• 4 Posts
  • 38 Comments
Joined 1 year ago
cake
Cake day: August 10th, 2023

help-circle





  • Sure, but my point was that such a C ABI is a pain. There are some crates that help:

    • Rust-C++: cxx and autocxx
    • Rust-Rust: stabby or abi_stable

    But without those and just plain bindgen it is a pain to transfer any types that can’t easily just be repr(C), and there are quite a few such types. Enums with data for example. Or anything using the built in collections (HashMap, etc) or any other complex type you don’t have direct control over yourself.

    So my point still stands. FFI with just bindgen/cbindgen is a pain, and lack of stable ABI means you need to use FFI between rust and rust (when loading dynamically).

    In fact FFI is a pain in most languages (apart from C itself where it is business as usual… oh wait that is the same as pain, never mind) since you are limited to the lowest common denominator for types except in a few specific cases.


  • Yes, rust is that much of a pain in this case, since you can only safely pass plain C compatible types across the plugin boundary.

    One reason is that rust doesn’t have stable layouts of structs and enums, the compiler is free to optimise the to avoid padding by reordering, decide which parts to use as niches for Options etc. And yes, that changes every now and then as the devs come up with new optimisations. I think it changes most recently last summer.


  • So there is a couple of options for plugins in Rust (and I haven’t tried any of them, yet):

    • Wasm, supposedly https://extism.org/ makes this less painful.
    • libloading + C ABI
    • One of the two stable ABI crates (stabby or abi_stable) + libloading
    • If you want to build them into your code base but not have to update a central list there is linkme and inventory.
    • An embedded scripting language might also be a (very different) option. Something like mlua, rhai or rune.

    I don’t know if any of these suit your needs, but at least you now have some things to investigate further.



  • I have read it, it is a very good book, and the memory ordering and atomics sections are also applicable to C and C++ since all of these languages use the same memory ordering model.

    Can strongly recommend it if you want to do any low level concurrency (which I do in my C++ day job). I recommended it to my colleagues too whenever they had occasion to look at such code.

    I do wish there was a bit more on more obscure and advanced patterns though. Things like RCU, seqlocks etc basically get an honorable mention in chapter 10.


  • Yes, Sweden really screwed up the first attempt at switching to Gregorian calendar. But there were also multiple countries who switched back and forth a couple of times. Or Switzerland where each administrative region switched separately.

    But I think we in Sweden still “win” for worst screw up. Also, there is no good way to handle these dates without specific reference to precise location and which calender they refer to (timestamps will be ambiguous when switching back to Julian calendar).








  • Two tips that work for me:

    • After cargo add I have to sometimes run the “restart rust-analyzer” command from the vscode command pallette (exact wording may be off, I’m on my phone as of writing this comment). Much faster than cargo build.
    • Consider using sccache to speed up rebuilds. It helps a lot, though uses a bit of disk space. But disk space is cheap nowadays (as long as you aren’t stuck with a laptop with soldered SSD, in which case you know what not to buy next time).



  • I don’t feel like rust compile times are that bad, but I’m coming from C++ where the compile times are similar or even worse. (With gcc at work a full debug build takes 40 minutes, with clang it is down to about 17.)

    Rust isn’t an interpreted or byte code compiled language, and as such it is hard to compete with that. But that is comparing apples and oranges really. Better to compare with other languages that compile to machine code. C and C++ comes to mind, though there are of course others that I have less experience with (Fortran, Ada, Haskell, Go, Zig, …). Rust is on par with or faster than C++ but much slower than C for sure. Both rust and C++ have way more features than C, so this is to be expected. And of course it also depends on what you do in your code (template heavy C++ is much slower to compile than C-like C++, similarly in Rust it depends on what you use).

    That said: should we still strive to optimise the build times? Yes, of course. But please put the situation into the proper perspective and don’t compare to Python (there was a quote by a python developer in the article).