Arnt Gulbrandsen
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2019-02-05

The young traveller's guide to Venice

Venice may quite possibly have the best-looking ambulances in the world.

It also has more of them than I'd expect for a city as small as Venice. Is it possible that the Italians keep a few extra to show off in front of young tourists?

When they're not racing stylishly through the city, the ambulances may be seen waiting in front of the hospital. The fireboats are stationed near the San Toma' bus stop, just a few meters from the grand canal, police boats are often to be seen near the Piazzale Roma and grey uniformed boats belonging to the Guardia di Finanza are at the eastern end of Giudecca. The navy may have some boats in the Arsenale, or not.

Cranes and other construction boats seem to be all over the city. A particularly impressive yellow monster has a dedicated quay just outside the Arsenale, and can be seen from the exhibition site's eastern garden or from San Pietro di Castello.

2019-01-23

static final volatile int foo = 1;

It's likely that my compiler treats foo as though it were just static final, and if you do not understand how a final volatile variable differs from a plain final, then congratulations.

The problem is that although people generally think of static final variables as constants, they aren't quite constant: foo is assigned its value early in the life of the application and can never be reassigned and, but if two or more classes reference each other, so that each class has to be initialised before the other, then code involved in that initialisation may see foo still being 0. This is usually an unpleasant surprise, found while debugging. volatile affects the visibility of the foo=1 assignment, and it probably forbids one of the things my compiler does to handle those loops.

I can fix it and I probably will, although I will not be highly motivated: It's a minor problem, and quite frankly, people whose code depends on the semantics of static final volatile ought to go for a walk in the park and reconsider that aspect of their design.

2019-01-17

I write a benchmark

Today I need to write a benchmark.

I have decided to reimplement HTML Tidy in a simple, approximate way. I chose this because:

Of course I realise that this won't be a very good as a benchmark. I chose it because I believe that Jsoup is the kind of code I need to handle well. If my code doesn't do well on Jsoup, then I need to fix it. I don't have the same feeling about specint and other well-known benchmarks. They try to be good, precise benchmarks, and they don't explicitly try to be typical java.

As a result this benchmark will be useful for me, and the cost of that is that its measured performance is imprecise for you.

2018-12-20

15000% improvement

I've been working on something that, I think, ought to perform 30%-200% better than the current solutions, depending on the workload and how the measurement mixes values for average/­typical/­best-case/­worst-case time and space. Some workloads might get more than 200% improvement, and I hope less than 30% will be rare.

The very first time I tried to measure the entire system, however, my measured result wasn't 30% improvement or 200%, it was a little over 15000%. Three zeroes. And I wasn't even trying to make a misleading benchmark — I just wanted to measure how well my code worked and I suppose I unconsciously concentrated on parts where the differences should show up clearly.

15000% certainly is a clear difference.

It's also totally meaningless. It measures something you'll never, ever do. However, it's a fantastically big number, I know that I was honest, and it has taught me that even if benchmark results are laughably unrealistic, it's not always because someone tried to brag or mislead. Maybe they are just myopic. Focused on the details of their work.

I've spoken harsh words about other people's benchmarks in the past. I don't think I will do that any more.

Update: 1500000‱.

Update: And the best way to represent it is with a logarithmic bar graph. Most people do not really understand a log scale, but the difference still looks very large and so the meaning is preserved. The label on the y axis makes it formally correct.

2018-12-11

A recipe for limoncello and marmalade

There are many limoncello recipes on the web, but so many are careless or incomplete that I add ours to the cacophony. Key points: You have to use the right kind of alcohol, you have to taste every day while you steep zest in alcohol, and the leftovers make lovely marmalade. Ingredients:

  • Alcohol (60-96%, not 40%)
  • Sugar (either white or light brown)
  • Water
  • Lemons
  • Pectin

For 1l of 96% alcohol, you should have 1-1.5kg of sugar, 2kg of lemons, and the amount of pectin depends on the lemons and your endurance. The amounts below assume 1l of 96% alcohol.

The reason that you can't start with 40% alcohol is that the end result has to contain about 32% alcohol in order to remain entirely fluid in the freezer, and the alcohol is mixed with a syrup. If the syrup is to reduce the alcohol content by only 8%, you would have to make it with just a few tablespoons of water, and you simply cannot dissolve enough sugar (more…)

2018-10-20

He's dead, but he won't lie down

Windows XP should be dead years ago, but but the number of web browsers using XP seems to not even decrease. And not at a negligible level, either, XP is used several times more than linux.

Progress is hard.

2018-10-11

Art on this blog

Art was not the purpose of this blog, but I posted a photo of a bridge and liked the result. Whenever I posted something after that, I'd see some art when I proofread what I had just posted. Until the flooded bridge was no longer on the front page and I discovered that I missed it.

So I'm going to post some pure art every year, enough that there usually is something on the front page of the blog, because art is good for the mind. Perhaps that's also why I have a painting, a reproduction, and an abstract photo in my office too, (more…)

2018-09-21

Seeing like a state

This is the third blog posting in three days. The intelligent reader may have guessed it: I'm tidying my office again. Yes I am. One desk is tidy already, and while working on the second desk, I found a book called Seeing like a state in one of the piles.

There was a note sticking out of page 352, so of course I opened the book and started reading.

The book is a strong condemnation of various well-intended reforms and schemes. Why did so-and-so agrarian reform fail? Because the reformers expected reality to match a simplistic model and when it didn't, they tried to bend reality to their model instead of the other way around. In some cases reality eventually bent (at considerable cost to the people whose lives were being reformed), (more…)