Segfault in Ruby
Note: the following works with C-based ruby, not JRuby or IronRuby, obviously.
This is a sight most rubyists will fear: the segmentation fault. You’re running your tests quite innocently, or your web server is doing it’s job, until BOOM !
[BUG] Segmentation fault
What just happened ?
A segfault means your program tries to play fast and loose with memory it hasn’t been allocated. The operating system says ‘hey you!’. When this occurs on a *nix, the process receives a signal, SIGSEGV. The program crashes, and in so doing leaves a core dump, which is a recording of the state of the program at the time of crash.
Ruby then traps the corresponding signal.
You’ll find corresponding code in signal.c of the ruby source code:
install_sighandler(SIGSEGV, sigsegv);
and the sigsegv function is:
#ifdef SIGSEGV
static RETSIGTYPE sigsegv _((int));
static RETSIGTYPE
sigsegv(sig)
int sig;
{
#if defined(HAVE_NATIVETHREAD) && defined(HAVE_NATIVETHREAD_KILL)
if (!is_ruby_native_thread() && !rb_trap_accept_nativethreads[sig]) {
sigsend_to_ruby_thread(sig);
return;
}
#endif
rb_gc_unstress();
rb_bug("Segmentation fault");
}
#endif
The rb_bug at the bottom is responsible for the message you see appearing when a segmentation fault happens.
That’s all well, you’ll say, but how to I solve this ?
First off, you have to determine where the issue came from. There’s where the core dump can help you, by telling you if the issue happened in ruby itself, or in its binding to another component, like a database or something similar.
(more…)
FOSDEM 2010: all was well
This weekend we had our 10th edition of FOSDEM. Fosdem is the Free Open Source Developers European Meeting. It’s the second year that I’m part of the staff – my reasons to join the team was that since I’m using a lot of open source, but contributing precious little (working on it), I might as well give something back in another way. Since then I found another reason to enjoy working on FOSDEM: it’s amazing to bring about such a mammoth event with just a dozen of people and a larger group of volunteers.
Since FOSDEM is entirely free and doesn’t require people to register, it’s always difficult to estimate the attendance. Judging from the numbers of t-shirts and the booklets, and the constant throngs of geeks in the hallways, the general impression is that we had even more participants than last year. To the point that we start wondering if we’re not going to grow too large.
The organization was a success. Kudos to the whole team for doing a good job.
Sponsoring and donations were crisis-insensitive. The network was up on friday night (respect to Gerry, Jerome, Peter, and all who made it happen), with a glass fiber gigabit uplink. During the conference the geeks didn’t even use 10% of the bandwidth. In one of the hacker rooms there was a sign ‘please use more bandwidth’. The devrooms were mostly packed, and the main tracks were (I think) interesting. It’s not always easy to get brainiacs who can speak in front of an audience, but I think we hit the spot most of the time.
Where last year I had to run around like a headless chicken, this year there were plenty of opportunities to sit down for 20 minutes at a time ! Which meant I got out of it feeling marginally less exhausted than last year.
I think we can say that the organization has now reached a nice plateau, and everything was ticking along very smoothly. The only danger is to grow complacent – it’s never a good idea to let your guard down.
Heart-warming: to have faithful volunteers who help us until the bitter (or should I say dirty) end. To have a great atmosphere, and to get heartfelt thanks from participants. If you’ve got any feedback of your own, tips you’d like to share, let us know.
Bye bye mac
For about 2 years I’ve worked on a Macbook Pro. It’s been a mostly pleasant experience – smooth graphical interface, more than adequate hardware – it took a while getting used to, but it worked out OK.
Still, I find myself turning back to Linux for development.
Mess
I’m not the most organized person in real life, but I can be fairly anal about my file organization. And I find it quite an effort to keep my Mac’s file structure clean and simple.
First, there is Apple’s own directory structure – apparently they found it necessary to differ from the BSD they’re based on, and use a list of non-standard capitalized (!) directories (Libraries, System etc – have a look at Applications for pete’s sake).
In my work I use a fair number of open source tools. The easiest way to get those on a mac is using macports. Macports installs things in /opt/local by default, so there’s a few things lying around in their own directory structure there.
The macports people do good work, but it’s difficult to keep up with releases, so often you need a newer version of a tool, or you need an extra library that hasn’t been packaged yet. So you compile. If you’re not careful, the compiled items are then installed in the usual linux directory structure (/usr, /usr/lib etc).
Result: something that works, but it can become a disorganized mess, which chafes a bit.
(and don’t get me started on Mac’s very own dynamic libraries and executables)
Tools
when I work, I’m mostly using terminals and the command line. Vi is my editor of choice (good vim rails plugins here). So all the nice graphical effects and applications requiring a mouse don’t have much added value.
Friends have introduced me to a great window manager on Linux, coincidentally called Awesome. This is a tiled window manager – which means that most windows don’t float, but are tiled, and make full use of the screen real estate. There are by default 10 desktops, allowing a good organization of windows. Navigation happens through key shortcuts. Shortcut keys, default applications, the whole interface can be customized using Lua. Now tell me that isn’t awesome.
Linux for the desktop
It used to be a pain in the neck to have Linux be completely functional, especially on laptops. I remember poring over hardware manuals looking for chipsets, and endless trawling through forums to get X to work properly. Nowadays installing an ubuntu or a debian is mostly inserting a disk and clicking through an install.
Because you see, it’s not because I can manually partition, hand-compile kernels and libraries, fiddle about with settings, that I want to spend time doing this for my desktop, per se. We’ve all got better things to do. Zack the Mac was a temporary solution to this issue.
Apple
Fourth (minor) reason to go back: well, Apple. They have the hardware, they have the software, they make me pay. It feels like being submissive to the fantastic marketing machine Steve Jobs set up.
I like the mac hardware, and Mac OS X is fine for casual use (like watching movies, email, blogging), and of course for iPhone development, so it’s not a definite parting. Might make my MBP a dual boot (I’m told boot camp makes this very easy). Let’s see how this goes !
26C3
I’m not quite sure how I ended up at 26C3, but I had a blast.
From what I gather, the Chaos Communication Congresses are gathering of geeks and utopians (or both), around security, privacy and hacking. And LEDs.
We arrived the night before the start of the conference. We were lucky to have our places in advance, because when we went to retrieve our bracelets, people were queuing up to get their places.
The location of the 26C3 (and a few previous ones) is fantastic. The Berlin Congress Center is a graceful example of 70 architecture of the 2001 welcome to the future category. It’s basically a bloc containing a cylindrical structure – the outside edges are the corridors, the inside disks are rooms. Saal1 (under the cupula) in particular is phenomenal, but the rest of the building has lots of charm too.
The principle is that groups and projects book a table (or two), and gather round that table to sit, and hack, or misc. I ended up at the Debian table (‘debianist by association’), thanks to the friends I was traveling with. There were tables with people having brought really old hardware, tables with robot arms, and everywhere laptops.
At 26C3 they set up all kinds of networks. The building is properly wired, and there were a few wifi network that worked reasonably well. Then there was the DECT radio network, which means everyone was walking around with your average domestic chordless phone (DECT radio for those in the know). They even set up a GSM network which didn’t work too consistently, but was way cool nonetheless: instead of vodaphone et al. you had an in-house network which even worked for normal domestic calls !
The talks were streamed live. I didn’t attend that many talks in person, as the rooms were really packed. Besides, knowing that the conference recordings would be available later also made it less of an incentive to try and pile in. The talks I did attend/listen to were fascinating.
One talk I attended was about stylometry, or how you can in certain situation detect who’s the author of a text by the word choice, grammar, etc. Which obviously means danger for whistle-blowers publishing anonymously against an abusive employer or an oppressive regime. The author was trying to ‘attack’ those techniques, by trying pastiche or obfuscation. Another talk was about intelligence support systems, and their use by all kinds of organization. I also followed a talk about attacks on PKI, which is interesting since my current work is all about PKI.
The ground floor was catering mostly, and the lower floor was the hardware hackers floor. The catering floor was visited many times to get a dose of Club-Mate. Mate is a naturally caffeinated kind of tea leaf from South-America. Club-Mate is a soda version of that, and quite tasty and effective, as energy drinks go.
Then there were all the cool toys ! You could buy kits of electronic circuits to assemble yourself. I bought and assembled the TV-B-Gone kit to switch off tv’s, which worked, and a dotblox64, which lots of LEDs, which doesn’t yet (because of slightly shoddy solderwork). There was a group making helicopters, and a group building and programming LEGO robots to fight against eachother. Geek heaven, or what.
I also had a go at lockpicking, though I must admit that I miserably failed at that, being quite clumsy (the instructions in german might not have helped). The stories of the instructor (from lockpicking.org and the lockpicking club of Berlin) were interesting. He explained about how locks usually worked, about different kinds, and the pleasure and effort to figure it out. He also bragged a little about his exploits, of course: seems he has a master key of the Berlin underground, and the Berlin public toilets.
The general vibe was one of love for freedom. Lots of subculture represented, though obviously the overarching one was geekiness. No judgments, no rules, things were built for fun, not necessity. A fairly mixed audience, a slightly subversive but enthousiastic spirit. I had a good time, and will enjoy watching some of the remaining talks at home.
Pretty docs for rubygems
Tip I got through my colleague Bart Duchesne:
to have nicer templates for the rubygem documentation, you can use templates.
Mislav’s Hanna templates are pretty decent (way better than the default ones anyway) – there are other options if you look around.
Howto (updated from this site):
gem install hanna- follow the instructions given here – best to put following line in your .gemrc
rdoc: --inline-source --line-numbers --format=html --template=hanna - to regenerate all rdoc
sudo gem rdoc --all --no-ri - install the sinatra-rubygems (after having installed sinatra – gem install sinatra – if you haven’t got it already)
git clone git://github.com/jseifer/sinatra-rubygems.git
It’s a web application (duh) so keep this in mind in choosing where you want to clone it - point your apache+passenger (replace by suitable web server) to
directory/sinatra-rubygems/public
(and give it its own port, of course) - bookmark the link in the toolbar of your favourite browser
- Update: rather than using apache and sinatra, you could also install bdoc
sudo gem install bdoc
- no extra web servers needed ! and build the necessary index typing
bdoc
this will start up the index in the default browser, and the UI is even nicer
(thanks to Josh Kim for the tip)
doesn’t seem to work under ubuntu, I’ll see if I can fix it
You can add a cherry on top by also doing the same for your ruby, by fooling your system into thinking it’s also a gem.
They say laziness is a virtue in programmers: voila, you have your ruby documentation just a click away, and offline too.
Learning iPhone development
This summer I’ve had the mixed pleasure to get acquainted with the iPhone development platform. I have an iPhone, I enjoy using it, it seemed like the logical next step. I’ll share some tips so that if you feel like diving into it, you’ll know where to start, and also what you’re getting into.
- some preliminary objective-C knowledge is useful. The Apple doc gets you up to speed. Objective-C is an object-oriented language, and if you’ve done a strongly typed OO language like Java it shouldn’t be too hard. Some attention should be paid to memory management – if you’ve got some C in your past, that helps.
- Then, get a book. The Apple documentation is boring, it’s a reference, but not a tutorial. I used “Beginning iPhone Development” from Apress. This is pretty good: very hands-on, every concept is illustrated with a small project, so you can test yourself.
- Just so you know, you need to install Xcode to develop for iPhone, in other words, you need a mac. Really ? Really. The development tools are quite good, but there’s no way around the Apple universe.
- Plan for your first real project as soon as possible. You’ll need a decent app in your portfolio if you want to start developing commercially anyway. It’s the best way to learn.
- If you want to release your application to the AppStore, you need to subscribe to the iPhone Developer Program, which, the last time I looked, cost $99. Wait, scrap that, if you want to install your app onto your own iPhone you paid for yourself with your own hard-won money, you need to subscribe to the Developer Program. The iPhone will only admit executables which have been signed by Apple with what’s called a ‘provisioning profile’. That’s to keep people from circumventing the AppStore.
Also, the best code samples, download and docs are only available to people who are registered. - Be aware of the rules and regulations (PDF). Apple reserves the right to reject your application.
Don’t get me wrong, it’s relatively fun to develop for an iPhone. But it’s vendor lock-in raised to a whole new level. </rant> Unless there’s suddenly an enormous demand for iPhone applications, I’m not sure I’ll be pushing that part of my skills (after I finish developing my current application, to which I agreed). We’ll see.
The Real-Time web
Like all of the over-connected, I’ve been intrigued by the hype around the so-called realtime web, so i’ve been looking around and reading up. Today, I had an opportunity to bring it all together in a short presentation.
The main points I was trying to make:
- nothing new under the sun, technologically: HTTP callbacks, and then ajax and js push for the webby stuff
- taking a step back, and having a nuanced view, is as always a good idea
The structure is partly inspired by Jeff Lindsay’s talk about webhooks at Pivotal Labs. I gave 2 demo’s. The first is the one described by Ilya Grigorik in his post about pubsubhubbub, where I used the watercoolr site itself and postbin. The second was an illustration about how the magic of Google Wave can be reproduced using ajax and juggernaut (though I’m sure their solution has more complexity, since they have a much, much higher load).
The last image (the house) is to talk about a nice example of the real-time web (internet of things, yay): the Pachube application now has triggers. Pachube acts as a hub for sensor information: so that means you can put triggers on your sensor data. As in ‘my house is colder than 10 degrees, notify me’.
Service announcement: I’m going to move this blog to another hosting very soon, under a new domain name (jabberwocky.eu). Well, I’ll post here to say it, anyway.
I survived a Rails Rumble
“Why do I do these things to myself ?” is a question that came to mind this weekend, during the Rails Rumble. The principle of the weekend is simple: you develop an app in 48 hours, from midnight GMT on friday to midnight GMT on sunday.
Hendrik, Yoni and I came together at the office i share to have a go (Tom helped us for a few hours). Hendrik did the front-end integration, Yoni the design and CSS, Tom is a Rails developer. We’d brainstormed beforehand and came up with a nice and simple concept: Same Same, an application that allows you to create before-after stories with pictures. Loads of potential for storytelling (before-after haircut, after 1 beer, 2 beers, 3 beers, before-after food fight, the stages of pregnancy) .
Well, it took caffeine, chocolate, pizza, blood, sweat and tears, but we made it, goddammit.
Lessons learned:
- I do my best refactoring in my sleep, or in the shower. None of which were available in any great quantities during the weekend
- Simple is better: in this case, adding more functionality made the application more difficult to understand. We probably should throw out the voting mechanism, and add a big and obvious ‘next’ button.
- Lots of little technical things, like Rails templates I hadn’t used before, jQuery live validation, uploadify, …
What I’d do differently, if i did it again:
- more than 1 (full-time) developer is necessary. You need a pair, or at least someone to do sanity checks – by hour 25 you’re starting to lose your edge.
- Tests: i threw out testing thinking I’d gain time, but I didn’t – test sets immediately show breakages, and these occur even in the most sane situations, which this wasn’t.
- sleep more, like 6 hours in the middle – i slept 3. What you lose in time, you gain in focus. When i woke up on monday, i knew how to solve the app’s most obvious bugs in about 3 code lines … frustrating
No patching is allowed after the 48 hours …
I liked working with Hendrik and Yoni, and I think we made a good team, overall. We should have recorded our conversations from hour 45, it got fairly surreal. It was a good experience, one that, I think, made me a better developer. I’m intending to pick up Same Same later, rework it a little bit and put it online in a proper manner.
3 comments