librope VS proposal-explicit-resource-managemen

Yep. A few years ago I implemented a skip list based rope library in C[1], and after learning rust I eventually ported it over[2].

The rust implementation was much less code than the C version. It generated a bigger assembly but it ran 20% faster or so. (I don't know why it ran faster than the C version - this was before the noalias analysis was turned on in the compiler).

Its now about 3x faster than C, thanks to some use of clever layered data structures. I could implement those optimizations in C, but I find rust easier to work with.

C has advantages, but performance is a bad reason to choose C over rust. In my experience, the runtime bounds checks it adds are remarkably cheap from a performance perspective. And its more than offset by the extra optimizations the rust compiler can do thanks to the extra knowledge the compiler has about your program. If my experience is anything to go by, naively porting C programs to rust would result in faster code a lot of the time.

And I find it easier to optimize rust code compared to C code, thanks to generics and the (excellent) crates ecosystem. If I was optimizing for runtime speed, I'd pick rust over C every time.

[1] https://github.com/josephg/librope

[2] https://github.com/josephg/jumprope-rs

> it’s not clear if this will be a positive for native dev advocacy

I've rewritten a few things in rust. Seems pretty positive to me, because you can mix some of the best optimizations and data structures you'd write in C, with much better developer ergonomics.

A few years ago I wrote a rope library in C. This is a library for making very fast, arbitrary insert & delete operations in a large string. My C code was about as fast as I could make it at the time. But recently, I took a stab at porting it to Rust to see if I could improve things. Long story short, the rust version is another ~3x faster than the C version.

https://crates.io/crates/jumprope

(Vs in C: https://github.com/josephg/librope )

The competition absolutely isn't fair. In rust, I managed to add another optimization that doesn't exist in the C code. I could add it in C, but it would have been really awkward to weave in. Possible, but awkward in an already very complex bit of C. In rust it was much easier because of the language's ergonomics. In C I'm using lots of complex memory management and I don't want to add complexity in case I add memory corruption bugs. In rust, well, the optimization was entirely safe code.

And as for other languages - I challenge anyone to even approach this level of performance in a non-native language. I'm processing ~30M edit operations per second.

But these sort of performance results probably won't scale for a broader group of programmers. I've seen rust code run slower than equivalent javascript code because the programmers, used to having a GC, just Box<>'ed everything. And all the heap allocations killed performance. If you naively port python line-by-line to rust, you can't expect to magically get 100x the performance.

Its like, if you give a top of the line Porsche to an expert driver, they can absolutely drive faster. But I'm not an expert driver, so I'll probably crash the darn thing. I'd take a simple toyota or something any day. I feel like rust is the porsche, and python is the toyota.

> I have no idea whether that matters or even easy to measure...

It is reasonably easy to measure, and the GP is about right. I've measured a crossover point of around a few hundred items too. (Though I'm sure it'll vary depending on use case and whatnot.)

I made a rope data structure a few years ago in C. Its a fancy string data structure which supports inserts and deletes of characters at arbitrary offsets. (Designed for text editors). The implementation uses a skip list (which performs similarly to a b-tree). At every node we store an array of characters. To insert or delete, we traverse the structure to find the node at the requested offset, then (usually) memmove a bunch of characters at that node.

Q: How large should that per-node array be? A small number would put more burden on the skip list structure and the allocator, and incur more cache misses. A large number will be linearly slower because of all the time spent in memmove.

Benchmarking shows the ideal number is in the ballpark of 100-200, depending on CPU and some specifics of the benchmark itself. Cache misses are extremely expensive. Storing only a single character at each node (like the SGI C++ rope structure does) makes it run several times slower. (!!)

Code: https://github.com/josephg/librope

This is the constant to change if you want to experiment yourself:

https://github.com/josephg/librope/blob/81e1938e45561b0856d4...

In my opinion, hash tables, btrees and the like in the standard library should probably swap to flat lists internally when the number of items in the collection is small. I'm surprised more libraries don't do that.

In addition to this, is the new (stage 3 even!)explicit resource management proposal[0], supported by TypeScript version >= 5.2[1]

Though I agree that async context is better fit for this generally, the RMP should be good for telemetry around objects that have defined lifetime semantics, which is a step in the right direction you can use today

[0]: https://github.com/tc39/proposal-explicit-resource-managemen...

[1]: https://www.totaltypescript.com/typescript-5-2-new-keyword-u...

There's a conversation I had with Ron Buckton, the proposal champion, mainly on this specific issue. [1]

Short answer: Yes, Disposable can leak if you forget "using" it. And it will leak if the Disposable is not guarded by advanced GC mechanisms like the FinalizationRegistry.

Unlike C# where it's relatively easier to utilize its GC to dispose undisposed resources [2], properly utilizing FinalizationRegistry to do the same thing in JavaScript is not that simple. In response to our conversation, Ron is proposing adding the use of FinalizationRegistry as a best practice note [3], but only for native handles. It's mainly meant for JS engine developers.

Most JS developers wrapping anything inside a Disposable would not go through the complexity of integrating with FinalizationRegistry, thus cannot gain the same level of memory-safety, and will leak if not "using" it.

IMO this design will cause a lot of problems, misuses and abuses. But making JS to look more like C# is on Microsoft's agenda so they are probably not going to change anything.

[1]: https://github.com/tc39/proposal-explicit-resource-managemen...

I'm not _entirely_ sure which RAII you mean, but if you mean something like C#'s `using` or Java's `try-with-resources` or Python's `with`, then https://github.com/tc39/proposal-explicit-resource-managemen... and https://github.com/tc39/proposal-async-explicit-resource-man... are in stage 3 (of 4 stages) in ECMAScript's language proposal lifecycle and will be coming to a JS engine near you behind a flag soon-ish.

I'd prefer something with a more sound type system, and something that makes cleaning up resources easier and more ergonomic.

This might help with cleanup: https://github.com/tc39/proposal-explicit-resource-managemen...

But I'm not sure anything will help with the type system. For example, this drives me absolutely insane: https://www.typescriptlang.org/play#code/MYewdgziA2CmB00QHMA...

There's a proposal for syntax to help with this in JS, incidentally: https://github.com/tc39/proposal-explicit-resource-managemen...

There is no reason why you could not, in principle, have Rust-style compile-time borrow checking in a managed language.

As an extreme example (that I have occasionally thought about doing though probably won't), you could fork TypeScript and add ownership and lifetime and inherited-mutability annotations to it, and have the compiler enforce single-ownership and shared-xor-mutable except in code that has specifically opted out of this. As with existing features of TypeScript's type system, this wouldn't affect the emitted code at all—heap allocations would still be freed nondeterministically by the tracing GC at runtime, not necessarily at the particular point in the program where they stop being used—but you'd get the maintainability benefits of not allowing unrestricted aliasing.

(Since you wouldn't have destructors, you might need to use linear instead of affine types, to ensure that programmers can't forget to call a resource object's cleanup method when they're done with it. Alternatively, you could require https://github.com/tc39/proposal-explicit-resource-managemen... to be used, once that gets added to JavaScript.)

Of course, if you design a runtime specifically to be targeted by such a language, more becomes possible. See https://without.boats/blog/revisiting-a-smaller-rust/ for one sketch of what this might look like.

Things like https://github.com/tc39/proposal-explicit-resource-managemen.... Essentially better language level support for objects which represent some IO resource that should be reliably closed when a user is done with it. Something like the `defer` statement in Go is really missing from JS.