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eXtreme Programming (XP) in OSS projects?
ivi asks: "I first bumped into the XP approach to system development, some years ago, on Dr Dobbs' now-defunct Seminar-On-Demand site TechNetCast. XP has some short, simple rules for growing software from Users' Stories, eg, with programmers working in pairs,
showing prototypes to Users "early & often" et al. Download this XP site (under 400KB, zipped) for more.
So, who's used or using XP, does it work for OSS projects & what have your experiences been with it, so far?"
We tried XP approaches in my college programming classes. More often than not, it caused my partners and I to claw each others' eyes out, and generally despise your partner for the remainder of the project.
What worked MUCH better was designing the framework from the beginning, outlining how the different functions/processes/data structures etc. would have to communicate with each other, then splitting the programming tasks up.
After every one made progress, we'd recombine, work out bugs, etc.
Much more organic and realistic than the XP approach, which always seemed very articifical and limited.
I remember reading an article on O'Reilly about XP and Open Source .. go dig it up..
:-).
I don't have any experience with XP in writing open source projects, but I sure see a lot of projects that can benefit from it!!
I would love to see more software with comprehensive tests. It's very satisfying when you hack a minor change into a program and all the tests still pass. Then you can send the patch off to the author knowing it won't break anything (well, at least it won't break any of the tests
In this vein, I believe test-driven development (i.e., write tests, write any code that passes the test, then refactor to clean up the mess) is the most amazing gift from whoever the programming gods are. I'm glad XP has (re-)discovered it.
It forces much simpler, cleaner interfaces, and complete unit tests. There have been several times when I've wished that a particular open source program was split into many small objects that I could mix and match (i.e., I love this package BUT I need to replace the code that saves files to disk with code that saves files to a database..etc).
With TDD your design splits into many small simple classes. I think this would be great for OSS projects. A good example of a well-factored library (off the top of my head) is Mime::Tools for Perl.
Too many OSS developers think "I used Python, I must be doing object-oriented programming" or something along those lines.
Some other aspects of XP such as continuous integration seem useful.
Another thing about XP techniques (especially test-driven development again), is you can code in small bite-size chunks and not leave the code in a broken state. I think this is great for projects you might have "on the side". You can work an hour or two and your code will always be working and passing tests, none of these "egg-juggling" 10-hour coding marathons. You know what I mean, when you change something and it ripples to 20 files and you keep all the things you need to do in your head and you go half-insane running from file to file.
Pair programming, user stories, "Customers", etc., seems less useful.
But yeah test-driven development is worth trying, at least.
My initial impression of XP (I haven't tried it but had it explained to me) is that it takes a lot of the fun and programmer-as-artist aspect out of software development. Also it is good for making a larger number of so-so programmers as productive as a few really good programmers.
However, most OSS projects seem to be labors of love by groups of individuals working together in their spare time. I would bet most of the largest contributors to OSS projects are very good programmers who don't need to be "managed" to the extent that XP does. I don't see how many of the XP ideas could be applied when none of the developers are in the same room on a regular basis (or even available to meet on-line at one time), their time commitments are unpredictable, and in many cases have big egos and work on what they feel like, not what the customers ask for... After all, programmers have day jobs that are like that!
Having participated in a number of OSS projects, and even led/maintained a few, I can't see how Extreme Programming can help - the model is clearly better suited for in-house programming than distributed programming.
Many of the same techniques are used in OSS projects though. "Release early, release often" is almost biblical to people from what can soon be called a Linux-background, and another rule is "No functionality is added early.", which fits my personal design philosophy pretty well, and a lot of OSS projects: I can't remember the last time I added functionality to a program.
If your open source project is being developed by a team of people all sitting in the same building, directed by a customer who's paying for the software and who accepts XP, then yes, XP should work just fine.
If your open source project is being developed by volunteers all over the world in different time zones, then forget it. Getting XP to work in that situation is probably possible, but difficult and probably expensive.
But if you, like so many others, are using XP as an excuse for shoddy development practices (the "look, we don't need to do requirements analysis or design or documentation because we're using XP" syndrome), then by all means go ahead. It'll work just fine as an excuse.
So let's get to the details. I understand XP pretty darn well. We deployed it successfully at my shop, making all the classic mistakes (and some of our own) on the way. We finally got everything right, and once we did, it worked really well.
I'm going to assume that "open source project" means a project with volunteers all over the world (or all over the country), and no paying customer.
Problem 1: The customer role
The "customer" in XP is a person who represents the users and can make decisions regarding what to implement and when. It's not necessarily a paying customer or an outside person.
The customer is a key person in XP. If you don't have a customer, you can't do XP and if the developers don't do what the customer requires, you can't do XP.
Developers don't make good customers. They're too involved in the technical side of the project and rarely prioritize well. You really need an outsider who is focused only on the end result.
Developers have to listen to the customer. The customer decides what gets done. The developers have no choice in the matter. They can tell the customer how much it will cost to get something done, but in the end they have to do what the customer wants.
Do you have a customer on your project? Will your volunteer developers do what the customer wants? If either answer is no, forget about XP.
Problem 2: Pair programming
Pair programming gets left out of a lot of XP projects. That's unfortunate, because pair programming is a key ingredient of XP. Without it, the process hobbles along.
There are lots of reasons why people give up on pair programming. The poster mentions one: not leaving that big programmer ego at home (it's just programming, not personal). There are others.
What you need to understand is that pair programming is how knowledge and skills are communicated in an XP project. Pair programming compensates for lack of formal design and documentation. Pair programming cuts down on both trivial and serious bugs (the brain not writing the code is usually thinking about the big picture). We found that code written by pairs was consistently better by all subjective and objective criteria we used.
Can you do pair programming in your open source project? If your developers are all in one place and work at the same time, then it's easy. But if they're not, you'll find it very difficult. Instant messaging or even speakerphones don't really help much. And remember, pairs are supposed to be unstable. If you always work with the same person, you'll lose a lot of the benefits of pair programming.
Problem 3: Communication
XP developers tend to be pretty chatty, in my experience. At our shop, verbal communication was a very important component, and to ensure that it was easy, we all worked in the same room (no partitions at all).
How easy is it for your developers to communicate? Instant messaging helps, but isn't all that good since you can't count on instant feedback. A phone works pretty well, but it should be a speakerphone (a headset is OK, but less effective). Are your developers working at the same time? If they're not, how are they going to talk to each other while they work?
In conclusion . . .
T