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Git implemented in Rust

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Re: Git implemented in Rust

#81

Post by Twisol »

abhijat wrote: post #76
steveklabnik wrote: post #72

Earlier quoted context omitted.

I haven’t read it yet, but I’m lucky to call the author a friend. I read all of his tweets about it while he was building it. I expect it to be of extremely high quality. I’ve got a lot of respect for his abilities. The only reason I haven’t read it yet is that I think it deserves a lot of attention and I haven’t made time yet.

Thanks, I bought the book. Still undecided as to which language to work in, I wanted to use rust but the one part I'm unsure about is possibly where tree like data structures will need to be implemented? I guess that's tough to do in rust? I will give it a try.

Graphs are harder if you try to use pointers to identify neighbors. In Rust, a pointer is not merely an index into memory; it is a statement and guarantee about how that memory will be accessed. These semantics are more than a graph structure needs.

To "get around" this (but see the next paragraph), we usually associate each node to a simple identifier such as an integer (usize), and store all nodes into a Vec. Neighbors are indexed by this identifier rather than a pointer. (Indirection? Maybe. But I'm pretty sure most processors support a base+offset mode just as easily as a direct reference mode.)

Honestly, I think this is good practice even outside of Rust. If you're using pointers, and you want to associate some extra data to a node that isn't part of its graph structure -- a label, say, or some other structure that you're modeling the relationships of -- there's no good way to add that data without modifying the definition of a node. A pointer indexes a _single_ point in memory. An abstract identifier may index any number of points in memory -- just create another table containing the new information you want to associate.

Re: Git implemented in Rust

#82

Post by steveklabnik »

abhijat wrote: post #76
steveklabnik wrote: post #72

Earlier quoted context omitted.

I haven’t read it yet, but I’m lucky to call the author a friend. I read all of his tweets about it while he was building it. I expect it to be of extremely high quality. I’ve got a lot of respect for his abilities. The only reason I haven’t read it yet is that I think it deserves a lot of attention and I haven’t made time yet.

Thanks, I bought the book. Still undecided as to which language to work in, I wanted to use rust but the one part I'm unsure about is possibly where tree like data structures will need to be implemented? I guess that's tough to do in rust? I will give it a try.

I personally like to work on one thing at a time. If you're really trying to learn about how Git works, you should, in my opinion, use a language you already know well. That way, you're focused on learning one thing, not two things at once. So I would recommend using the language that you know best.

Not everyone agrees with me, of course.

As I said, I haven't read the book yet, so I can't tell you how easy/difficult it will be in Rust. The author is learning Rust now, incidentally. But if you need a graph (which you probably will), I'd advise you to use something like https://crates.io/crates/petgraph instead of building one yourself. The difficulty is in writing graphs, not using them.

Re: Git implemented in Rust

#83

Post by jchw »

mises wrote: post #68

Can somebody tell me what is behind the recent rewrite-all-the-things-in-rust craze? I get it can have some benefits in terms of security, but it seems rewriting so many things in it just for the sake of it is a bit excessive. I understand some of these are very likely for educational purposes (like this one and others; it's good for getting more familiar with the language), but it still seems to be a bit of a strang…

I scrolled down for this comment.

Actually there's a lot of great reasons to rewrite everything in every language. Git is an especially good piece of software to implement everywhere because it's relatively stable and it's pretty useful.

As for actual reasons, one good example is so you can keep your dependencies in the language, using the language package manager. For Go nobody even questions that this is worth it; it enables painless cross compiling and completely static, libc-free binaries. For Rust that may not be a thing, but you do at least get the benefits that you could integrate Git functionality without having to hack around in porcelain.

This one here is a learning experience by it's own description, but I would suggest people stop complaining about "rewriting everything" in $LANGUAGE. The opposite complaint is often cited as a reason why to not use the language (that, for example, basic programs haven't already been ported.) If we did build an alternate world with feature parity, unit testing, optimizations, in a memory safe language, I doubt many people would be complaining about the strange trend of rewriting things anymore.

Re: Git implemented in Rust

#84

Post by mises »

jchw wrote: post #83
mises wrote: post #68

Can somebody tell me what is behind the recent rewrite-all-the-things-in-rust craze? I get it can have some benefits in terms of security, but it seems rewriting so many things in it just for the sake of it is a bit excessive. I understand some of these are very likely for educational purposes (like this one and others; it's good for getting more familiar with the language), but it still seems to be a bit of a strang…

I scrolled down for this comment. Actually there's a lot of great reasons to rewrite everything in every language. Git is an especially good piece of software to implement everywhere because it's relatively stable and it's pretty useful. As for actual reasons, one good example is so you can keep your dependencies in the language, using the language package manager. For Go nobody even questions that this is worth it;…

That's a good point; you're right that it's helpful to be able to interface with such a ubiquitous program natively in a language of choice. I did see a mention on the page of deploying as a crate and using in another program; that seems very convenient.

> stop complaining

Not a complaint; more a question as to why there's a specific move around rust. I appreciate the reply; that's exactly the kind of response I was looking for.

Re: Git implemented in Rust

#85

Post by swsieber »

jchw wrote: post #83
mises wrote: post #68

Can somebody tell me what is behind the recent rewrite-all-the-things-in-rust craze? I get it can have some benefits in terms of security, but it seems rewriting so many things in it just for the sake of it is a bit excessive. I understand some of these are very likely for educational purposes (like this one and others; it's good for getting more familiar with the language), but it still seems to be a bit of a strang…

I scrolled down for this comment. Actually there's a lot of great reasons to rewrite everything in every language. Git is an especially good piece of software to implement everywhere because it's relatively stable and it's pretty useful. As for actual reasons, one good example is so you can keep your dependencies in the language, using the language package manager. For Go nobody even questions that this is worth it;…

There are bindings to git in Rust (https://github.com/rust-lang/git2-rs ) - I've used it in a couple of my projects (https://github.com/samsieber/subgit-sync for example).

That said, even when using those bindings, I've had to drop down to wrapping the porcelain sometimes. I'd love to have a native rust git implementation. It'd be easier to hack on, and to abuse for the type of git interactions I've written.

And it'd be one less external dependency to worry about when cross-compiling. I love how easy it is to install things from source in Rust - and it's pretty easy to add flag to make the program use your CPU's special instruction set to make it even faster.

Re: Git implemented in Rust

#87

Post by aidenn0 »

_bxg1 wrote: post #86

Rust seems like a good language for git given its performance and memory-safety, no?

Actually any high performance GC'd languages would be fine too because latency is a non-issue for long running git operations (you won't notice if your git clone pauses for 100ms, whereas you will notice if your UI does). Throughput of malloc() and GCd languages tends to be similar when latency isn't a concern.

Re: Git implemented in Rust

#88

Post by jchw »

mises wrote: post #84
jchw wrote: post #83

Earlier quoted context omitted.

I scrolled down for this comment. Actually there's a lot of great reasons to rewrite everything in every language. Git is an especially good piece of software to implement everywhere because it's relatively stable and it's pretty useful. As for actual reasons, one good example is so you can keep your dependencies in the language, using the language package manager. For Go nobody even questions that this is worth it;…

That's a good point; you're right that it's helpful to be able to interface with such a ubiquitous program natively in a language of choice. I did see a mention on the page of deploying as a crate and using in another program; that seems very convenient. > stop complaining Not a complaint; more a question as to why there's a specific move around rust. I appreciate the reply; that's exactly the kind of response I was…

Fair enough. There's definitely a lot of folks who do get upset over this stuff, maybe as pushback to the new language hype.

Re: Git implemented in Rust

#89

Post by sreque »

aidenn0 wrote: post #87
_bxg1 wrote: post #86

Rust seems like a good language for git given its performance and memory-safety, no?

Actually any high performance GC'd languages would be fine too because latency is a non-issue for long running git operations (you won't notice if your git clone pauses for 100ms, whereas you will notice if your UI does). Throughput of malloc() and GCd languages tends to be similar when latency isn't a concern.

GC is only part of the equation. I have always found this article informative: https://marc.info/?l=git&m=124111702609723&w=2

Performance for higher-level languages is usually great in-so-far as you're able to essentially write C code in that higher level language. When the language's limitations inhibit you from writing the C code you want to write, performance usually suffers. In java's case, lack of value types and stack allocation can be a major performance hindrance. Boxing is also a problem, although, as the mailing list post notes, this is easily overcome-able via manual specialization.

Re: Git implemented in Rust

#90

Post by _bxg1 »

aidenn0 wrote: post #87
_bxg1 wrote: post #86

Rust seems like a good language for git given its performance and memory-safety, no?

Actually any high performance GC'd languages would be fine too because latency is a non-issue for long running git operations (you won't notice if your git clone pauses for 100ms, whereas you will notice if your UI does). Throughput of malloc() and GCd languages tends to be similar when latency isn't a concern.

I was speaking more to stability. Rust is designed to be an incredibly safe language without sacrificing any performance; that seems like a good match for a version-control system.
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