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Back on the air

Posted by Dominic Cronin at May 25, 2008 08:25 PM |

I'm sorry. This blog and all my web sites have been off the air for about a week. I got overconfident and decided that recompiling my linux kernel would be safe enough to risk. After all - I wanted to enable some features that need to be baked in to the kernel; specifically, support for some virtualisation that would get me out of the open source equivalent of dll hell. In theory, I should have been able to build the new kernel, add it to my boot loader configuration, and reboot the machine. If anything went wrong, well I still had the old kernel, and I could reboot using that in another few minutes.

That's the theory. In practice, I ended up spending whatever-spare-time-a-father-of-three-has for the last week relearning half of what I knew about the gentoo boot process, and then learning some more, and then eventually solving it all by just blindly updating everything and hoping.

I got quite some help from people on the relevant IRC channels (#gentoo and #gentoo-chat on freenode) and in the process ended up explaining to them that I don't believe Windows, Linux, MacOs or any such thing to be superior to the others. It's mostly about what you are familiar with, and I have maybe five years on linux, compared to three or four times that on Windows as a professional. To be fair, such places aren't the sweaty hotbeds of rabid linux-advocacy that you might imagine. Most people have solid time on Windows too, but it's a really hard sell to suggest that usability is even vaguely important. If you can't take the heat, stay out of the kitchen, I suppose....

Noise is toxic to programming

Posted by Dominic Cronin at May 16, 2008 07:45 PM |

This one is going round again after Steve McConnell recently posted his regular re-issue of Software's classic mistakes, in which "noisy, crowded offices" is ranked 8th. Jurgen Appelo picks this up and riffs on it a bit in Tear down your cubicle walls, and makes a few nice points. In general, he's on the side of the angels but I disagree with him on a few things.

Firstly, he argues against the claim in Peopleware that open offices are bad for productivity. He's following the fairly standard agilist line about war-rooms; people working on the same project should all sit together. I've had some recent experience of a project war-room proving to be a success, and I've openly advocated this approach, but let us not forget that this is second best. Best - by a long way, is private or double rooms combined with suitable team spaces to allow for collaboration. That's how it's done at the most successful software company on the planet, and they ain't hippies; Microsoft's approach is based on solid psychological analysis of people's work requirements, and computer programmers are classified as "concentrators".  Having said that, their Workplace Advantage programme does seem to include moving non-concentrators out of private offices.

The other point I'd like to pick up on is his "rules" which apparently are intended to make open-plan working bearable:

"No yelling. No running. No meetings (except for 15-minute stand-ups). And no disturbing of people when they're wearing headphones. (Many of us like listening to their favorite music while working.)"

You see this so often. People are forced into working in open-plan offices, and they compensate by wearing headphones and listening to music. It doesn't solve the problem  - it only masks it, and it only works for the people who can put up with the stupidity of it for long enough. Listening to music while working actually steals thinking cycles. You aren't as smart listening to music as you are in silence. Having said that, you are probably smarter listening to music than listening to the hubbub of your colleagues.

In the past, I've tried using white-noise in place of music, but that also has a pretty high vacuum rating.

Bottom line. Rooms are more expensive than open space. Highly valued employees tend to be given rooms. The rest have to suffer the rhetoric of rationalisation.

From the horse's mouth... a hot content portering tip (and a bit of a rant)

Posted by Dominic Cronin at Mar 23, 2008 09:25 AM |
Filed under: ,

I have to admit, I nearly choked when I saw this. Bear with me a moment, and I'll tell you all about it.

Not so very long back, I was trying to set up the SDL Tridion Content Porter to work as part of an automated "build" system. One of the requirements was that I'd be able to save content and then re-import it into various different publications. After all, you need a go-to-production option as well as being able to support development and test work. After beating my brains out trying to figure out the publication mapping features in Content Porter, I asked around a bit, and found that lots of people have trouble with this, and one well-favoured option is just to go round the problem and run regexes against the entire intermediate file set to swap publication names. Oh-kaay - so a couple of hours later I'd hacked out some javascript that would do this, and solving the mapping problem the official way promptly went on the back burner, perhaps for ever (or at least until the pan boils dry). Moral of the story: doing it the official way is just too stupidly hard.

So on with the tale: This morning I was installing SDL Tridion Webforms on my research image. This was the first time I've installed WebForms, so I was stepping gently through the documentation when I realised that the WebForms installation relies on Content Porter. OK then - a quick excursion to install Content Porter, configure the Business Connector etc., and back to the main plot. That's when I nearly choked. The documentation for the WebForms installation contains this little gem:

When you perform this import, Content Porter creates a Publication called WebForms. Once created, this Publication contains the items that you need in order to use WebForms Designer and WebForms Field Type Editor. Alternatively, you can also import WebForms items into an existing Publication. Note To import WebForms into an existing Publication, rename the Publication to which you want to import the items to WebForms before you run Content Porter. Then, after you have used Content Porter, rename the Publication back to its original name.

So there you have it: according to Tridion, the correct way to solve this problem is to rename the publication, and then rename it back again afterwards. Let's hope that's an OK thing to do in your environment.

To tell the truth, I quite like this as a "hack". It's robust and solid, and very definitely gets the job done. In fact, it's about as nice a job of working around Content Porter's limitations as you'll find. I wish I'd thought of it myself. In fact, part of the reason for this post is as a public service announcement for anyone who doesn't happen to spend their Sunday mornings reading the WebForms installation manual.

But please, Tridion. Isn't this a wake-up call? When your own product installation guides have to give out workarounds like this. I know there's a new version of Content Porter on the roadmap, and I very sincerely hope that it's going to come with batteries included. While I'm on the subject - this is what the WebForms installation guide says a couple of lines further down:

Due to dependencies between items that you are importing, you will have to run the Content Porter twice in order to import all items used by SDL Tridion WebForms Designer. The first time that you run the Content Porter, you will receive error messages during the import process. These messages are not critical. You can click "Skip All" to continue.

The Content Porter should manage this. If the import of an item fails because its dependencies aren't there yet, and the dependencies are there in the package, then just wait until the end and redo it. Automatically! Rinse and repeat. Why inflict this misery on end users? There's a very real use case for Content Porter where you want to produce a package to give to someone else to import, and you don't want them worried by this kind of nonsense.  If there's any reason for the existence of Content Porter, it's the managing of depencies between the items being imported.

End-user misery aside - I should be able to use the Content Porter as part of an automated solution, and that just won't fly while I have to know in advance that a particular package requires two or more attempts to succeed.



Why is Tridion's configuration library called the TDSXGit?

Posted by Dominic Cronin at Mar 09, 2008 07:05 PM |
Filed under: ,

Those of you who read my previous post will remember that I accessed Tridion's configuration by instantiating a TDSXGit.Configuration object. People who've worked with Tridion for a while may remember that it used to be quite common to edit the configuration in a file called cm_cnfg_git.xml. This file is still there, but without the xml extension, and these days it's encrypted so it doesn't make much sense to try to edit it directly.

To an Englishman like myself, this name TDSXGit is vaguely funny, because "git" in British English is a mild term of abuse. It's not uncommon for me to come out with phrases like: "Which stupid git broke the build"? It's definitely abuse, but fairly mild; you can say it to someone that you like. 

But to the point: Back in the R4 days, Tridion's configuration data was kept in the registry, which was all well and good, but had it's own problems. When R5 was designed, there was so much XML around the place that it seemed much more sensible to keep the configuration in an XML file. The problem with this was that all that disk IO would have been a total performance killer. We needed a memory cache. Good idea, you might think, but in a COM-based web application, how do you do that? The design we ended up with makes use of a couple of fairly obscure features of COM. (By the way - I'm not claiming any credit for this, just describing what was designed by other members of the team.)

The idea is to get an object to remain in memory, and to provide a mechanism whereby any code within the application can grab a reference to the object. In COM, a reference to an object is always a pointer to an interface. Memory access in COM is controlled by "apartments" - objects running in one apartment can't directly access objects running in another apartment.  In particular, if you have an interface pointer for an object in one apartment, you can't just use that pointer from a different apartment. The interface pointer needs to be "marshalled" across the apartment boundary; in other words, if you should be talking to a proxy that's local to your apartment, you'll get a pointer to that instead.  The mechanism for doing this is called the global interface table, hence the acronym GIT.

The GIT is visible from anywhere in the process, and if you register an interface with the GIT, that immediately takes place of the first problem, that of keeping the object in memory. In COM, memory management is done by reference counting. An object keeps track of how many other objects currently have a reference to it, and if that number drops to zero, the object will self-destruct, thereby freeing any memory it was using. As soon as you register an object with the GIT, well the GIT has a reference to it, and therefore it isn't going to self destruct, so you have your memory cache.

When you register an object with the GIT, the API hands you back a "cookie". A cookie in this context is just a number. If you know this number, you can ask the GIT for an interface pointer that references the object. You can keep doing this as many times as you like, unless there's been an explicit call to release the object from the GIT. The interface pointer you get back will work in the apartment you are in.

There's one more thing that you need to make this all work, and that's a way of making sure the cookie is always available when you need to get hold of your memory cache. For this, you can use another obscure COM feature: the shared properties manager (SPM). This just allows you to save a value by name and retrieve it. (The SPM also takes care of a couple of other things, like grouping the properties to prevent name collisions, and locking to control access contentions.)

So when a Tridion process first accesses the configuration, the configuration file will be decrypted and loaded into a DOM object, and the DOM will be registered with the GIT. The cookie is then stored in the SPM. Any subsequent accesses for the life of the process will be simply a matter of grabbing the cookie from the SPM and using it to get the interface pointer from the GIT.

There are other techniques that could be used, but this has the advantage not only of eliminating disk IO, but also repeated parsing of the XML to create the DOM.

This should explain why when you update some configuration value, you have to shut down each of the processes that make use of the configuration. The GIT and SPM are each specific to a process. It is technically possible to get TDSXGit.Configuration to release the DOM from the GIT, but none of Tridion's application code actually does this. That's a reasonable design for a server application that isn't re-configured very often.

In theory (at least according to the theory I just described), it should only be necessary to restart a process if it is affected by the configuration value that just changed, but my own experience flies in the face of this, and I always restart all the processes. It's a bit of a cargo cult thing I suppose, but I'll keep doing it. Actually, I'd love someone to point out where my reasoning is flawed. I hate that cargo cult thing.

"Which stupid git forgot to restart the processes after that configuration change?"

Am I an engineer?

Posted by Dominic Cronin at Jan 27, 2008 10:25 PM |
Filed under:

I've been following the recent discussion between Raganwald and Ravi Mohan (among others). It's the classic debate about how you define an engineer. Does the term "engineer" denote a "profession", and who is qualified to be in it? Well first of all, let me be open about my own affiliations. I'm an associate member of the Institution of Mechanical Engineers. The "associate" part, means that I'm not a corporate member, and therefore not a full member of the profession. I stopped doing mechanical engineering, in order to switch to writing software, at just about the point that if I'd have stayed, I'd have registered for full membership. (I had my degree, and a couple of years of professional experience under my belt). To achieve chartered engineer status these days, the obvious route would be to join the British Computer Society, who fulfill the same role as the IMechE but for software engineers.

So let's start there. I am an engineer. I have a good degree in mechanical engineering from a good college. I spent significant parts of my life creating engineering designs on a good-old-fashioned drawing-board, and those designs were implemented and proved in practice. I can do mathematics, both continuous and discrete. (Mechanical engineering tends to use continuous techniques like the differential and integral calculi, while computer science leans towards discrete mathmatics like set theory and so forth.) These days, I implement working computer systems in the best way I know how.

Still - I don't often use the word "engineer" to describe what I do. These days, I write software, and to do so I spend significant amounts of time studying best practices, and honing my art, but most of the time I use the word "technician" to describe my role. Let's be clear. I don't for a moment doubt my right to use the term "engineer" to describe myself. The reason I don't do so is mostly because I wonder whether other people would understand the sense in which I use the term (or perhaps I fear that I'd have to explain at great length).

Let's go back to the beginning of the great professional bodies of the engineering world. My own institution, the IMechE, was an offshoot of the Institition of Civil Engineers, back when the railway guys were carving out new territory, and the existing profession wouldn't recognise them (mostly because of their affiliations with vested interests in the world of canals.  But in those days, what made an engineer, and what made an engineering profession? The answer might upset some people's precious sensibilities, but it's simple. Engineers were people who could build working systems, and the early meetings of the profession were probably more akin to a geek dinner than anything else. George Stephenson didn't have a degree, but he could build railway engines.

Following Ravi's link to a job description which illustrates his view of what constitutes an engineer, we find the following quote:

"You have a good sense for distributed systems practice: you can reason about churn and locality in DHTs. You intuitively know when to apply ordered communication and when to use transactions. You can reason about data consistency in a system where hundreds of nodes are geographically distributed. You know why for example autonomy and symmetry are important properties for distributed systems design. You like the elegance of systems based on epidemic techniques."

The only thing of note that I can see in there is the repeated phrase "You can reason about...". (OK - I also like 'you have a good sense for...' and 'you like the elegance of...', but they aren't crucial).

An engineer can reason about his subject. He ensures that he has sufficient raw material at hand for his reasoning, but the reasoning is the thing that counts. If you can reason about technical systems, you are an engineer. If you can't, you aren't. To reason effectively, you must know the subject well, but let's take that as a given. Mathematics is a tool - perhaps we might argue that subjects which don't require mathematics aren't engineering subjects - but it's just a tool, not the essence. I suspect George Stevenson had less mathematics at his disposal than I needed to satisfy the examiners for my degree all those years ago. Never mind that. He could have shown you a working steam engine, and told you how it worked. He managed to found an engineering institution for which I don't even have the entry qualifications.

The beginnings of the engineering profession were a bunch of people saying: "Hey guys, let's meet in a pub every so often and discuss what works and what doesn't." Implicitly, if you were interested in sharpening your tools, you were invited, and if you weren't, you weren't.

I still wonder whether I'll ever make the time to do the BCS exams and work towards recognition as a Chartered Engineer. At the current rate, it might be after I retire. Until then, I'll still keep on calling myself an engineer, and keep on reasoning and sharpening my tools.

The most significant SF and Fantasy books of the last 50 years (or thereabouts)

Posted by Dominic Cronin at Jan 20, 2008 08:55 PM |

Picking up the meme-let from Nazgul, I've taken the Science Fiction Book club's list of The Most Significant SF & Fantasy Books of the Last 50 Years, 1953-2002, and filtered out the ones I haven't read.

1. The Lord of the Rings, J.R.R. Tolkien
2. The Foundation Trilogy, Isaac Asimov
3. Dune, Frank Herbert
4. Stranger in a Strange Land, Robert A. Heinlein
5. A Wizard of Earthsea, Ursula K. Le Guin
6. Neuromancer, William Gibson
7. Childhood's End, Arthur C. Clarke
8. Do Androids Dream of Electric Sheep?, Philip K. Dick
10. Fahrenheit 451, Ray Bradbury
13. The Caves of Steel, Isaac Asimov
15. Cities in Flight, James Blish
16. The Colour of Magic, Terry Pratchett
21. Dragonflight, Anne McCaffrey
23. The First Chronicles of Thomas Covenant the Unbeliever, Stephen R. Donaldson
24. The Forever War, Joe Haldeman
26. Harry Potter and the Philosopher's Stone, J.K. Rowling
27. The Hitchhiker's Guide to the Galaxy, Douglas Adams
30. The Left Hand of Darkness, Ursula K. Le Guin
38. Rendezvous with Rama, Arthur C. Clarke
39. Ringworld, Larry Niven
42. Slaughterhouse-5, Kurt Vonnegut
46. Starship Troopers, Robert A. Heinlein
47. Stormbringer, Michael Moorcock
48. The Sword of Shannara, Terry Brooks

To tell the truth, among the remaining items are several that I might have read, but I didn't remember the book as such. That's probably because I haven't actively read science fiction for about 10 years. How you get from being a complete SF&F nut to someone that never reads fiction is another story.

Making rankings like this is always going to be controversial, but I suspect that my own approach would be to choose the authors I wanted to have represented, and then try to figure out for each which was their master work, and decide whether they need to be represented more. So Lord of the Rings represents Tolkien quite adequately, but surely the Silmarilion (which I never read) was only for the people whose appetite wasn't sated by multiple re-reads of LOTR. The Foundation trilogy is a good start, but I, Robot clearly outranks some of the rubbish that's been included. Yes - for prolific core SF authors like Asimov and Clarke you need to have more than one entry. (For Clarke, I'd add the Fountains of Paradise).

For some of the other authors, the book listed is clearly not their master work. Starship Troopers for Heinlein? Surely not. I agree with Le Guin being represented for both F and SF, although for the latter, I'd have said The Disposessed was a better choice. Whatever - Earthsea was her master work.

Why is Harry Potter in there at all? Surely you could toss in a few Harry Harrisons and a few extra Nivens to push him off the bottom of the list. I guess somebody thought "significant" had something to do with box office. In that case, let's have Star Wars.

Maybe one of these days I'll start reading again... but I wouldn't know where to start. I think mostly what stops me is the thought that I won't be able to get sufficient momentum to actually get through a book, let alone give it respect.

PWN'ed at Egmond

Posted by Dominic Cronin at Jan 19, 2008 10:15 PM |

The 36th Egmond Half Marathon took place last Sunday (13th January). Thirty Six years is an impressive score; they began long before distance running became popular. Anyway - for some bizarre reason, after finishing the Amsterdam half, I signed up for Egmond, regardless of the fact that the last time I did anything cross-country was at school. The Egmond event begins with 3-4 kilometres through the village, followed by a 7 kilometre stretch along the beach. From there, you come back along peat paths through the dunes until you eventually get onto brick paths that take you back to the village and the finish line.


My official time from the chip was 1:56:53, placing me 3339 out of 6174.

The official timing also gave me a split at the half way point (10.5 km) of 57:46.

From my own watch I took splits at 10 and 15 km, as follows:

10km: 53:29:00
15km: 1:22:47:20

so as you can see, it was slow going. I was pleased just to get round the course in one piece.

The event was sponsored by PWN, a local water company (I think). So anyway - I've been PWN'd. Pure water and Nature. To tell the truth, when you're plodding along that beach, you aren't much thinking about the beauties of nature. At one point in the dunes, I looked up and for want of something positive with which to exercise my mind, I paid particular attention to the aforementioned beauties. You've still got to keep putting one foot in front of the other....

Anyway - as it turns out, the last post to this blog was when I finished the Amsterdam half. Time I started writing some technical posts.

Amsterdam half-marathon - a new personal best

Posted by Dominic Cronin at Oct 21, 2007 04:55 PM |

The Amsterdam half-marathon is, like the marathon that's run on the same day, known for fast times - partly because of a generally flat course, and partly because being this late in the year, the chance of the weather being too hot is less. For me, especially when making a comparison with the Great North Run, the fact that it's a comparatively smaller event made a big difference too. For the last two-thirds of the race I was running in open space most of the time. I was therefore able to follow my plan of getting up to a good rate of work early on and sticking to it. Most of the time I had an eye on my heart rate monitor, and kept it in the high 160's. At the end, the average rate was 166. For me that's good steady work. I don't think I could sustain, say 170 over that distance. Something to do with  being an old git. That means that if I'm to improve on my times, I'll need to raise my general level of fitness. That sounds like lots of unpleasant speed work - if I decide to try to improve on this result.

According to the official results page my net time was 1:45:21 - they also quote a gross time (1:48:13), which is presumably the time from the starting gun to when you cross the line. In this modern world where the progress of your "chip" is monitored round the course, I'm quite happy to accept the net time: start line to finish line, as the result. Back in the 1994 Great North Run, I did 1:48, and that was the time from my own stopwatch: start line to finish. Today's time is therefore my personal best over this distance. Um - OK - it's only my third half-marathon ever, so talking about personal bests might be a bit precious, but I'm really pleased with this, as my previous PB was set 13 years ago.

The official results also include some rather bizarre split times. This comes about because the positions of the mats were relative to the start line of the marathon, which was different to the start for the half-marathon. (I don't have any timings from my own watch, as I pushed the wrong button at the 5km mark. Thank goodness for the chip.)

8,9 kilometer 43:05
13,9 kilometer 1:08:27
18,9 kilometer 1:34:28

My position was 2279 / 8439. That will do nicely. I mean you can take this all too far. The memorable image of the day was Emmanuel Mutai crossing the line after running the marathon in 2:06:27. He'd given his all, and as he rounded the track in the Olympic Stadium, approaching the finish line, you could see he was having trouble. As he crossed the line, he promptly threw up. That shows just how much these top athletes push themselves. I'll settle for less.

Great North Run completed

Posted by Dominic Cronin at Oct 01, 2007 06:55 PM |

Yesterday I took part in the Great North Run. According to the official results page, my time was 1:56:49, which I suppose I'm quite pleased with under the circumstances. It was a warm day, and starting back in the green pen, I spent the entire race hunting for a gap to try and overtake people. It really is running in a football crowd. The organisers have done a lot to help with the consequences of having such a large crowd. If you've got an official time from another race which gives credence to your estimated finish time, then you get to begin closer to the front. (I didn't, so I ended up in the greens, although my estimate was pretty close to the truth as it turned out.) Unfortunately, with 50, 000 entries, the start could do with being yet more staggered. Even after walking for the best part of half an hour to the start line, when you get there you're still walking.
Back in 1994 when I last did the GNR, they didn't have chip timing systems, so the only way to get an accurate time was from your own watch. At least with the chip system, you get an official time that's based on when you cross the start line as well as the finish line.
Anyway - if the organisers want to improve things yet further, here are my suggestions:

  • Disqualify people who cheat on their start colour. This could easily be done by putting a chip mat at the front of each colour zone and not giving medals to anyone who didn't cross the mat for their colour. (This also accommodates the rule that allows you to go back a colour but not forward.)
  • Make it explicit in the guidance to runners that if you are walking, or otherwise slowing down to a pace which forces others to pass you, please get over to the left and let people past. Some people were even walking three abreast after only a mile or two.

So - as stated above, my official time was 1:56:49, which gave me a position of 9690. (I guess at this point I should emphasise the 40, 000 people who came in after me!)

They were also kind enough to provide an official 10 mile split, which was 1:29:08

While running I took 5km splits. Here are the timings off my own watch:

5km 27:08 27:08
10km 28:49 54:57
15km 28:05 1:23:02
20km 29:19 1:52:21
Half marathon
5:30 1:56:51

On the 21st October, I'll be doing the Amsterdam half-marathon. That's not really far enough away to get in much extra training, but I still have hopes to come in with a faster time, if only because there'll be less of a crowd. Then again, I alwaystalked a good race. :-)

Specifying a DNS server under Gentoo linux

Posted by Dominic Cronin at Sep 23, 2007 06:05 PM |

I realised this afternoon that trackback pings from this server weren't reaching their targets. A short investigation showed that I couldn't resolve domain names. For name resolution to work, you need to have a "nameserver"  directive in  /etc/resolv.conf ,  but  there wasn't one there. I remembered that I'd solved the same problem a few months ago by adding such a directive. Obviously I hadn't been thorough enough at the time if it was now broken again.

The obvious candidate to blame was rebooting the system. I'd rebooted for some reason a few weeks ago; presumably it had been broken since then. This was indeed the case as it turned out. On a Gentoo system the /etc/resolv.conf file is created by the init scripts. These init scripts use data from /etc/conf.d/net. The problem I had was that I didn't know the correct syntax for a directive in this file which would cause resolv.conf to get a nameserver directive.

After much digging, it turned out that:

  1. There is no documentation
  2. There is a file called /etc/conf.d/net.example which contains sufficient detail to allow you to fix the problem

If you add something like this to /etc/conf.d/net :

dns_servers=( "" )

you'll end up in your /etc/resolv.conf with a line that looks like this:


Hope this helps