Approaches to Resource Disposal

I’m working on developing a novel programming language, working title ‘aevum’. As part of that process, I’ll be writing a series of articles about various aspects of language design and development.

Every long running computer program is going to need to obtain a variety of resources, and those resources are almost always finite. Memory, file handles, threads, GPU resources – all of these are relatively scarce, and exhausting the available supply will have dire consequences, anywhere from killing the program, to crashing the computer on which it runs.

Given this scarcity, it is essential that we can dispose of these resources as soon as we are finished using them (or at least, before they are needed elsewhere). Although that sounds simple enough, it turns out that there are a couple of hurdles to overcome.

The first hurdle relates to ownership. As long as every resource is owned exactly once (i.e. a member variable of one object, or a local variable to one function), then disposal is trivial – a resource is disposed of as soon as it’s parent is disposed of. But requiring single ownership of every object comes with disadvantages of its own: with strict single ownership you can’t easily maintain cyclic data structures such as bi-directional lists, graphs or trees.

On the other hand, if you elect to allow multiple ownership, you are then faced with the problem of how to determine when a resource is actually no longer being used. Obviously you can’t dispose of it as long as even a single owner still exists, but how do you determine that the last owner is gone? You can explicitly keep track of the list of owners for each resource (a la reference counting), at the expense of both storage and performance, or you can at regular intervals scan the entire system to determine objects without owners (a la tracing garbage collectors), at the cost of determinism and performance.

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Fun with commas

This thread over at GameDev got me thinking, “can one assign Python-like tuples in C++?”

I don’t want to pollute the thread in For Beginners with that discussion, but the answer is yes, even without C++11 initialiser lists:

#include <iostream>

struct A {
    A &operator = (int i) {
        std::cout << "A = " << i << std::flush;

        return *this;

    A &operator , (int i) {
        std::cout << ", " << i << std::flush;

        return *this;

int main() {
    A a;

    a = 10, 20, 30;

    std::cout << std::endl;

Should you ever do this? Probably not. Though I’m guessing one of Boost’s container libraries is doing exactly this.

The price of progress

I recently installed the beta of Microsoft Office 2010, and the first thing that struck me is how it performs noticeably worse on my 3.0 GHz quad-core AMD gaming rig, than Office ’98 performed on a now 12-year-old PowerBook G3, powered by a little 250 MHz PPC processor.

You can probably guess the next stage of this little anecdote… Office ’98 on that G3 performed ever-so-slightly worse than Office 4.0 on a truly antediluvian PowerBook 180, which sported a fantastic (for the time) 33 MHz Motorola 68030 CPU.

Now, I am not being entirely fair here – the spellchecker is much faster, the grammar checker didn’t even exist back then, and various other ancillary features have been added and improved. But the core issue remains, Office 2010 (or 2007, which is not in beta) running on a very decent gaming rig, takes longer to launch and is less responsive to keyboard input than Office 4.0 on an 33 MHz 68k.

And the problem isn’t restricted to Microsoft products alone, as many pieces of software have suffered the same sort of creep, not least among them the Mac and Windows operating systems.

In the open-source world and among smaller developers this phenomenon is far less common: a well configured linux or BSD installation boots in a handful of seconds, Blender (sporting most of the features of expensive software such as 3DS Max and Maya) launches immediately and always remains responsive, and Maxis’ Spore takes minutes to start up and load a game while Eskil’s Love throws you into the game in under 10 seconds.

My current computer is many thousands of times faster than that PowerBook 180, so in theory at least, we should be able to do far more, and do the same old things much faster. Why then the slowdown?

It can’t be lack of resources – we are talking about companies such as Microsoft, Apple and Adobe, all with enormous R&D and development budgets, and teams of experienced programmers and engineers. Besides, the open-source guys manage just fine, some with just a handful of programmers, and most with no budget whatsoever.

It has been argued that programmer laziness (a.k.a. badly educated programmers) are to blame, but I am not sure this can be the entire story. Certainly the ‘dumbing down’ of University-taught computer science hasn’t helped, nor has the widespread rise of languages that ‘protect’ the programmer from the hardware, nor the rise of programming paradigms that seek to abstract away from low-level knowledge. But that is the topic of another rant, and is somewhat tangential to the topic at hand. Companies can afford to hire the best programmers, and could if they wanted to, create the demand necessary to reform education practices.

And that brings us to the real heart of the issue: software developers measure success in terms of sales and profit. As long as your software sells, there is no need to spend money on making the software perform better. And if you happen to have a virtual monopoly, such as Microsoft’s Office or Adobe’s Photoshop, then there is no incentive to improve the customer’s experience, beyond what is needed to sell them a new version each year.

However, when you lose such a monopoly, the game changes, and it generally changes for the better. When FireFox, Opera and later Safari started cutting a swathe into Microsoft’s Internet Explorer monopoly, Microsoft was forced to adapt. The latest version of Internet Explorer is fast, standards compliant, and relatively free of the virus infection risks that plagued earlier versions.

This outcome of the browser war has led at least a few to the conclusion that open-source is the answer, and that open-source will inevitably recreate what has been developed commercially, and either surpass that commercial product, or force it to evolve. Sadly, I don’t see this happening particularly quickly, or on a wide scale – OpenOffice is playing catch-up in its efforts to provide an out-of-the-box replacement for Microsoft Office, GIMP lags far behind Photoshop, and linux, despite widespread adoption in a few key fields (namely budget servers and embedded devices) still lags far behind Windows and Mac in many areas.

For many years this wasn’t a problem – every few years you would buy a new computer, typically an order of magnitude faster than the computer it replaced. If new versions of your software consumed a few million more cycles, well, there were cycles to burn, and besides, the hardware companies needed a market for faster computers, didn’t they?

Nowadays the pendulum is swinging in the opposite direction. Atom powered netbooks, Tegra powered tablets, ARM powered smartphones – all of these promise a full computing experience in tiny packages with minimal power consumption. Even though the iPhone in your hand is considerably more powerful than that 33 MHz PowerBook 180, it doesn’t have even a fraction of the computing power offered by your shiny new laptop or desktop. And users expect a lot more than they did in the early nineties – animated full colour user interfaces, high definition streaming video and flash applications, oh, and don’t drain the battery!

CPU cycles today are becoming as precious as they ever were, only now many of our programmers have no experience of squeezing every last drop of performance out of them. Has the business of software development come full circle, and once again become the territory of the elite ‘low-level’ programmer?

Community News

Various things have been snowballing recently, with the result that both development and blogging have fallen by the wayside. A few interesting things are happening however, take a look and see for yourself, after the jump…

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Simplui 1.0.2 released – now with themes!

The default themes provided by simplui

The default themes provided by simplui

Today brings the 1.0.2 release of simplui. This is a beta release, previewing major enhancements, and I need as much feedback as possible on the new features. As such, this release isn’t heavily optimised – that is on the wishlist for next release.

The big news for this release is themes support. The GUI is now fully skinned, using a variant on the ninepatch method code developed by Joe Wreschnig and Alex Holkner on the pyglet mailing list.

Each GUI frame can use a different theme (even in the same time!), and the theme can be changed at runtime. I have included two sample themes, one modelled on the Mac OS X ‘Aqua’ interface, and the other on the PyWidget GUI toolkit.

Also included are the usual crop of bug-fixes, including the squashing (hopefully for the last time) of the persistent event clipping bug.

As per usual, grab the tarball, or visit SVN, and let me know if you have any comments or suggestions.

Starfall: planet rendering

I just posted a quick youtube video to demonstrate the current state of the planet renderer. This is early development stuff, and the eye candy is minimal, but it should give you some idea of the scope.

I will follow up with a more technical blog post in the next few days, explaining all that is going on behind the scenes, and can’t be seen in a video.

Part of the rationale behind this video is to stremline the whole video capture and posting process. Unfortunately, it hasn’t been entirely straightforward so far. I went through a number of video capture tools before settling on FRAPS, which works well enough (though I would have prefered a free tool).

I also have had a terrible time converting the video for youtube – ATI’s Avivo video converter is blazingly fast, but apparently produces an incompatibe audio codec in any of the high-quality settings. I was forced to fall back to the CPU-based Auto Gordian Knot, which both does a worse job, is very slow on my little Athalon 64 x2.

I am now experimenting with ffmpeg, but the command line options are confusing to say the least. If anyone has any clues/tips/tricks for getting FRAPS encoded video (and audio) into a suitable format for youtube HD, please let me know.

simplui 1.0.1 released

I am going to be performing a number of small releases for simplui over the next few weeks, as features are added and bugs are patched.

Today’s 1.0.1 release introduces a slider control, docstrings for all widget constructors detailing the keyword arguments, and a couple of bug fixes.

You can grab the release tarball, or check out the code directly from SVN.

If anyone feels like taking it for a spin, I could do with bug reports and feedback on the API.

simplui v1.0 released

A quick demo of simplui's controls and capabilities.

A quick demo of simplui's controls and capabilities.

I like pyglet a lot. Much more than a lot.

However, the lack of a compelling GUI toolkit for development purposes has been a major irritation of late. This week I finally sat down and wrote my own GUI toolkit, from scratch, and I am happy enough with the way it works to release a first version to the public.

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