I've seen it only too often!

So maybe they are for the competent? And the usage by competent and proficient users? Let me tell you a little story here. It's not entirely true that I don't use patterns! Lately, I thought that I could warrant the use of the visitor pattern in my current product, as to extract the reporting aspect out of several content managing classes. Well, it has a kind of worked at first, but now, as this whole aspect has to be redesigned, I noticed that this design is rather unintuitive and I cannot simplify the reporting without dumping visitor first. Ok, experiment failed, but my initial problem was that I didn't really search for a solution of my problem, but rather stopped at the point where I found the (as I thought then) matching design pattern! But I didn't think it trough as thoroughly as I should!

3. Summing up

So maybe the thing with patterns is that they are like the "Wittgenstein's Ladder"? You know, what he said in his "Tractatus Logico-Philosophicus" (I cite from memory):

...this book is like a ladder, use it, but then throw it away.
Isn't it the same with patterns? Use them to expand your experience, but don't use them in your software! And as to make the discussion complete, let us state a completely different point of view, a Lisper's critique***:
When I see patterns in my programs, I consider it a sign of trouble. The shape of a program should reflect only the problem it needs to solve. Any other regularity in the code is a sign, to me at least, that I'm using abstractions that aren't powerful enough-- often that I'm generating by hand the expansions of some macro that I need to write.

This is the typical smug Lisp programmer assertion, as they mean that all other languages will in limes converge to Lisp, but newly I tend to think along the lines of the Lispers: the design patterns are a fix for lacking feature in language A, which you know from language B. But as we cannot change the language in most cases, and we are doing OO in the mainstream, just mind the ladder parable!

Update (June 2010): There's another explanation which I didn't think of before. I came across that when reading some programming book (which I cannot come up with now, sorry for the author!). Recall the mid 90-ties: it was the time of the "object craze", everybody wanted to be part of OO. But nobody really understood OO, and as the book went "Stroustrup gave us the C++ but he didn't tell us how to use it"! Her come the patterns, a kind of missing OO manual! This would explain my feelin that half of them was trivial (or not so difficult to figure them up by yourself) and the other half was implemeting language features missing from C++. Very sober diagnose, but at the moment it's my favourite.

* Paul Lockhart, "A Mathematician’s Lament",

** I found it in the book of Andy Hunt, "Pragmatic Thinking and Learning", Pragmatic Bookshelf, Oct. 2008, but here's a blog post link, and here another one

*** Paul Graham, "Revenge of the Nerds",