One of the big sources of difficulty on the async ecosystem is spawning tasks. Because there is no API in std for spawning tasks, library authors who want their library to spawn tasks have to depend on one of the multiple executors in the ecosystem to spawn a task, coupling the library to that executor in undesirable ways. Ideally, many of these library authors would not need to spawn tasks at all.…

Today I’m releasing a library called iou. This library provides idiomatic Rust bindings to the C library called liburing, which itself is a higher interface for interacting with the io_uring Linux kernel interface. Here are the answers to some questions I expect that may provoke. What is io_uring? io_uring is an interface added to the Linux kernel in version 5.1. Concurrent with that, the primary maintainer of that interface has also been publishing a library for interacting with it called liburing.…

The first version of async/await syntax is in the beta release, set to be shipped to stable in 1.39 on November 7, next month. There are a wide variety of additional features we could add to async/await in Rust beyond what we’re shipping in that release, but speaking for myself I know that I’d like to pump the breaks on pushing forward big ticket items in this space. Let’s let the ecosystem develop around what we have now before we start sprinting toward more big additions to the language.…

Many people who use Rust for a bit - especially those who like the language but do not fall in love with it - feel a sense that there must be a smaller, simpler variation on the same theme which would maybe be a little less powerful, but would also be much easier to use. I agree with them, but I think they are almost always wrong about what would need to change. Here are some notes on where I would start to create that smaller Rust.

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In my previous post I said that the lang team would be making our final decision about the syntax of the await operator in the May 23 meeting. That was last Thursday, and we did reach a decision. In brief, we decided to go forward with the preliminary proposal I outlined earlier: a postfix dot syntax, future.await. For more background, in addition the previous post on my blog, you can read this write up about some of the trade offs from April.…

The idea of a zero cost abstraction is very important to certain programming languages, like Rust and C++, which intend to enable users to write programs with excellent performance profiles with relatively little effort. Since this idea is fundamental to the design of Rust and my work, I want to investigate, for a moment, what exactly a zero cost abstraction even is. The idea is summarized in its original by Bjarne Stroustrup, the original developer of C++:…

This is an announcement regarding the resolution of the syntax for the await operator in Rust. This is one of the last major unresolved questions blocking the stabilization of the async/await feature, a feature which will enable many more people to write non-blocking network services in Rust. This post contains information about the timeline for the final decision, a proposal from the language team which is the most likely syntax to be adopted, and the justification for this decision.…

The biggest unresolved question regarding the async/await syntax is the final syntax for the await operator. There’s been an enormous amount of discussion on this question so far; a summary of the present status of that discussion and the positions within the language team is coming soon. Right now I want to separately focus on one question which impacts that decision but hasn’t been considered very much yet: for loops which process streams.…

This is my second post on the design of generators. In the first post, I outlined what an MVP of the feature would look like. In this post, I want to take a look at the first design issue for the feature: how it integrates with the ? operator. To explain exactly what I mean, let’s start with a specific motivating example: // This generator yields the number of alphanumeric characters in every line // in some io::Read'able data // exact sign function declaration syntax left unspecified on purpose |data| { let mut buffered_data = BufReader::new(data); let mut string = String::new(); while buffered_data.…

We’re still not finished with the design of async/await, but it’s already become clear that it’s time to get the next phases of the feature into the pipeline. There are two extensions to the minimal async/await feature we’ve currently got that seem like the clear high priority: Async methods: allowing async fn to be used in traits. Generators: allowing imperative control flow to create Iterators and Streams the same way async fn allows imperative control flow to create a Future.…