ractor

A pure-Rust actor framework. Inspired from Erlang's gen_server, with the speed + performance of Rust!

About

ractor tries to solve the problem of building and maintaing an Erlang-like actor framework in Rust. It gives a set of generic primitives and helps automate the supervision tree and management of our actors along with the traditional actor message processing logic. It's built heavily on tokio which is a hard requirement for ractor.

ractor is a modern actor framework written in 100% rust with NO unsafe code.

Why ractor?

There are other actor frameworks written in Rust (Actix, riker, or just actors in Tokio) plus a whole list compiled on this Reddit post

Ractor tries to be different my modelling more on a pure Erlang gen_server. This means that each actor can also simply be a supervisor to other actors with no additional cost (simply link them together!). Additionally we're aiming to maintain close logic with Erlang's patterns, as they work quite well and are well utilized in the industry.

Additionally we wrote ractor without building on some kind of "Runtime" or "System" which needs to be spawned. Actors can be run independently, in conjunction with other basic tokio runtimes with little additional overhead.

We currently have full support for

1. Single-threaded message processing
2. Actor supervision tree
3. Remote procedure calls to actors
4. Timers

On our roadmap is to add more of the Erlang functionality including potentially a distributed actor cluster.

Installation

Install ractor by adding the following to your Cargo.toml dependencies

toml [dependencies] ractor = "0.1"

Working with Actors

Actors in ractor are very lightweight and can be treated as thread-safe. Each actor will only call one of it's handler functions at a time, and they will never be executed in parallel. Following the actor model leads to microservices with well-defined state and processing logic.

An example ping-pong actor might be the following

```rust use ractor::{Actor, ActorCell, ActorHandler};

/// [PingPong] is a basic actor that will print /// ping..pong.. repeatedly until some exit /// condition is met (a counter hits 10). Then /// it will exit pub struct PingPong;

/// This is the types of message [PingPong] supports

[derive(Debug, Clone)]

pub enum Message { Ping, Pong, }

impl Message { // retrieve the next message in the sequence fn next(&self) -> Self { match self { Self::Ping => Self::Pong, Self::Pong => Self::Ping, } } // print out this message fn print(&self) { match self { Self::Ping => print!("ping.."), Self::Pong => print!("pong.."), } } }

// the implementation of our actor's "logic"

[asynctrait::asynctrait]

impl ActorHandler for PingPong { // An actor has a message type type Msg = Message; // and (optionally) internal state type State = u8;

// Initially we need to create our state, and potentially
// start some internal processing (by posting a message for
// example)
async fn pre_start(&self, myself: ActorCell) -> Self::State {
    // startup the event processing
    self.send_message(myself, Message::Ping).unwrap();
    0u8
}

// This is our main message handler
async fn handle(
    &self,
    myself: ActorCell,
    message: Self::Msg,
    state: &Self::State,
) -> Option<Self::State> {
    if *state < 10u8 {
        message.print();
        self.send_message(myself, message.next()).unwrap();
        Some(*state + 1)
    } else {
        myself.stop(None);
        // don't send another message, rather stop the agent after 10 iterations
        None
    }
}

}

[tokio::main]

async fn main() { let (, actorhandle) = Actor::spawn(None, PingPong).await.expect("Failed to start actor"); actor_handle.await.expect("Actor failed to exit cleanly"); } ```

which will output

bash $ cargo run ping..pong..ping..pong..ping..pong..ping..pong..ping..pong.. $

Messaging actors

The means of communication between actors is that they pass messages to each other. A developer can define any message type which is Send + 'static and it will be supported by ractor. There are 4 concurrent message types, which are listened to in priority. They are

1. Signals: Signals are the highest-priority of all and will interrupt the actor wherever processing currently is (this includes terminating async work). There is only 1 signal today, which is Signal::Kill, and it immediately terminates all work. This includes message processing or supervision event processing.
2. Stop: There is also a pre-defined stop signal. You can give a "stop reason" if you want, but it's optional. Stop is a graceful exit, meaning currently executing async work will complete, and on the next message processing iteration Stop will take prioritity over future supervision events or regular messages. It will not terminate currently executing work, regardless of the provided reason.
3. SupervisionEvent: Supervision events are messages from child actors to their supervisors in the event of their startup, death, and/or unhandled panic. Supervision events are how an actor's supervisor(s) are notified of events of their children and can handle lifetime events for them.
4. Messages: Regular, user-defined, messages are the last channel of communication to actors. They are the lowest priority of the 4 message types and denote general actor work. The first 3 messages types (signals, stop, supervision) are generally quiet unless it's a lifecycle event for the actor, but this channel is the "work" channel doing what your actor wants to do!

Contributors

The original authors of ractor are Sean Lawlor (@slawlor), Dillon George (@dillonrg), and Evan Au (@afterdusk). To learn more about contributing to ractor please see CONTRIBUTING.md

License

This project is licensed under MIT.