Older blog entries for itamar (starting at number 13)

24 Nov 2002 (updated 20 Mar 2003 at 05:15 UTC) »

This used to be a post with me complaining about Linksys and Seth Bromberger. Seems like I was wrong, and he did find the vulnerability two weeks before I did, so I aplogize to him and Linksys.

I submitted the paper glyph and I wrote for Usenix '2003, 25 minutes before the deadline. I hope they accept it.

17 Nov 2002 (updated 17 Nov 2002 at 05:36 UTC) »

I added multicast support to Twisted. Or to be more accurate, the tests for the multicast code pass - I have no idea if it works in the real world, and probably won't until we get a Real User to use the code.

Together with the rewrite of the old UDP API, we now support (in theory :) another small corner of the networking world.

Exceptions in signal handlers

I realized the issue isn't just with exceptions - it can be with any operation (e.g. log rotation on a signal might be interrupting a log write method, and who knows what happens then).

Yet another benefit of event loops is that the problem is easier to solve. Instead of raising an exception (or rotating the log or whatever), you do this by registering a method to run in the next iteration of the event loop. Because you are forced to split up your tasks into small, self-contained, short running event handlers anyway, your program by design will be much easier to structure so that this is not a problem. So, instead of rotating log on signal, you would tell event loop to run log rotation method in its next iteration.

I'm going to have to change Twisted's rotate-log-on-signal code and possibly other signal handlers so they work that way, if they don't already.

Software Methodology

My father wrote a paper on software methodologies which might be of interest to people here, especially if you're interesting in agile programming and the like.

On Saturday I was at the Lightweight Languages Workshop at MIT, and here are notes about some of the talks. There's a webcast available from the website.


First talk was Erlang, which is very interesting. It's a functional language, and designed for concurrency - you can launch tens of thousands of processes, and pass messages between them. And this is done fast - 2 microseconds to start a process. Apparently Oz shares a lot of the concepts here as well.

OS-level services in Scheme

Second talk was about the ways PLT Scheme (MzScheme?) is incorporating OS-level functionality into the language.

PLT Scheme OS-like capabilities that I found interesting:

  • killing threads cleanly
  • Indepent GUI eventspaces (e.g. independent regarding modal dialogs).
  • custodian manages resources for threads so you can easily shut it down.
  • enforce abstractions (like Java's private?) and then add hooks for bypassing it for debugging.

This is very useful for IDEs. They have example IDE that lets you run say, infinite loop in interpreter, without the GUI freezing up, and because you can kill threads you can cancel this operation. In addition, GUI you program via IDE runs in its own event loop so it doesn't interfere with IDE's event loop.

Apparently the author is spending a lot of time making the blocking OS level facilities not block, so he can do this sort of thing.

Asynchronous Exceptions in Python

The fourth talk was about raising exceptions in signal handlers in Python, and the problem this causes. Basically the issue is that in e.g. this code:

f = open("file")
    s = f.read()

the file may never be closed, since a signal might raise an exception right after file is opened but before try/finally. The obvious solution is too disable the signal around this code, but this is TOO MUCH TYPING, and you MIGHT FORGET to reenable the signal. So what was suggested? Adding new keywords! They gave following example code:

    f = open("f")
            s = f.read()

where block/unblock do that to signals. I think this is terribly wrong. First of all, their own example was wrong, it should actually have been:

    f = open("f")
            s = f.read()

This is totally ridiculous - you need to wrap each block of code this way, it blocks all signals instead of just the appropriate one, and the syntax totally violates the standard behavior of existing keyword pairs in python, since they are on different indentation levels.

I think raising exceptions from signal handlers is just a messy idiom, and they just shouldn't be doing it. And given you don't need a keyword to solve the problem, you just can use the signal module, their suggestion is just badly implemented syntactic sugar, with side effects that extend beyond the problem they want to solve.

I might write up the rest of the talks tommorow.

11 Nov 2002 (updated 11 Nov 2002 at 05:31 UTC) »

Cory Dodt suggested paying Iraqi soldiers to surrender. This actually works quite well - lets say you have 100,000 Iraqi soldiers. If we give each 1 million US$ to surrender, that comes to $100 billion - half the projected cost of the war. Quote from #twisted:

or maybe just pay his army to surrender. it would cost less than shipping 250,000 troops over there, i'll bet you. the oil companies would probably chip in too
we could get everyone involved. like sponsoring a starving child in africa. except you're sponsoring an iraqi to surrender.
i wonder if we could get them to write their sponsors letters. "thank you for not blowing me up. thanks to your generous donation of 1 million dollars, instead of being dead, i am now an oil magnate in my native country."

Tommorow I'll post my summary of Little Languages Workshop (preview - Erlang, I ask stupid questions and get put down in public, suggested Python atrocities, and more).

The International ANSWER coalition organized the Oct. 26 anti-war demonstration. There were between 100,000 and 200,000 in Washington DC, and another 20-80 thousand in San Francisco. That comes to a total of about a quarter of a million people. I was at the DC one, and did my small part to help organize it in the NY branch, and it was very impressive indeed.

VoteNoWar.org is their next effort, leading up to a Peace Congress and another, hopefully larger, demonstration, once more in DC. Please help out - sign it, donate, volunteer with your local organizations, pass it on to all your friends.

Raph Levien has kindly retrieved my password for me, so I can post once more. Thanks!

Inspired by mjcox, I wrote a python script to download Advogato diary entries and parse them into a useful form, for embedding into other pages: http://itamarst.org/downloads/

People pointed out on my article on multiplexing, reinventing the wheel tends to be a waste of team. I don't really agree (you get to learn how wheels are made), but they do have a point. The point being that you'll get ahead a lot faster if you use an existing implementation.

So I (temporarily) stopped using my multiplexing code and switched to multiple connections as in http. This let me concentrate on the imporant parts and not get stuck with bugs in the mux code, Once I'm done I'll switch back to my code or BXXP if it's ready.

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