Older blog entries for joey (starting at number 518)

the #newinwheezy game: STM

Debian wheezy includes a bunch of excellent new Haskell libraries. I'm going to highlight one that should be interesting to non-Haskell developers, who may have struggled with writing non-buggy threaded programs in other languages: libghc-stm-dev

I had given up on most threaded programs before learning about Software Transactional Memory. Writing a correct threaded program, when multiple threads needed to modify the same state, needed careful uses of locking. In my experience, locking is almost never gotten right the first time.

A real life example I encountered is an app that displays a queue of files to be downloaded, and a list of files currently downloading. Starting a new download would go something like this:

startDownload = do
    file <- getQueuedFile
    push file currentDownLoads
    startDownloadThread file

But there's a point in time in which another thread, that refreshes the display, could then see an inconsistent state, where the file is in neither place. To fix this, you'd need to add lock checking around all accesses to the download queue and current downloads list, and lock them both here. (And be sure to always take the locks in the same order!)

But, it's worse than that, because how is getQueuedFile implemented? If the queue is empty, it needs to wait on a file being added. But how can a file be added the queue if we've locked it in order to perform this larger startDownload operation? What should be really simple code has become really complex juggling of locks.

STM deals with this in a much nicer way:

startDownload = atomically $ do
    file <- getQueuedFile
    push file currentDownLoads
    startDownloadThread file

Now the two operations are performed as one atomic transaction. It's not possible for any other thread to see an inconsistent state. No explicit locking is needed.

And, getQueuedFile can do whatever waiting it needs to, also using STM. This becomes part of the same larger transaction, in a way that cannot deadlock. It might be implemented like this:

getQueuedFile = atomically $
    if empty downloadQueue
        then retry
        else pop downloadQueue

When the queue is empty and this calls "retry", STM automatically waits for the queue to change before restarting the transaction. So this blocks until a file becomes available. It does it without any locking, and without you needing to tell explicitly tell STM what you're waiting on.

I find this beautiful, and am happier with it the more I use it in my code. Functions like getQueuedFile that run entirely in STM are building blocks that can be snapped together without worries to build more and more complex things.

For non-Haskell developers, STM is also available in Clojure, and work is underway to add it to gcc. There is also Hardware Transactional Memory coming, to speed it up. Although in my experience it's quite acceptably fast already.

However, as far as I know, all these other implementations of STM leave developers with a problem nearly as thorny as the original problem with locking. STM inherently works by detecting when a change is made that conflicts with another transaction, throwing away the change, and retrying. This means that code inside a STM transaction may run more than once.

Wait a second.. Doesn't that mean this code has a problem?

startDownload = atomically $ do
    file <- getQueuedFile
    push file currentDownLoads
    startDownloadThread file

Yes, this code is buggy! If the download thread is started, but then STM restarts the transaction, the same file will be downloaded repeatedly.

The C, Clojure, etc, STM implementations all let you write this buggy code.

Haskell, however, does not. The buggy code I showed won't even compile. The way it prevents this involves, well, monads. But essentially, it is able to use type checking to automatically determine that startDownloadThread is not safe to put in the middle of a STM transaction. You're left with no choice but to change things so the thread is only spawned once the transaction succeeds:

startDownload = do
    file <- atomically $ do
        f <- getQueuedFile
        push file currentDownLoads
        return f
    startDownloadThread file

If you appreciate that, you may want to check out some other #newinwheezy stuff like libghc-yesod-dev, a web framework that uses type checking to avoid broken urls, and also makes heavy use of threading, so is a great fit for using with STM. And libghc-quickcheck2-dev, which leverages the type system to automatically test properties about your program.

Syndicated 2013-05-02 16:54:04 from see shy jo

Template Haskell on impossible architectures

Imagine you had an excellent successful Kickstarter campaign, and during it a lot of people asked for an Android port to be made of the software. Which is written in Haskell. No problem, you'd think -- the user interface can be written as a local webapp, which will be nicely platform agnostic and so make it easy to port. Also, it's easy to promise a lot of stuff during a Kickstarter campaign. Keeps the graph going up. What could go wrong?

So, rather later you realize there is no Haskell compiler for Android. At all. But surely there will be eventually. And so you go off and build the webapp. Since Yesod seems to be the pinnacle of type-safe Haskell web frameworks, you use it. Hmm, there's this Template Haskell stuff that it uses a lot, but it only makes compiles a little slow, and the result is cool, so why not.

Then, about half-way through the project, it seems time to get around to this Android port. And, amazingly, a Haskell compiler for Android has appeared in the meantime. Like the Haskell community has your back. (Which they generally seem to.) It's early days and rough, lots of libraries need to be hacked to work, but it only takes around 2 weeks to get a port of your program that basically works.

But, no webapp. Cause nobody seems to know how to make a cross-compiling Haskell compiler do Template Haskell. (Even building a fully native compiler on Android doesn't do the trick. Perhaps you missed something though.)

At this point you can give up and write a separate Android UI (perhaps using these new Android JNI bindings for Haskell that have also appeared in the meantime). Or you can procrastinate for a while, and mull it over; consider rewriting the webapp to not use Yesod but some other framework that doesn't need Template Haskell.

Eventually you might think this: If I run ghc -ddump-splices when I'm building my Yesod code, I can see all the thousands of lines of delicious machine generated Haskell code. I just have to paste that in, in place of the Template Haskell that generated it, and I'll get a program I can build on Android! What could go wrong?

And you even try it, and yeah, it seems to work. For small amounts of code that you paste in and carefully modify and get working. Not a whole big, constantly improving webapp where every single line of html gets converted to types and lambdas that are somehow screamingly fast.

So then, let's automate this pasting. And so the EvilSplicer is born!

That's a fairly general-purpose Template Haskell splicer. First do a native build with -ddump-splices output redirected to a log file. Run the EvilSplicer to fix up the code. Then run an Android cross-compile.

But oh, the caveats. There are so many ways this can go wrong..

  • The first and most annoying problem you'll encounter is that often Template Haskell splices refer to hidden symbols that are not exported from the modules that define the splices. This lets the splices use those symbols, but prevents them being used in your code.

    This does not seem like a good part of the Template Haskell design, to be honest. It would be better if it required all symbols used in splices to be exported.

    But it can be worked around. Just use trial and error to find every Haskell library that does this, and then modify them to export all the symbols they use. And after each one, rebuild all libraries that depend on it.

    You're very unlikely to end up with more than 9 thousand lines of patches. Because that's all it took me..

  • The next problem (and the next one, and the next ...) is that while GHC's code output by -dump-splices (and indeed, by GHC error messages, etc) looks like valid Haskell code to the casual viewer, it's often not.

    To start with, it often has symbols qualified with the package and module name. ghc-prim:GHC.Types.: does not work well where code originally contained :.

    And then there's fun with multi-line strings, which sometimes cannot be parsed back in by GHC in the form it outputs them.

    And then there's the strange way GHC outputs case expressions, which is not valid Haskell at all. (It's missing some semicolons.)

    Oh, and there's the lambda expressions that GHC outputs with insufficient parentheses, leading to type errors at compile time.

    And so much more fun. Enough fun to give one the idea that this GHC output has never really been treated as code that could be run again. Because that would be a dumb thing to need to do.

  • Just to keep things interesting, the Haskell libraries used by your native GHC and your Android GHC need to be pretty much identical versions. Maybe a little wiggle room, but any version skew could cause unwanted results. Probably, most of the time, unwanted results in the form of a 3 screen long type error message.

    (My longest GHC error message seen on this odyessy was actually a full 500+ kilobytes in size. It included the complete text of Jquery and Bootstrap. At times like these you notice that GHC outputs its error messages o.n.e . c.h.a.r.a.c.t.e.r . a.t . a . t.i.m.e.)

Anyway, if you struggle with it, or pay me vast quantities of money, your program will, eventually, link. And that's all I can promise for now.


PS, I hope nobody will ever find this blog post useful in their work.

PPS, Also, if you let this put you off Haskell in any way .. well, don't. You just might want to wait a year or so before doing Haskell on Android.

Syndicated 2013-04-17 06:41:33 from see shy jo

upstream git repositories

Daniel Pocock posted The multiple repository conundrum in Linux packaging. While a generally good and useful post, which upstream developers will find helpful to understand how Debian packages their software, it contains this statement:

If it is the first download, the maintainer creates a new git repository. If it has been packaged before, he clones the repository. The important point here is that this is not the upstream repository, it is an independent repository for Debian packaging.

The only thing important about that point is that it highlights an unnecessary disconnect between the Debian developer and upstream development. One which upstream will surely find annoying and should certainly not be bothered with.

There is absolutely no technical reason to not use the upstream git repository as the basis for the git repository used in Debian packaging. I would never package software maintained in a git repository upstream and not do so.

The details are as follows:

  • For historical reasons that are continuingly vanishing in importance, Debian fetishises the tarballs produced by upstream. While upstreams increasingly consider them an unimportant distraction, Debian insists in hoarding and rolling around in on its nest of gleaming pristine tarballs.

    I wrote pristine-tar to facilitate this behavior, while also pointing fun at it, and perhaps introducing a weak spot with which to eventually slay this particular dragon. It is widely used within Debian.

    .. Anyway, the point is that it's no problem to import upstream's tarball into a clone if their git repository. It's fine if that tarball includes files not present in their git repository. Indeed, upstream can do this at release time if they like. Or Debian developers can do it and push a small quantity of data back to upstream in a branch.

  • Sometimes tagged releases in upstream git repositories differ from the files in their released tarballs. This is actually, in my experience, less due to autotools generated files, and more due to manual and imperfect release processes, human error, etc. (Arguably, autotools are a form of human error.)

    When this happens, and the Debian developer is tracking upstream git, they can quite easily modify their branch to reflect the contents of the tarball as closely as they desire. Or modify the source package uploaded to Debian to include anything left out of the tarball.

    My favorite example of this is an upstream who forgot to include their README in their released tarball. Not a made up example; as mentioned tarballs are increasingly an irrelevant side-show to upstreams. If I had been treating the tarball as canonical I would have released a package with no documentation.

  • Whenever Debian developers interact with upstream, whether it's by filing bug reports or sending patches, they're going to be referring to refs in the upstream git repository. They need to have that repository available. The closer and better the relationship with upstream, the more the DD will use that repository. Anything that pulls them away from using that repository is going to add friction to dealing with upstream.

    There have, historically, been quite a lot of sources of friction. From upstreams who choose one VCS while the DD preferred using another, to DDs low on disk space who decided to only version control the debian directory, and not the upstream source code. With disk space increasingly absurdly cheap, and the preponderance of development converging on git, there's no reason for this friction to be allowed to continue.

So using the upstream git repository is valuable. And there is absolutely no technical value, and plenty of potential friction in maintaining a history-disconnected git repository for Debian packaging.

Syndicated 2013-04-03 16:53:20 from see shy jo

Goodreads vs LibraryThing vs Free software

Four years ago I started using Goodreads to maintain the list of books I've read (which had lived in a flat text file for a decade+ before that).

Now it's been aquired by Amazon. I doubt it will survive in its current form for more than 2 years. Anyway, while Goodreads has been a quite good way to find what my friends are reading, I've been increasingly annoyed by the quality of its recommendations, and its paucity of other features I need. It really doesn't seem to help me keep up with new and interesting fiction at all, unless my friends happen to read it.

So I looked at LibraryThing. Actually, I seem to have looked at it several times before, since it had accounts named "joey", "joeyh", and "joeyhess" that were all mine. Which is what happens to me on sites that lack Openid or Browserid.

Digging a little deeper this time, I am finding its recommendations much better than Goodreads' -- although it seems to sometimes recommend books I've already read. And it has some nice features like tracking series, so you can easily tell when you've read all the books in a series or not. The analytics overall seem quite impressive. The UI is cluttered and it seems to take 5 clicks to add and rate a single book. It supports half stars.

Overall I get the feeling this was designed for a set of needs that doesn't quite match mine. For example, it seems it doesn't have a single database entry per book; instead each time I add a book, it seems to pull in data from primary sources (library of congress, Amazon cough) and treat this as a separate (but related) entry somehow. Weird. Perhaps this makes sense to say, librarians. I'm willing to adjust how I think about things if there's an underlying reason that can be grasped.

There's a quite interesting thread on LibraryThing where the founder says:

Don't say we should open-source the code. That would be a nightmare! And I have limited confidence in APIs. LibraryThing has the book geeks, but not so much the computers geeks.

I assume that the nightmare is that there would be dozens of clones of the site, all balkanized, with no data transfer, no federation between them.

Except, that's the current situation, as every Goodreads user who is now trying to use LibraryThing is discovering.

Before I ever started using Goodreads, I made sure it met my minimum criteria for putting my data into a proprietary silo: That I could get the data back out. I can, and have. LibraryThing can import it. But the import process loses data! And it's majorly clunky. If I want to continue using Goodreads due to its better UI, and get the data into LibraryThing, for its better analytics, I have to do periodic dumps and loads of CSV files with manual fixups.

This is why we have standards. This is why we're building federated social networks like status.net and the upcoming pump.io that can pass structured data between nodes transparently. It doesn't have to be a nightmare. It doesn't have to rely on proprietary APIs. We have the computer geeks.

Thing is, sites like GoodReads and LibraryThing need domain-specific knowledge, and communities to curate data, and stuff like that. Things that work well in a smallish company. (LibraryThing even has a business model that makes sense, yearly payments to store more books in it.)

With free software, it's much more appealing to sink the time we have into the most general-purpose solution we can. Why build a LibraryThing when we could build something that tracks not only books but movies and music? Why build that when we could build a generic federated network for structured social data? And that's great, as infrastructure, but if that infrastructure is only used to build a succession of proprietary data silos, what was the point?

So, could some computer & book geeks please build a free software alternative to these things, focused on books, that federates using any of the fine APIs we have available? Bear in mind that there is already a nice start at a comprehensive collection of book data in the Open Library. I'd happily contribute to a crowd funded project doing this.

Syndicated 2013-03-30 16:20:18 from see shy jo

difficulties in backing up live git repositories

But you can’t just tar.gz up the bare repositories on the server and hope for the best. Maybe a given repository will be in a valid state; maybe it won’t.

-- Jeff Mitchell in a followup to the recent KDE near git disaster

This was a surprising statement to me. I seem to remember that one of (many) selling points for git talked about back in the day was that it avoided the problem that making a simple cp (or backup) of a repository could lead to an inconsistent result. A problem that subversion repositories had, and required annoying commands to work around. (svnadmin $something -- iirc the backend FSFS fixed or avoided most of this issue.)

This prompted me to check how I handle it in ikiwiki-hosting. I must have anticipated a problem at some point, since ikisite backup takes care to lock the git repository in a way that prevents eg, incoming pushes while a backup is running. Probably, like the KDE developers, I was simply exercising reasonable caution.

The following analysis has probably been written up before (train; limited network availability; can't check), but here are some scenarios to consider:

  • A non-bare repository has two parts that can clearly get out of sync during a backup: The work tree and the .git directory.

    • The .git directory will likely be backed up first, since getdirent will typically return it first, since it gets created first . If a change is made to the work tree during that backup, and committed while the work tree is being backed up, the backup won't include that commit -- which is no particular problem and would not be surprising upon restore. Make commit again and get on with life.

    • However, if (part of) the work tree is backed up before .git, then any changes that are committed to git during the backup would not be reflected in the restored work tree, and git diff would show a reversion of those changes. After restore, care would need to be taken to reset the work tree (without losing any legitimate uncommitted changes).

  • A non-bare repository can also become broken in other ways if just the wrong state is snapshotted. For example, if a commit is in progress during a backup, .git/index.lock may exist, and prevent future commits from happening, until it's deleted. These problems can also occur if the machine dies at just the right time during a commit. Git tells you how to recover. (git could go further to avoid these problems than it does; for example it could check if .git/index.lock is actually locked using fcntl. Something I do in git-annex to make the .git/annex/index.lock file crash safe.)

  • A bare repository could be receiving a push (or a non-bare repository a pull) while the backup occurs. These are fairly similar cases, with the main difference being that a non-bare repository has the reflog, which can be used to recover from some inconsist states that could be backed up. Let's concentrate on pushes to bare repositories.

    • A pack could be in the process of being uploaded during a backup. The KDE developers apparently worried that this could result in a corrupt or inconsistent repository, but TTBOMK it cannot; git transfers the pack to a temp file and atomically renames it into place once the transfer is complete. A backup may include an excess temp file, but this can also happen if the system goes down while a push is in progress. Git cleans these things up.

    • A push first transfers the .git/objects, and then updates .git/refs. A backup might first back up the refs, and then the objects. In this case, it would lose the record that refs were pushed. After being restored, any push from another repository would update the refs, even using the objects that did get backed up. So git recovers from this, and it's not really a concern.

    • Perhaps a backup chooses to first back up the objects, and then the refs. In this case, it could back up a newly changed ref, without having backed up the referenced objects (because they arrived after the backup had finished with the objects). When this happens, your bare repository is inconsistent; you have to somehow hunt down the correct ref for the objects you do have.

      This is a bad failure mode. git could improve this, perhaps, by maintaining a reflog for bare repositories, which, in my limited testing, it does not do.

  • A "backup" of a git repository can consist of other clones of it. Which do not include .git/hooks/ scripts, .git/config settings, and potentially other valuable information, that strangely, we do not check into revision control despite having this nice revision control system available. This is the most likely failure mode with "git backups". :P

I think that it's important git support naive backups of git repositories as well as possible, because that's probably how most backups of git repositories are made. We don't all have time to carefully tune our backup systems to do something special around our git repositories to ensure we get them in a consistent state like the KDE project did, and as their experience shows, even if we do it, we can easily introduce other, unanticipated problems.

Can anyone else think of any other failure modes like these, or find holes in my slightly rushed analysis?


PS: git-annex is itself entirely crash-safe, to the best of my abilities, and also safe for naive backups. But inherits any problems with naive backups of git repositories.

Syndicated 2013-03-25 01:39:49 from see shy jo

Kickstarter rewards wrap-up

I finished delivering all my Kickstarter rewards at the end of the year. This is an overview of how that went, both financially and in general.

my Kickstarter pie (not including taxes)

While the Kickstarter was under way, several friends warned me that I might end up spending a lot of the money for rewards, or even shipping, and come out a loser. It's happened to some people, but I avoided it. Most of the pie went to its intended purpose.

USB key arrives in Amsterdam

I kept shipping cost low by shipping everything by US postal service, including Air Mail for international shipping. This was particularly important for the stickers (which cost $1.05 to ship internationally). But I also shipped USB keys in regular mail envelopes, protected by bubble wrap, which worked very well and avoided the bother of shipping packages. The USPS will be annoyed at you for a rigid letter and add a non-machinable surcharge, but it's still a nice savings.

expenses

I spent more on rewards than on transaction fees, but the fees are still pretty large. Being dinged a second time by Amazon is the worst part. I have not been able to work out exactly what formula Kickstarter uses to determine its fee per pledge. It does not seem to be a simple percentage of the pledge. For example, they seem to have charged $0.25 per $10 pledge, but $25 for a $500 pledge. I wanted to solve this, but I'd have to match up all the pledges and fees manually to do it.

gross income by reward type

This chart is slightly innacurrate, because it puts any money pledged, beyond the amount needed to get a reward, into the "intangibles" category, despite the reward being probably responsible for that money being pledged.

(The intangibles also includes people who did not ask for a reward, and several categories of rewards not involving shipping matter around.)

But, the surprise for me is how large a peice the T-shirts are responsible for. It was my least favorite reward, and a low volume one, but I made out pretty well on it. However, I'd still try to avoid putting T-shirts on Kickstarter again. It's hard to do a good design (I didn't, really); they're expensive, and were by far the most annoying thing to ship. Also, I was not happy with the countries Cafe Press sourced their shirts from; I've been to Honduras and talked with people who have relatives in las machinas.

gross and net income by reward type (excluding shipping)

In contrast, the stickers had an amazing margin; they're so inexpensive to print that I printed up two kinds and included multiple with every other reward I mailed. I still have hundreds left over, too.. All the online print shops I tried have very annoying interfaces to upload artwork though. I had to do quite a bit of math to render TIFF files with appropriate DPI and margins.

The USB keys were my favorite reward. I got them from USB Memory Direct, who gave me quite a nice deal. I was very happy that I was able to send them a SVG file of my artwork, so I didn't need to worry about lacking resolution for the laser engraving. And it came out looking great.

The best part was when their sales guy Mike actually did a minor alteration of the artwork, to better fit on the key, when I, being overloaded with Kickstarter stuff asked him too. A bit above and beyond.

There was an issue with their Chinese manufacturer's quality control of the 16 gb drives, but they were willing to send me replacement for all the ones I found problems with.


All told I spent probably 3 full days stuffing and shipping envelopes, and probably spent a week working on Kickstarter reward fullfillment. As work-related overhead goes, that's not bad. Maybe someone considering a Kickstarter will find this information useful somehow. Oh well, back to work. :)

Syndicated 2013-02-21 01:00:30 from see shy jo

Sydney nostalgia

Sydney opera house viewed from a ferry

Last Saturday, when the bus from Canberra pulled into Sydney's central station, I found myself feeling curiously nostalgic for this city, and particularly this bustling and somewhat seedy[1] neighborhood of Haymarket and Redfern.

glowing angels in Kimber lane

I only spent 5 days in Sydney, but living in a shared house there, walking up to Central every day, and returning to the outskirts of the Haymarket every evening to slurp noodles or other asian food, I got into a routine. And got a sense of the place that goes perhaps a bit beyond the tourist sights.

Manly beach panorama

Perhaps if I'd had more time I would have found a decent coffee shop that had both free wifi and abundant seating. They seem scarce in Sydney. I instead often got on the ferry to Manly when I wanted some sit down and code time.

Cliffside Protect Our Water Dragons sign
One time when I was exploring the headlands above Manly beach, I noticed this sign.
Then I ran into this guy. Click him for an amusing video.
lizard

Anyway, Sydney is on my very short list of cities I'd actually enjoy spending some more time in some day, along with San Francisco, Vancouver, Oslo, and London.


[1] Depending on what's inside all the "VIP lounges" and "Thai massage parlours" on every corner that I did not explore, perhaps thoroughly seedy?

Syndicated 2013-02-07 16:35:49 from see shy jo

LCA2013 wrapup

After 27 hours of travel, I'm finally back from my first Linux.conf.au.

This was a great conference! Some of my favorite highlights:

  • Out for dinner the first night, my whole table started spontaneously talking about Haskell, including details of IO management frameworks like conduit and pipes, and a new one that's waiting in the wings. That just doesn't happen in the real world. A lot of us continued to do Haskell stuff in the hallway track, although for some reason there were no Haskell talks on the official schedule. Maybe it's time for a Haskell miniconf at LCA?
  • Meeting Josh, Jamie, Sarah, Brendan, Craig, and others I've worked with online but never encountered IRL. Also reconnecting with old friends (some I'd not seen in 13 years) and finding new ones.
  • The speaker's dinner in a revolving restaurant overlooking Canberra. Leave it to a restaurant full of geeks to invent an asychronous communications medium in such a setting. (Notes attached to windows to be read and answered by tables as they rotated by.)
  • Meeting quite a lot of git-annex users, Kickstarter backers, and people interested in using git-annex. Thanks to everyone who came up to me for a chat.
  • The evening pickup board game sessions. Especially my wiping out three other Tsuro players at once by forcing them all to end on the same square. ;) These were where I felt the most at home in Australia.
  • Robert Llewellyn dropping in and mingling with fans of Red Dwarf and Scrapheap Challenge. One of the very few actors I could possibly fanboy on, and LCA not only somehow got him, but constructed an atmosphere that allowed for this photo of us.


My git-annex talk went ok, despite technical problems with the video output, which the video team did a great job of working around. The first demo went well, and the Q&A was excellent.

The demo of the git-annex assistant webapp was marred by, apparently, a bad build of the webapp -- which I ironically used rather than my usual development build because I assumed it'd be less likely to fail. At least I may have a way to reproduce that hang somewhat reliably now, so I can get on with debugging it. I will be redoing a demo of the webapp as a screencast.


Here are some of the best talks I attended. (I have quite a lot more queued up to watch still, and had to cut several due to space.) Click titles for videos, or browse all the videos.

  • Git for Ages 4 and Up
    Schwern has found a new, excellent way to explain git. I felt rather bad for using up a seat, especially once people were kicked out when the room was filled over capacity. But I enjoyed every minute of it. (Also has the best speaker intro ever. "Schwern once typed git pull --hard and pulled GitHub's sever room across the street.")

    BTW, I must confess: I left the red apple on teacher's desk.
  • Radia Perlman's keynote
    Network protocol design and poetry from one of the quiet heros of our field. I knew Spanning Tree Protocol was used in ethernet, but it just works, so like many I never paid much attention to it. This talk felt like the best lectures, where you're learning from a master on multiple levels at once. Well done work often becomes an unremarked part of the landscape, which I sometimes find unrewarding, so it was great to have Radia give some perspective on what that's like over the course of decades.

  • Lightning Talks
    A 90 second time limit really helps. Too many conferences have 5 minute talks, which is less exciting. If you still find them boring, skip forward to 13:50, where pjf does two talks in 90 seconds! (If a 20 second talk on depression is too .. manic, there's an encore at the end.)

  • The IPocalypse 20 months later
    A reality check, with real data. Very important stuff here. We need to work to avoid this worst case scenario, and we also need to design around it.

  • REPENT!!! FOR THE END OF THE UNIX EPOCH IS NIGH!!!
    Wildest talk beginning I've seen since RMS put the hard drive halo on his head. And to an important point: Any programs that deal with dates 25 years in the future already need to be fixed today to deal with the epoch rollover. This got me digging around in Haskell date libraries, to make sure they're ok.

  • Building Persona: Federated and Privacy Sensitive Identity for the Web
    This talk and some previous conversation with Francois have convinced me that Persona (AKA Browserid) has a design that can succeed. I will be adding Persona login support to ikiwiki.

  • Beyond Alt Text: What Every Project Should Know About Accessibility
    I missed the first half due to giving my talk, but the second half was full of rather a lot of excellent information, some of which I'd only guessed at before.

  • Git: Not Just for Source Code Anymore
    Good overview of the new ways to use git. Also kept giving examples from my body of work, which is some nice ego stroking, thanks Josh. ;-)

Syndicated 2013-02-05 03:44:45 from see shy jo

in Sydney

After arriving yesterday, and doing the obligatory jetlagged wander around Circular Quay to the Opera House, I crashed for 15 hours sleep and seem reasonably well over the jetlag now. I'm staying near Central Station, which is great because it's very convenient to transport and there's lots of cheap ethnic food.

view down my street

Today I took the ferry over to Manly Beach. I had to get in some in swimming of course, although today was cloudy and only in the 80's (F). That was ok, but the really nice bit was walking over to Shelly Beach and up along the sandstone cliffs near North Head.

Highlight was finding a small gotto high on the cliff, with some beautiful sandstone filigree overhead, that seemed carved by water (but probably really by wind), and contained a shady bench overlooking the Pacific. Great place to enjoy a lunch of crusty bread and salami if you're ever in the area.

Topped off a great day with a random trip to Neutral Bay (the D&Der in me liked the name, and why not, ferries are free) and a wander through the Royal Botanic Gardens.

I'm hoping to spend either Thursday or Friday at a co-working or hackerspace in Sydney, but I don't know where yet. Any locals have ideas?

Syndicated 2013-01-23 06:56:49 from see shy jo

overcast

My least favorite forecast, and we've been having a lot of it lately. Since winter began (Dec 21st), my PV array has produced only 102 amp-hours of power. There have been only 3 days that could be considered sunny at all (even for a few hours). To put this in some perspective for you, Wolfram Alpha tells me that 102 amp-hours is half of a typical car battery capacity. So I've really had to scrimp & save. I disconnected my router to save power, and I plumbed the depths of the battery bank (further than it's really safe to go). And I was completely out of power for several days.

So, I've bought a generator. I had to order it online, because it seems every store in the entire eastern US is completly out of stock, due to hurricane Sandy. This house has a generator shed (complete with a massive old generator that doesn't work), but I put the new, small generator in the furthest outbuilding, from where it can only barely be heard in the house. Later I'll be able to run a cable from its 12v terminal to charge the battery bank (if the sun doesn't get there first); for now it only powers my laptop. Nasty noisy smelly dirty thing, it pains me to run it.

Back to the "overcast" forecast. I've heard meterologists say that one unexpected consequence of climate change seems to be that weather patterns are persisting longer, giving us this summer's weeks of neverending heat, and large, slow-moving storms. I suspect this could also explain the blankets of clouds that have been settling in for weeks at a time, on and off since mid-November. But I only have 2.5 years of not very good data. Before, I paid about as much attention to whether it was sunny as anyone else, which is to say, not really very much. Anyone know of a source of historical cloud cover data?

Syndicated 2013-01-03 17:25:08 from see shy jo

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