ASSERT(AfxGetThread() == NULL) with VisualStudio 2010, or the DLL-hell, revamped

Everybody thinks DLL-hell is a thing of the past. Me included: #WTF, just start the Dependency Walker, look what libraries got loaded, correct it and be happy*. Not so, with the advent of Visual Studio 2010 everything got a bit more complicated!

Let me describe the problem which I encountered working in a project for one of my customers. Let's start with a...

Disclaimer:

This is only a short technical note - for those who (like me) first check the Internet for solution to weird programming questions!

The Problem:

is maybe best described by this desperate post:

Hi all,

I have a question to solve, the situation is I use a exe to load a dll(MFC regular dll),but when I use LoadLibrary() to load the dll and in the constructor of the object whose base class is CWinApp in the dll, It have a assert error, and the code line is ASSERT (AfxGetThread() == NULL).Is there anyone have the similar situation with me and have thoughts about it can tell me ,we can talk about it.

thanks in advance.

Well, the same happened to me when I was porting a C++ application from Visual Studio 2008 to VS 2010. To be honest, the situation was a little more complicated: a mixed mode C++/C# program using C++/CLI as a glue. But back to the problem: the standard explanation for that ASSERT is that you have forgotten to include the AFX_MANAGE_STATE macro (Reason 1) in exported DLL functions as described here.

Sadly, this wasn't my problem. It applies to non-MFC DLLs only**, which mine wasn't, so the whole module state management business should be cared automatically in DLL initalization code the linker is generating. This again is controlled by #define macros used whith the compiler (like _USRDLL, _AFXDLL and their hellish likes). So maybe this could be the reason? Nope, everything was correct :-(.

After more web-searching and finding only tons of happless cries for help I stumbled upon the 2nd useful link

Sounds like you have two or more CWinApp objects, and they're using the same AfxGetThread data. I suppose this could happen if your libraries are linking to different versions of MFC, including mixing of debug and release versions. You might use Dependency Walker (depends.exe) to determine the DLLs you link to implicitly, or the Sysinternals Process Explorer to determine the DLLs you're using at runtime

Well, that sounds interesting, mybe I've mixed debug and release DLLs? Nope (although I made that error later on, so it's defintely a good point to keep in mind (Reason 2)). What could it possibly be then???

The Solution:

The solution is more complicated, but somehow both typical and symptomatic for real-life nontrivial system using Microsoft technology... As my client had a really old codebase growing steadily with the years, all possible Microsoft technologies could be found there; beginning with plain old DLL, through MFC-based ones, further using C++/CLI and at last arriving at C# and .NET. This last one was burdened with a constraint: we had to use .NET v.2.0. The problem is, that Visual Studio 2010 doesn't suppport .NET 2.0! Because of time shortage they decided that only .NET 4.0 will be supported out of the box, and that the 2008 VS-compiler will be inegrated in Visual Studio 2010 to be used for older .NET versions.

Well, in itself it wouldn't pose any problems, if there wouldn't be the C++/CLI code which we used as glue between pure C++ MFC and the newer C# parts. It has to be compiled for the .NET 2.0 as well, thus should use the 2008 VS-compiler. But it is put in a DLL which int turn is loaded by a traditional C++/MFC one (created with  2010 VS-compiler!). See it? Two different compilers, 2 diffrent runtimes, 2 CWinApp objects as in (Reason 2) (or maybe the loader gets misleaded, I'm not sure about it). In any case, Visual Studio 2010 is forcing us to use 2 compilers in one application here (Reason 3).
 

The Mores:

I'm not sure about that one. How about this: stay away from MFC and use Qt? Or: don't migrate your code to VisualStudio 2010 (as it's rather slow to boot)? You're damned if you have to be backwards compatible? 

--

* see here  for author's previous letter from DLL-hell

** more hellish details: 3 kinds of DLLs you can use on Windows: ... TODO: link (but that's just plain boring!)

DSLs not so pointless?

... or: busting myths and fallacies, this time - the DSL-s!

Until recently I'd only sneer at the idea of DSL's: what the @!%*, either we have a soild API for developers, or a specialized higher level language for the specific task. And the higher level language best shouldn't be  done at all, because the non-technical user just wants a smooth GUI to click his requests together! So spare your DSL hype on me, go and find another gullible middle management person.

But then I read the following passage and the fallacy behind this reasoning became apparent to me:

In other environments I could write tests together with the product owner. Together, we could create and discuss tests that expressed what we wanted our code to do without getting buried in the details. The tests I wrote in C++ were quite unreadable for a non-C++ developer.

What was my error? DSL isn't meant as a programming language, neither for the developer, nor for the notechnical user - it is meant to document things!

Look at the following example of a testing DSL in C++:

  #include <igloo.h>  // testing framework*
  #include <cell.h>   // tested class
 
  using namespace igloo;

  Describe(A_Cell)
  {
      It(should_have_coordinates)
      {
          Cell cell(3,4);
          Assert::That(cell.getX(), Equals(3));
          Assert::That(cell.getY(), Equals(4));
      }

      It(can_detect_if_its_a_neighbour)
      {
          Cell cell(1,5);
          Cell neighb(2,4);

          Assert::That(cell.isNeighbourTo(neighb), IsTrue());
      }
  };

You must say it's a piece of C++ code** you could show to anyone and discuss it as a kind of formal spec. You and your partner don't have to learn Z or some other specialized notation. What both of you know already is just enough to bridge the gap. And it's cool code as well!

--
* see: http://igloo-testing.org/
** it's not a joke, all this is possible in C++

Geeky Halloween costumes...

Matching nicely my last post abot the Go language: dress up as a programming language mascot:

(as appeared in  Golang blog).

Any other languages to follow? For Perl it's simple (a camel), for OCAML too (a supercharged camel), but what about C++? Or Assembler?

PS: My favourite C++ pic is this:

. But you really can't dress up like that, can you?

What I did like about Go.

Last week I've read the "Learning Go" book. I did that by sheer coincidence: it happened that I had the (free) book loaded on my eBook reader and just looked for light but interesting read. Why not an intro to a new programming language? So I started to with it and I didn't regret my decision. It was an entertaining and interesting lecture. I'd like to describe here what I liked about the language.

See, normally reviewers concetrate on what they didn't like in a language, but I think that's way too easy! The things we don't like are most probably the things we aren't accustomed with, and with some experience they wouldn't annoy us any more. So don't gripe, just be easy on Go!

As I learned from the book, Plan 9 project*, the (supposed to be) successor of Unix, included a language called Limbo which was a lot like Go already, which built on an earlier langauge called Newsqueak. So surprisingly, there's a lot of history showing up here!

Go itself is like it's mascot (look to the right!): small and quick. It's compiled and statically typed but does type deduction (like OCAML or Haskell). It main claim to fame are (beside garbage collection) goroutines and channels, but I have too little experience with them, so I'd rather concentrate on basic day to day traits of the language. I mean, the small things are the things that annoy us the most, and should a language will be anoying, it will screw them. Additionally, this way we can somehow transmit the "feel" of the language.

So let's start with:

1. multiple assignement

...a la Python:

  x, y := 11, 12
  _, y := 22, 23

As you can see the semicolons are not needed too - gives you a nice Python / F# / Clojure feeling!
If you have mutliple assignament, you get multiple return values for free, as in the following function**:

  func Write(file *File, b []byte)(int, Error)

See? You just specify the returns in parens after the parameters. And that leads us to the next goodie connected to the multiple assignment:

1a. the ok-idiom

it goes like that:

  if ok, x = foobar(y); ok {
    // do sth
    ...
  }

So no more if(foo() == -1)! Instead you can write:

  if nr, err = write(f, buf); err == nil {
    // do sth
    ...
  }  

You can assign and test a value inside of the "if "clause. Additionally the parens can be omitted too with "if" - more Python / F# feeling! Nice, isnt it?

2. named return parameters

We can assign names the return parameters:

  func write(file *File, b []byte)(n int, err Error){
    ...
    
    return
  }

When we name the returns, the compiler will initialize them with defaults (i.e. their zero-values)! We can eithet refer to them inside of the function (!!) or even omit them from the return statement, and then they will be used automatically with the initialized values. One thing less to worry about.

3. maps (and strings)

They are part of the language and not in the library. I wish they'll be that way in C++ too. Come on, D has done that!. Add this to the {} initalization syntax and you can write (almost LISP, Python or Perl style)***:

  var opmap = map[int]string{
    ADD: ”+”,
    SUB: ”-”,
    MUL: ”*”,
    DIV: ”/”,
  }

Well, speaking frankly, the {} initialization is possible in C++ too, alas only as of C++11.

4. defer for destructors

You can define Deferred actions, i.e. actions which are executed on the end of scope only:

  file.Open(”filename.in”)
  defer file.Close()

It's a nice replacement for destructors (see my previous post here). And it looks better that some "using" constructs from  other languages.

5. duck typing

Go has duck typing, but it's not C++ type of template duck typing. You don't have to mention a specific interface (yes, Go has a notion of interfaces!), it suffices to implement them ***:

  type I interface {
    Get() int
    Put(int)
  }

And then you just implement the required functions for a data type (see note ** below), and it will automaticall comply with the interface I:

  type S struct { i int }
  func (p *S) Get() int { return p.i }
  func (p *S) Put(v int) { p.i = v }

like that:

  func f(p I) { p.Put(1) }
  var s S 
  f(&s)

OK, so whats the difference to C++ type duck typing? C++ doesn't care about types: a template with two parameters simply takes two things, and then tests if they have the methods the template code requires:

  template <type T> void foo(T& t)
  {
    if(t.canBark()) t.bark();
  }

How's that different from Go? C++ gets problems with overloading in that context: it sees only a function that takes 1 thing. A totally generic thing! So you cannot define a second template with the same name and a different argument type, because at the definition level there aren't types, only things! That's why there's no range or complete container overloads for SLT algorithms (see H.Sutter's blogpost).

6. generic switch

Just like Groovy, Go has a very flexible switch statement:

  switch c {
    case ’ ’, ’?’, ’&’, ’=’, ’#’, ’+’:   
      return true
    case c < 'a': fallthrough
    case c > 'A':
      return true
    default:
      return false
 }

I mean, ever language needs something like that: case switch for strings and other types! And did you notice that fallthrogh must be stated explicitly? I like that.

7. the go keyword.

I liked the idea of introducing the word "go" as keyword to start a parallel "goroutine":

  int i
  go foobar(i)

I just find it funny :), that's all...

Note:
I admit, I didn't describe the features that make Go to stand out, only a couple of  those which particularly appealed to me. For more info on: function definitions, val notation, control structures, function literals (i.e. lambdas), goroutines, etc please read the book by yourself!

---
* a note aside: as pointed out several times on the web, there's a notable similarity between the logos of Plan 9 and Go. BTW: don't you think they are cute?

** more precise, you'd rather define a function like this:

  func (file *File) Write(b []byte)(int, Error) 

i.e. a function working on the File type, and invoke it like:

  nr, err = f.Write(buf)

But this is the part of the OO stuff so I skipped it in this post.

*** code example from the "Learning Go" book.

2009 Languages Overload

This year (or more to the point, that year, i.e. 2009) was for me a year of languages. Or maybe better, of languages overload! While I'm earning my bacon mainly with C++ (and a bit of Python), this year I had a look at a couple of new languages (adding to my last year's Groovy adventures) like: C# 3.0, Go, Scala, Clojure and even a bit of Haskell. In case of Haskell I'm feeling rather guilty, as I wanted to keep myself busy with Haskell this year but didn't manage more than some superficial reads about monads, and only becaue I needed to explain some Clojure code! Shame!

1. Java

But let me first comment on another language, which is ly dying these days: Java. Is it really dying? Looking at this post by codemonkeyism you'd say so. Why don't we like Java anymore? Let me cite:

Inheritance: outside of frameworks, inheritance is inflexible, leads to tight

coupling and is plain bad. Composition is most often a better choice. As are

mixins and traits

Noisy syntax: Lately there has been the enlightenment that too much noise in a language is a bad thing. Java is especially noisy in closures (anonymous inner classes) and generics.

Null / NPE: Null as the default for object references was a billion dollar mistake. An object should by default need a value. Otherwise NPEs will proliferate through your code. Newer languages prevent nulls or make the null behavior the non default one

List processing: As shown by functional languages, list processing should not be done

in loops. ... Java should have native support for easy list processing, not via the – best we have – constructs in Google Collections.

For me the 2nd problem is the worst, i.e. the noise. It's appalling how much of the Java boilerplate can be thrown away - check this presentation to see how much can be done with Groovy! But each of the new languages does a pretty good job here. Well, to be true, my biggest problem wasn't stated above at all mentionae above - lack of operator overloading! Whatever, the fact is that there's a host of new languages out thre, and the times seem to be more exciting than ever since the 70-ties!

2. Scala

Scala seems to be a language having every single feature from any language known to man. The overall impression was: OK, I know that one from ... One single feature I liked is the solution to the multiple inheritance conundrum (you know, the Deadly Diamond of Death) by linearization of the base classes. Clean, efficient, impressive! From the above list it's solving the Null/NPE, noise and inheritance problems. But the syntax is ML derived! Hate it! if this is a Java replacement, why cannot we stay in the old good C-lands? Another problem with Scala is poor tool support: I wasn't able to get the Eclipse plugin running, despite applying various workarounds found on Scala's homepage and upgrades of both the platform and the plugin. Even Martin Odersky (Scala's creator) is using Emacs for work!

On the other side, I think Groovy solves the list processing more elegantly, and it's DSL capabilites are more convincing too! (example to come)

3. Clojure

I like Clojure! I don't know why. It's not typesafe, has Lisp-y syntax and very complicated mechanism for integration of Java class libraries, but it is somehow elegant and minimalistic. It includes mutithreading primitives in the language definition and it tries to achieve good performance while staying immutable!

As I watched this presentation by Rich Hickey I noticed one important thing: he's an architect who was facing design problems in complex real life systems* (somehow like me, although I must admit that he's been exposed to more complexity than me) an tried to find a solution. And he really knows his stuff - all the conventional wisdom of software architecture! And Clojure (and Clojure's features) is an answer to these problems: it takes from LISP what seems suitable and isn't afraid to change it** otherwise.

Contrast this with Scala - sometimes feeling like an academic exercise in trying implementing all the features known to man in a single programming language just to show that it can be done (caveat: totally subjective opinion here). Maybe this pragmatic legacy is one of reasons why I like Clojure much more then Scala.

4. F# (and C#)

C# seems to be evolving very rapidly. From the ugly duckling it was a couple of years ago, it developed a respectable language with a decent amount of innovation. It has good lambda function support and the LINQ concept is rather interesting. I was surprised!

F# in its turn seems to be syntax-wise another ML derived langage like Scala, but it's not so overloaded with features. Sorry, I'm still not done with the free F# book...

Some (for example Scala Lift's creator here) say that it could be the single one of functional languages to success in the mainstream!

5. Go-lang

I didn't like it that much despite of its heritage. The obligatory, one and only true formatting rules, lack of subclassing... But on the other side, there is a CSP implementation on the language level! And as another programmer, who actually tried it out, stated here, it's much like writing in Python, only without its excruciating slowness. So maybe I should switch from Python to Go? Google Application Engine supports it now!

Update: in the meanwhile I managed to have a look at Go!

6. Summary

Warning: You see, it's not the comprehensive comparision I wanted to write back in 2009/10, but before I ditch the project altogether, I'd rather write this stub and extend it when I find some time. But the summary is already complete now, so... ---->

As I said above, I'd use Scala as a "better Java" as to avoid Java verbosity, lack of operator overloading and multiple inheritance. I'd use Closure for the joy of if (pun intended), I'd like some of my clients to want me to use Go, but wouldn't propose it myself, and I probably won't use C# unless I switch to .NET which is rather unlikely. On the other side, I might install F# on my PC - just to play with it a little.

--
* according to InfoQ "...Rich has worked on scheduling systems, broadcast automation, audio analysis and fingerprinting, database design, yield management, exit poll systems, and machine listening."

** e.g. even the venerable parentheses!

Exegi Monumentum...

"Exegi monumentum aeris perennis"* - I don't know why but this line is always coming to my mind when I'm thinking about my father, who passed away more than 2 years ago. Just because he was fond of classical studies and Latin?

He also cherished that other lines of poetry, in a language that you can't possibly know, but which, as I can assure you, are work of a genius (I cite form memory):

"Wsrod takich pol przed laty, nad brzegiem ruczaju,
na pagorku niewiekim, we brzozowym gaju,
stal dwor szlachecki, z drewna, lecz podmurowany,
swiecly sie z daleka jego biale sciany,
tym bielsze, ze odbite od ciemnej zieleni,
topoli, co go strzegly od wiatrow jesieni."

You're right, that's a single sentence. And he could recite one after another in the endless flow of the language. Yes, you are right again, this is a hommage to my late father, which I'm writing 2 years too late. The first thing I'll always associate with him will be the classical poetry. The another one, linked via the above phrase of Horace, is a story of an interview and things which it revealed to me in retrospect.

It was my school appointment to interview someone and I choose to interview my father. I remember just a single question I asked: what do you want to be remembered for? The answer was somehow unexpected to me: he cited the line of  Horace, and said: I want to be remembered for the things I accomplish. And he did, he was working in local political bodies and was involved in building roads and water supply lines in our rural neighbourhood.

So when it came to finding a vocation, I wanted to build things! Not maths, physics, literature or music (things I was interested in), but engineering!

As for us in life there are 2 things which are worth of pursuing: for yourself, trying to understand the great scheme of things in that world (for practically minded, if you are more ambitious it's the universe then). But secondly, you owe it to the others, those before you and those to come after you, to keep the world running smoothly, and build new smootly running things to replace old ones.

I think, that's my father's heritage. And that's why I cannot be a geek - because I grew up listening to poetry, looking at nature of the rural coutryside and experiencing very practical achievements in very real world.

--
* fom Horace, translation mine: "I build a monument [to stay] for perennial ages"

Agile Rant Update

After you've read my Agile rant you may have though: "just another old-fashioned hacker who just doesn't get it...". Fair enough, I'm myself not that sure if that what I'm saying isn't just result of lack of experience with Agile? Maybe with even more exposure all my reservations would vanish?

So I'm happy to find out that there are other people thinking roughly along my lines. For example here: Agile Hokum, in DDJ reader mail. He (the reader)says exaclty what I said:

But the "TDD corrupted by writing the tests after coding" is about as extreme as the Taliban. Testing is good. Write them before, during, after, much after, etc., all have their place.

and doubts usefulness pair programming as well. The standard TDD answer of the expert goes than like that:

I agree that tests written at anytime will generally have value. However, TDD was not designed as a way of validating code — plain unit testing will do that. TDD is first and foremost a design practice. And so doing TDD by writing the tests after the code is simply a misunderstanding of what you’re actually doing.

Well, that opinon is already dealt with in my Agile rant. But taking the simplistic road I'd just say that's the way it is handled in agile projects: not as a design technique but rather as a testing one. OK, here seems to be some confusion on the term itself: it's either Test Driven Development or Design...

On the other side the author (i.e. the reader) openly admits that he's not an Agile practitioner, so that opinion doesn't give any earnest support for my criticism?.

But look what an ex Googler says here:

This is not to say that all unit testing is bad--of course not. The dispatch logic in Guice Servlet and Sitebricks benefit from rigorous, modular unit tests. If you have ever used Gmail, Blogger, Google Apps, AdWords or Google Wave (all use Guice Servlet to dispatch requests) you have seen the benefits of this rigor first-hand. But take it from me, we could have achieved the same level of confidence with a few well written unit tests and a battery of integration tests. And we'd have been in a much better position to improve the framework and add features quickly.

That strikes a chord with me, because it's exactly the way I tested my last system - a lot of integration and pre-integration tests, and a couple of unit tests for classes which couldn't be easily tested thorougly that way. Wouldn't that be allowed at your company? Because this isn't Agile?