rust VS mimalloc

async traits are in the process of being stabilized: https://github.com/rust-lang/rust/pull/115822

Also, impl trait projections (ability to use Self::Foo associated types in async functions in traits): https://github.com/rust-lang/rust/pull/115659

Rust

See for example https://github.com/rust-lang/rust/issues/63818 and https://github.com/rust-lang/rfcs/pull/3467

Basically the problem is that async blocks/fns/generators need to create a struct that holds all the local variables within them at any suspension/await/yield point. But local variables can contain references to other local variables, so there are parts of this struct that reference other parts of this struct. This creates two problems:

- once you create such self-references you can no longer move this struct. But moving a struct is safe, so you need some unsafe code that "promises" you this won't happen. `Pin` is a witness of such promise.

- in the memory model having an `&mut` reference to this struct means that it is the only way to access it. But this is no longer true for self referential structs, since there are other ways to access its contents, namely the fields corresponding to those local variables that reference other local variables. This is the problem that's still open.

Rust Programming Language

AFAIK it's just waiting on the fix in https://github.com/rust-lang/rust/pull/114489 to land, I don't know of any other blockers.

- Async traits: coming soon https://blog.rust-lang.org/inside-rust/2023/05/03/stabilizin..., actively in development (and has been for a while now, please don't confuse "this problem is hard and taking a long time" with "we don't care about this problem" https://github.com/rust-lang/rust/issues?q=is%3Aissue+label%...).

- async `Drop`: there have been multiple "false-starts", trying to come up with an acceptable design. We don't have a good answer for this at the moment. It is unknown to me how long it might take for us to figure it out.

- TAITs: same as async traits. It'll likely land after async fn in traits, but it's part of the same design and implementation effort.

- variadic generics (unlikely they will every be implemented): agree with your assessment, at least in the short to medium term.

- generic closures: same as above.

- optional/named parameters: I believe that this feature as such might never exist in rust but think that a combination of structural structs (`struct { bar: usize, baz: usize }`) and/or struct literal inference (`let x: S = _ { bar: 1, baz: 2 }`) and default const values in structs (`struct S { foo: usize = 42, bar: usize }`/`S { bar: 0, .. }`) would be more generally useful and would nicely cater to this use case (`foo(_ { bar: 42, .. }`).

- anonymous enums: I want this as well, but it interacts poorly with type parameters and automatic type upcasting (if you have `A | B` can you convert it into `A | B | C`? Does it need syntax? What about `Result<(), ()> | Option<()> | Result`? If you have a function that returns that, what does `return Err(())` do?). Type downcasting could be done by forcing a match expression on the value. Whether `A | B` should `impl T` if `A: T, B: T` is an open question. I want to push for a solution here in the coming year.

> from my totally uninformed bystander perspective, there's been a sharp drop in people working on the language and compiler full-time since around Mozilla layoffs, and Rust still hasn't recovered from that

In terms of number of commits to the rust-lang/rust repo, activity peaked in late 2019/early 2020, whereas the Mozilla layoffs took place in late 2020. Activity since late 2020 has mostly stayed stable, and remains well above where it was at any point prior to 2018: https://github.com/rust-lang/rust/graphs/contributors

In addition, I know of several former Mozillians who remain employed to work on Rust, including one who heads the Rust team at Amazon.

As far as the number of contributors to each release, it's currently hovering around an all-time average high (although a handful of past releases have anomalously high peaks): https://thanks.rust-lang.org/

Yes, it's very efficient and that's not where the main problem lies. However, small allocations with modern C heap allocators like mimalloc or snmalloc has gotten extremely efficient as well. Would be interesting to see a benchmark comparison with Java's G1 and ZGC.

Memory management for C is not itself a solved problem, not only is there a lot of performance to squeeze out of malloc itself (the benchmarks on https://github.com/microsoft/mimalloc exemplifies the variance between the implementations), but it's up to the programmer to implement memory management in the large in an efficient way, which is not an easy task. One sure mark of a slow C program is one with a ton of mallocs and frees strewn all over.

If you are fine with heap allocations then there are only few dozens operator new/delete to override to regain control over normal C++ code memory use. Allocators and STL all need to call those. At least that's what gaming does on all platforms. If you need examples you can check Mimalloc on github ( https://github.com/microsoft/mimalloc/blob/master/include/mimalloc-new-delete.h ).

What's the difference between this and Microsoft's? https://github.com/microsoft/mimalloc

This meant removing support for custom polymorphic memory resources, as clang still has no implementation for `memory_resource`. Instead, Ichor recommends using the provided mimalloc, as it tends to save on memory usage and increase performance significantly.

I know you said you’d rather avoid jemalloc or the like, but for a quick set of stats you can LD_PRELOAD something like mimalloc, and use the MIMALLOC_SHOW_STATS=1 environment variable to get some coarse grained usage stats of allocations and frees.

This doesn’t directly address your concerns, but you may be interested in trying https://github.com/microsoft/mimalloc

Version 0.1.19 of the Rust wrapper for the mimalloc memory allocator has just been released!

Has anyone used https://github.com/microsoft/mimalloc as a drop in replacement of malloc? Were there any perf improvements?