OS APIs: Windows 8/WinRT and GNOME/GTK+

If one is making an operating system, clearly the API that application authors use is extremely important. The whole point of an operating system is to run them. What I want to talk about is fundamental APIs, or the lowest stable level.

If you have even a passing awareness of the evolution of Microsoft Windows over the last 25 years, you know there have been a lot of APIs that have appeared, been promoted and marketed to Windows developers, and then either deprecated or relegated to just an “option”. For example, MFC. However, these APIs are all wrappers. The only time the fundamental Windows API broke incompatibly (I believe) that 16 bit applications don’t run on 64 bit; see X86-64. But the point here is that since the introduction of 32 bit Windows NT in 1993, if you coded to that API, your application will still run. If your application still runs, that means it’s the same operating system.

More recently, Microsoft for a while was promoting .NET heavily, arguably more than any of their frameworks before. It’s important to understand that at its introduction, .NET was still fundamentally a wrapper. For a while, there were rumors that it might become a fundamental API, but with the introduction of Windows 8, that won’t happen. For a really great read on this, see this ArsTechnica article. Especially fun to read are the bits about the politics, which the article only mentions in passing – you can find more scattered about the internet, like here.

Now Microsoft is saying something huge: all new APIs will be based on this new WinRT thing. Your old Win32 apps won’t break, but this time we have reason to believe they’re pretty serious – this really is the new fundamental API, and if you want your app to use new features, you will have to use WinRT. You can access WinRT from plain bog standard C, even if it’s not beautiful.

How does all of this relate to GNOME and GTK+? I think WinRT validates where we’ve been doing in GNOME with GObject Introspection. GObject may not be the most concise thing in the world (though it definitely beats C/COM), but the combination of a pure C base with added metadata and runtime support mean that all of our fundamental APIs (basically the GTK+ stack, and notably GIO for non-GUI programs) remain accessible to C and also available in other runtimes and languages.

There’s a lot more to do on introspection – we desperately need a complete documentation generator for example. It’s also pretty clear to me in that in order to truly succeed, we need to “downgrade” C to be a consumer of the API rather than a source, i.e. we need to do what Microsoft has done and define interfaces in an IDL. That will be interesting to do while still keeping around the old C APIs that don’t match the projected C binding.

TL;DR – I believe GNOME’s approach of using C with metadata and minimal runtime hooks as a fundamental operating system API is the right course, and we should keep doing what we’re doing.

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