Wed 2023-02-08

Running Fexl on Windows

Every once in a while I've wondered what it would take to port Fexl to Windows. I did consider doing a completely native implementation — after all, I have written native C code on Windows before, though that was back in the late 90s. I'm not thrilled with the development environment compared to Linux, but I could probably manage something and start slogging through it.

The Linux version includes features that use all sorts of Linux system calls such as usleep, exec, dup, fopen, setrlimit, fork, dup, pipe, and many others. I would like the Windows version to behave exactly like the Linux version, or as close as possible.

Now consider just the fork and exec calls alone. I could probably port that using CreateProcess on Windows, but there could be subtle semantic differences. Then how would I replicate the behavior of all those other system calls, even approximately? For example, What is the equivalent of setrlimit, and how "equivalent" is it, really?

I did experiment with Cygwin, and it's pretty interesting. I was able to build Fexl on Windows under Cygwin, and the checks pretty much passed, with the exception of things like test/stats.fxl which call the rand function to get some weakly random numbers. I mean I do specify a fixed seed, but the generated sequence is still different because I suppose Cygwin uses different code for rand.

So it's a little sloppy under Cygwin, but oh well. Then there's the issue of getting Fexl to run outside the Cygwin terminal. They have you bind your application with a special Cygwin DLL. I never quite got that far because I had other priorities.

Today I was using a Windows machine for completely unrelated reasons and I decided to revisit the issue of porting Fexl to Windows. As I contemplated the nature of computing, I was struck with the obvious fact that a Linux machine and a Windows machine are essentially both just physical devices with patterns of electrical fields fluctuating rapidly within them. Although the hardware is virtually identical, those patterns make all the difference in their outward behavior — and in some cases, misbehavior.

All that philosophical musing suggested one solution: use a virtual machine. So I started looking at VirtualBox (in "seamless" mode) and VMware (in "unity" mode). I started going through the installation of VirtualBox, and it required C++ 2019. So I started to install Visual Studio, and as it downloaded over 3 GB of data, I perused the internet for other articles on virtual machines.

That's when I stumbled on a little product from Microsoft called "Windows Subsystem for Linux", and that's when I found a solution for porting Fexl to Windows.

WSL — Windows Subsystem for Linux

Windows Subsystem for Linux ("wsl") is a highly integrated virtual machine which supports multiple Linux style distributions running on Windows. Installing it is roughly just running this command in the Power Shell, and restarting the computer:

wsl --install

After that, you'll find a new app called "Ubuntu" which you can search in the Start menu and pin to the task bar. You bring up an Ubuntu window, and you're in bona fide Linux shell. You can use vim, you can install the gcc compiler with "apt get install" -- the works. It is Linux running on the machine.

If you have any troubles, you probably just need to "Enable Virtualization" in the BIOS, using the standard F1/F2/Del/Alt-F4/whatever trick during bootup to get to that option screen. But on my machine I found that Enable Virtualization was enabled by default.

Well then I was off to the races. I "git cloned" the Fexl code and the tests ran perfectly. I even cloned a graphics application couple of us are developing which uses Fexl to generate C code that uses the raylib library to render a 3D graphic scene.

Everything "just worked," to the point where I felt just as productive developing and testing on the Windows machine as I did on my Linux machine. At times it felt surreal, but why should it? After all, it's all the same basic hardware, it's just a matter of getting the right electrical field patterns pulsing through them. Easier said than done: this took a lot of hard and brilliant work from the people at Microsoft, and I'm grateful.

wsl.exe

So then I thought, fine, I can run these Fexl programs from within the Ubuntu window, but is there any way I could make something you could double-click from the Windows desktop, or click in the Windows start menu, that would bring up one of these programs without having to go into the Linux environment?

Well of course there is, using the little marvel called called "wsl.exe"! That is a Windows executable that can run a Linux command within a WSL virtual machine. You can run it from the ordinary Windows command prompt, or from a batch script. For example to run that graphics demo I mentioned above, I ran this from the command prompt:

wsl.exe ~/code/fexl/bin/fexl project/demo.ray/src/demo_9457.fxl

I also wrapped that up in a batch file "demo_9457.bat" so I could run it easily.

There's a lot of hot development happening on Linux these days, and I think WSL provides a seamless way to take advantage of that on Windows machines. It might even reduce the motivation for end users and even developers to switch fully to Linux. I still prefer my System76 laptop running native PopOS, but I felt right at home using Linux under Windows, courtesy of WSL.