Rio: an experimental and minimal runtime

If you are a fan of TV series I think you already got the analogy between a runtime called rio and the async rust. If not, you may need to take some time to see the popular TV series Money Heist ๐Ÿ˜†

However, I will spoil it, Rio a name a character in the tv series that is fall in love with another character that it is called Tokio (you got the analogy, right?), in the async rust there is a popular runtime called Tokio and I named my experimental runtime Rio because Rio in the TV Serie is a Computer science Nerd and falls in love with Tokyo that was a completely different person from him.

In fact, my Rio runtime has a dream, to use all the new features of the rust compiler regarding async programming to be a minimal portable runtime, instead, Tokio runtime is a little bit more limited on this side, in fact if you run with Rio runtime a code depending on Tokio API you will see the following stack trace

thread 'main' panicked at 'there is no reactor running, must be called from the context of Tokio runtime'

In fact, tokio API work only with the Tokio runtime.

However, I decided to start writing Rio not because I would like to solve the async runtime fragmentation problem in Rust (well, maybe yes who knows ๐Ÿ˜†), but because I was new to the async programming concept, and it was a place challenged enough to contribute to that attract me.

In fact, the proposal to write a small runtime is not from me, but from one of the team member of the rust compiler @eholk that is a great source of inspiration for me, and a source of learning.

In conclusion, Rio is born as a hello async world async runtime with a big aspiration that is to begin an experimental runtime for rust ecosystem - where you can find the more recent proposal implemented as crates.

Rio overview

Rio is available on GitHub at https://github.com/vincenzopalazzo/rio and the architecture is divided into different sub crates, that are:

  • rio_rt: Rio minimal async Runtime;
  • rio_io: Rio async IO from async IO portability proposal (in progress)
  • rio_lib: Rio experimental standard library (in progress)

Rio Design and Examples

The Rio API is really minimal, it contains just three procedure call, block_on and spawn and the most important is wait which allow waiting for the async execution to terminate.

A daily example can be the following code

use log::{debug, info};
use rio_rt::runitime as rio;
use surf;
pub(crate) mod extractor;
mod github;
use extractor::Extractor;
async fn run(extractor: &impl extractor::Extractor<Output = String>) -> Result<(), surf::Error> {
let content = extractor.search_new().await?;
info!("{}", content);
fn main() {
debug!("Here we go, we are all good");
let github = github::GithubExtractor::new();
rio::block_on(async move {

A complete example can be found at the following link

Rio into the Future

The future of rio is for sure experimental, but we also try to be a real runtime where people can rely on to build real software but at the same time keep the code base simple and easy to understand just a hello world application.

In conclusion, see Build Rio from scratch to know how to implement your own async runtime in rust, and to understand what are the challenges around the async rust.

If you find interested in this blog post please consider sponsoring me through Github Sponsor, this will help me to keep able to work with the async-wg and help in improving the async programming in rust.


Thanks to @eholk to review my blog post and give some feedback about the blog (he did not understand the analogy between rio and tokio, maybe it was not so funny :โ€™) )

In addition, the whorl was a great source of inspiration.