Muli Ben-Yehuda's journal

I’m writing this while sitting in a colloqium talk at the IBM Haifa Research Lab auditorium, where I work. Shoshannah Forbes, of linux-il fame, and Gidi Aharonivich, who’s blind from birth, are giving a talk on website and otherwise accessibility. As far as I’m personally concerned, they’re preaching to the converted. However, I never write websites and shy away from writing any sort of non textual user interface, so anything I write is (not?) accessible by definition.

Later today I have the second algorithmics class, which I’m looking forward to (see last week’s entry).

LOL, Gidi just mentioned that many sites that specifically cater to the blind are actualy not accessible to the blind!

Good talk, too bad my laptop’s battery died in the middle. *grumble*.

Shachar Shemesh, Hamakor board member and all around good guy, has a new blog on pcplus. Sadly, it’s in Hebrew, but still, good stuff there.

Gilad Ben-Yossef, another Hamakor board member, used to have a very enjoyable blog, but no longer updates it. Shame.

On Monday afternoon, I gave the from python import lecture talk to Haifux. About 20 people showed up, which was considerably more than I expected, considering we’re in the middle of the Technion’s exam season. The talk went rather well, if I may say so myself. I made the usual mistakes of talking to the more knowledgable subset of the audience, but I also made sure to explain even things that seem obvious to me and that subset, because they weren’t necessarily obvious to the rest of the audience.

Giving this talk was harder than usual, because I’m no python expert. I gave it for the first time a year and a half ago, in order to have an excuse for learning python, and yesterday I gave it again in preperation for moshez‘s advanced python talk at the next club meeting, but I’m not a python guru for any stretch of the imagination. We have moshez for that. During the lecture there were several questions I had to answer with “I don’t know”, but all of them were answerable with 10 seconds in front of the python interpreter.

All in all, an enjoyable evening, even though I was very tired. Next semester I’ll be studying Algorithms on Monday evenings, so no Haifux meetings for me after September. I’ll miss the club, the clubbers, and the talks.

On Sunday afternoon I registerd for my fourth class for the upcoming winter semester at the Open University. Previously I registered for Infi I, Compilation, Algorithms and on Sunday I registered for Mathematical Logic, an advanced math class. I studied logic in the Technion, but never quite got the hang of it. I have since learned many things and expanded my (mathematical) horizons, and I’m hoping this time to be rather more educational.

On Sunday evening, Orna, my mother, my little sister and myself went to hear the Haifa Symphony Orchestra perform Beethoven’s 9th Symphony. I was under the impression that it will be a short concert, composed solely of the 9th, which was a blessing as both Orna and I were after long days at work. As it turns out that there were two other compositions on the menu. The concert started with Yosef Tal’s 1st Symphony, which Orna enjoyed, but I found rather simplistic (“plink”, said the violins, over and over again), and Brahm’s Raphsody for Alt, which we both found rather soothing, to the point of falling asleep. By the time the (long!) break finished and the orchestra started playing the 9th, Orna and I were both ready to fall asleep in our seats. The 9th was great, as usual, and I managed to wake up a little towards the end, but all in all, next time I’m sleeping before a concert!

ladypine[0] bought me Neil Stephenson’s Quicksilver[1][2][3] and Greg Eagan’s Diaspora[4].

[0] I *heart* ladypine.
[1] *droool*
[2] Have I mentioned Cryptonomicon is likely my favorite book? well, maybe second to Stephen King’s IT.
[3] not yet published…
[4] I hope it gets here in time for the flight to OLS. .ca is a long way off.

Here’s what I wrote to Haifux, CC’d to linux-il:

Updated slides [for my python talk] are now available at http://www.mulix.org/lectures/python_intro_2/python_intro_2.pdf. LaTeX source available at http://www.mulix.org/lectures/python_intro_2/python_intro_2.tex.

Note that the slides are even less descriptive than my usual non-descriptive style this time. They are composed almost completely of code snippets which illustrate python in its myriad forms, to be discussed and elaborated upon during the talk. For something readable, I recommend the excellent python tutorial at http://www.python.org/doc/current/tut/tut.html, which the slides are based on.

100 in probability. Now that’s a nice birthday present!

Exam in Automata and Formal Systems in 3.5 hours. If I get half that, I’m lucky 😉

Amit Shah just sent me a “happy birthday” email (thanks, Amit!) with this great quotation:

Why do you want to read your code? The machine will. — Sunil Beta

Indeed!

This is the first in a series of snippets that present code that I personally consider an affront to humanity. All code must be from real, live projects. If the code is proprietary in origin, or otherwise confidential, symbol names might be changed to protect the guilty, but it’s ALL REAL. YMMV.

Today’s crime against humanity:

Returning from a within a macro

Witness this innocent chunk of code, from fs/intermezzo/journal.c in a kernel tree near you:

 
#define BUFF_ALLOC(newbuf, oldbuf)              \
        PRESTO_ALLOC(newbuf, PAGE_SIZE);        \
        if ( !newbuf ) {                        \
                if (oldbuf)                     \
                        BUFF_FREE(oldbuf);      \
                return -ENOMEM;                 \
        }

Do I really need to explain why returning from a macro is a bad, bad, bad, god awful idea? consider:

void foo(void)
{
	void* buf1, buf2, buf3; 

	BUFF_ALLOC(buf1, NULL); 
	BUFF_ALLOC(buf2, buf1); 

	BUFF_ALLOC(buf3, buf2); <----- BOOOM. Bye bye buf1 memory if
	                                      allocation fails. 
}

Resource allocation and deallocation should always be handled with care. Sequence points where resource book keeping is required must be explicit.