It is great that Fil-C exists. This is the sort of technique that is very effective for real programs, but that developers are convinced does not work. Existence proofs cut through long circular arguments.
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Some programs have a ~4x slowdown. That's also not super common, but it happens.
Most programs are somewhere in the middle.
> for the use-cases where C/C++ are still popular
This is a myth. 99% of the C/C++ code you are using right now is not perf sensitive. It's written in C or C++ because:
- That's what it was originally written in and nobody bothered to write a better version in any other language.
- The code depends on a C/C++ library and there doesn't exist a high quality binding for that library in any other language, which forces the dev to write code in C/C++.
- C/C++ provides the best level of abstraction (memory and syscalls) for the use case.
Great examples are things like shells and text editors, where the syscalls you want to use are exposed at the highest level of fidelity in libc and if you wrote your code in any other language you'd be constrained by that language's library's limited (and perpetually outdated) view of those syscalls.
That actually brings up another question: how would trying to run a JIT like V8 inside Fil-C go? I assume there would have to be some bypass/exit before jumping to generated code - would there need to be other adjustments?
I’ll admit that if you are in the business of counting instructions then other things in Fil-C will kill you. Most of the overhead is from pointer chasing.
Sure, though this is also true for ordinary serial code, with all the intricate interactions between the OS scheduler, different caches, filesystem, networking, etc.
Those are the environments that John upthread was talking about when he said:
> There's tons of embedded use cases where a GC is not going to fly just from a code size perspective, let alone latency. That's mostly where I've often seen C (not C++) for new programs.
But I've seen C++ there too.
If you're worried about the code size of a GC you probably don't have a filesystem.
But I don't really think it's meaningful to bring that up as it is a niche of a niche. Soft-real time (which most people may end up touching, e.g. video games) are much more forgiving, see all the games running on Unity with a GC. An occasional frame drop won't cause an explosion here, and managed languages are more than fine.
I don't agree that "it is a niche of a niche". There are probably 32× as many computers in your house running hard-real-time software as computers that aren't. Even Linux used to disable interrupts during IDE disk accesses!
Meh. I was in the real time GC game for a while, when I was younger. Nobody agrees on what it really means to bound the worst case. If you're a flight software engineer, it means one thing. If you're a game developer, it means something else entirely. And if you're working on the audio stack specifically, it means yet another thing (somewhere in between game and flight).
So let me put it this way, using the game-audio-flight framework:
- Games: I bound worst case execution time, just assuming a fair enough OS scheduler, even on uniprocessor.
- Audio: I bound worst case execution time if you have multiple cores.
- Flight: I don't bound worst case execution time. Your plane crashes and everyone is dead
I say that even though, as you noticed in another reply, I worked on research to try to make GC suitable for exactly those environments. I had some cool demos, and a lot of ideas in FUGC come from that. But I would not recommend you use GC in those environments!
There is a way to engineer Fil-C to not rely on GC. InvisiCaps would work with isoheaps (what those embedded dudes would just call "object pools"). So, if we wanted to make a Fil-C-for-flight-software then that's what it would look like, and honestly it might even be super cool