The State of Rust 0.9

Rust is a systems language pursuing the trifecta: safe, concurrent, and fast. This is my post-mortem of the past 3 months, the current status of Rust, and its future.


The compiler saw a fair bit of work this release cycle. Some polish has gone into mut in patterns. For example, let (mut x, y) = foo(); now works as expected. We now have “feature gates”, or feature flags, that let us mark certain features as either deprecated or experimental and subject to change. @mut has been removed. Slice representation has been optimized (we now store number of elements, not number of bytes). Soundness bugs have been fixed, and some bugs in our name resolution have been patched up. We have a dead code warning, stability annotations, crate introspection, and lots more.

On top of all that, we also have support for static linking and LTO. Compiler performance has further improved. From the 112ms compiling fn main() { } in 0.8, we now do 91ms with static linking (the default) and 68ms for dynamic linking (-Z prefer-dynamic). Our debuginfo is in a much better state. The entire codebase (compiler + standard library + tools) compiles with it, and Servo compiles with it by default.


The runtime has seen tons of work this release. std::io has been swapped over to the new runtime, which is written entirely in Rust. We now support both 1:1 and M:N threading models, their respective runtimes supplied by “libnative” and “libgreen”. libgreen (the “old new runtime”) has seen some performance improvements. Chris Morgan reports that the scalability of his rust-http benchmarks has improved from 1.25x to 1.75x from 1 to 8 concurrent request handlers. On my machine, using libnative gives an impressive performance boost, pushing us ahead of go’s performance (graph below). libnative has yet to see any optimization work. David Renshaw reports roughly a 2x performance increase on his capn proto benchmark when using libnative for I/O.

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<p>(This would be interactive if you had JavaScript enabled)</p>

You can run the benchmarks yourself. cd comparisons; python You’ll need to build rust-http first (make), and have go, nodejs, and ab (apache bench) installed.


Our documentation hasn’t been in the best state in the past. It still isn’t where it should be, but they have been reorganized, on top of seeing the usual work. We’re in the process of moving all of the documentation from the wiki onto that site, to make it easier to find and search. Steve Klabnik gave a critical but very constructive presentation at the Bay Area meetup about what we are doing wrong and how we can improve. At the same meetup, Chris Morgan talked about the technologies we use in our documentation stack. In the long run, the consensus seems to be that reStructuredText and Sphinx are they way forward. Thanks to the rustdoc rewrite, it will be able to have first-class status as a documentation backend.

The Future

For 0.10, we have Dynamically Sized Types (DST) to look forward to, as well as the removal of @ pointers. box, aka “placement new”, along with smart pointer sugar (overloadable dereferencing/borrowing), should also be in by then. We may also see an actual garbage collector.

Is Rust Ready Yet?

Nope. It still has some work to do. 1.0 is estimated before the end of 2014, though that may slip depending on how things land. An early estimate puts the release over the summer! We still need a robust package manager. We now have rust-ci, which makes it easy to keep code up to date, and know if a library is up to date.

The breaking changes, especially language changes, are slowing down, besides bug fixes. The standard library is also starting to shake itself out, though it still has a lot of work before they will be stable. There are currently two known uses of Rust in production: Tilde is using it in Skylight, and OpenDNS is using it for real-time data processing.

It has been a good release, and the next will be even better. Want to get involved? We love contributions. Want to follow development? I post a weekly newsletter summarizing the important changes. There is also a subreddit. Here’s to an awesome 0.10!