Code Quality In Open and Closed Source Kernels

Diomidis Spinellis writes "Earlier today I presented at the 30th International Conference on Software Engineering a research paper comparing the code quality of Linux, Windows (its research kernel distribution), OpenSolaris, and FreeBSD. For the comparison I parsed multiple configurations of these systems (more than ten million lines) and stored the results in four databases, where I could run SQL queries on them. This amounted to 8GB of data, 160 million records. (I've made the databases and the SQL queries available online.) The areas I examined were file organization, code structure, code style, preprocessing, and data organization. To my surprise there was no clear winner or loser, but there were interesting differences in specific areas. As the summary concludes: '..the structure and internal quality attributes of a working, non-trivial software artifact will represent first and foremost the engineering requirements of its construction, with the influence of process being marginal, if any.'"

Comments

Is it just me?

[Abreu]

Or the summary is completely incomprehensible?

Of course, I could try to RTFA, but hey, this is Slashdot, after all...

Re:Is it just me?

[Diomidis Spinellis]

It's not a very good summary, but the paper is well-written, which is interesting considering that the author is the one who submitted the summary to Slashdot. I suspect that he assumes we have more familiarity with the subject than we actually do. In my submission I did not include the last sentence with the "summary", which, I agree, is completely incomprehensible in the form it appears.

Re:Is it just me?

[utopianfiat]

Well, it's the second link. At any rate, the highlights of the data are that for the most part the kernels are tied in the important material, except:

% style conforming lines: FBSD:77.27 LIN:77.96 SOLARIS:84.32 WIN:33.30
% style conforming typedef identifiers: FBSD:57.1 LIN:59.2 SOLARIS:86.9 WIN:100.0
% style conforming aggregate tags: FBSD:0.0 LIN:0.0 SOLARIS:20.7 WIN:98.2

(I'm far too lazy to clean up the rest)

% of variable declarations with global scope 0.36 0.19 1.02 1.86
% of variable operands with global scope 3.3 0.5 1.3 2.3
% of identifiers with wrongly global scope 0.28 0.17 1.51 3.53

Not that surprising

[abigor]

Final line in the paper: "Therefore, the most we can read from the overall balance of marks is that open source development approaches do not produce software of markedly higher quality than proprietary software development."

Interesting, but not shocking for those who have worked with disciplined commercial teams. I wonder what the results would be in less critical areas than the kernel, say certain types of applications.

Re:Not that surprising

[Diomidis Spinellis]

I don't think that my results can support us in making arguments regarding 'slightly' higher quality, or 'exactly the same quality'. My figures are based on possibly interdependent, unweighted, and unvalidated metrics. Therefore they only allow us to make conclusions involving large differences.

The 99% Solution

[SuperKendall]

So while looking at the data collected, I had to wonder if some of the conclusions reached were not something of a matter of weighting - I saw some things pretty troubling about the WRK. Among the top of my list was a 99.8% global function count!!!

This would explain some things like lower LOC count - after all, if you just have a bunch of global functions there's no need for a lot of API wrapping, you just call away.

I do hate to lean on LOC as any kind of metric but - even besides that, the far lower count of Windows made me wonder how much there, is there. Is the Windows kernel so much tighter or is it just doing less? That one metric would seem to make further conclusions hard to reach since it's such a different style.

Also, on a side note I would say another conclusion you could reach is that open source would tend to be more readable, with the WRK having a 33.30% adherence to code style and the others being 77-83%. That meshes with my experience working on corporate code, where over time coding styles change on more of a whim whereas in an open source project, it's more important to keep a common look to the code for maintainability. (That's important for corporate code too - it's just that there's usually no-one assigned to care about that).

Re:Closed Source?

[zeromorph]

The WRK is under the Microsoft Windows Research Kernel Source Code License. I'm not sure that this license conforms with anyones definition of open source, but it's reasonably free for reasearch.

But PP addresses a crucial point, if something really is closed source there is no reviewable way to compare and present this code. So if the WRK would be total crap they could always say: yes that's only the WRK, not the real kernel.

Only statements about open source code are directly verifiable/falsifiable. One of the reasons, why the FOSS approach is superior from a scientific as well as technical point of view.

An interesting point..

[SixDimensionalArray]

I haven't seen anybody else comment on the fact that the statement that the quality of the code had more to do with the engineering than the process through which the code was developed is quite interesting.

From my personal experiences, it typically seems code is written to solve a specific need. Said another way, in the pursuit of solving a given problem, whatever engineering is required to solve the problem must be accomplished - if existing solutions to problems can be recognized, they can be used (for example, Gang of Four/GOF patterns), otherwise, the problem must have a new solution engineered.

Seeing as how there are teams successfully developing projects (with both good, and bad code quality) using traditional OO/UML modeling, the software development life-cycle, capability maturity model, scrum, agile, XP/pair programming, and a myriad of other methods, it would seem to be that what the author is saying is, it didn't necessarily matter which method was used, it was how the solution was actually built (the.. robustness of the engineering) that mattered.

Further clarification on the difference between engineering and "process" would strengthen this paper.

I went to a Microsoft user group event some time ago - and the presenter described what they believed the process of development of code quality looked like. They suggested the progression of code quality was something like:
crap -> slightly less crappy -> decent quality -> elegant code.

Sometimes, your first solution at a given problem is elegant.. sometimes, it's just crap.

Anyways, just my two cents. Maybe two cents too many.. ;)

SixD

"Code quality" is bunk

[mlwmohawk]

Sorry, I've been in the business for over 25 years and had to hear one pin head after another spout about code quality or productivity. Its all subjective at best.

The worst looking piece of spaghetti code could have fewer bugs, be more efficient, and be easier to maintain than the most modular object oriented code.

What is the "real" measure of quality or productivity? Is it LOC? No. Is it overall structure? no. Is it the number of "globals?" maybe not.

The only real measure of code is the pure and simple darwinian test of survival. If it lasts and works, its good code. If it is constantly being rewritten or is tossed, it is bad code.

I currently HATE (with a passion) the current interpretation of the bridge design pattern so popular these days. Yea, it means well, but it fails in implementation by making implementation harder and increasing the LOC benchmark. The core idea is correct, but it has been taken to absurd levels.

I have code that is over 15 years old, almost untouched, and still being used in programs today. Is it pretty? Not always. Is it "object oriented" conceptually, yes, but not necessarily. Think the "fopen,"fread," file operations. Conceptually, the FILE pointer is an object, but it is a pure C convention.

In summation:
Code that works -- good.
Code that does not -- bad.