swactor/src/lib.rs

pub mod error;

use std::{
    marker::PhantomData,
    sync::{Mutex, mpsc::TryRecvError},
};

use crate::error::{Error, Result, convert_err};

use std::sync::mpsc;

use bytemuck::{Pod, Zeroable};

#[repr(C)]
#[derive(Copy, Clone, Pod, Zeroable)]
struct GreeterState {
    pub num_greeted: usize,
}

enum GreetMessage {
    Name(String),
}

enum GreetResponse {
    Greeting(String),
}

type GreeterId = u64;

struct Greeter {
    id: GreeterId,
    inbox: mpsc::Receiver<GreetMessage>,
    outbox: mpsc::Sender<GreetResponse>,
    state: GreeterState,
}

impl Greeter {
    pub fn new(
        id: GreeterId,
        inbox: mpsc::Receiver<GreetMessage>,
        outbox: mpsc::Sender<GreetResponse>,
    ) -> Self {
        Self {
            id,
            inbox,
            outbox,
            state: GreeterState { num_greeted: 0 },
        }
    }

    pub fn id(&self) -> GreeterId {
        self.id
    }

    pub fn process_message(&mut self) -> Result<()> {
        match self.inbox.try_recv() {
            Ok(m) => {
                let GreetMessage::Name(n) = m;
                self.outbox
                    .send(GreetResponse::Greeting(format!("Hello, {n}!")))
                    .map_err(convert_err)?;
                self.state.num_greeted += 1;
            }
            Err(e) => match e {
                TryRecvError::Empty => return Ok(()),
                TryRecvError::Disconnected => {
                    return Err("Outbox has been disconnected, actor in an improper state".into());
                }
            },
        }

        Ok(())
    }
}

use std::collections::HashMap;

struct Router {
    address_book: HashMap<GreeterId, mpsc::Sender<GreetMessage>>,
    next_id: GreeterId,
}

impl Router {
    pub fn new() -> Self {
        Self {
            address_book: HashMap::new(),
            next_id: 0,
        }
    }

    pub fn register(&mut self, sender: mpsc::Sender<GreetMessage>) -> GreeterId {
        let id = self.next_id;
        self.next_id += 1;
        self.address_book.insert(id, sender);
        id
    }

    pub fn unregister(&mut self, id: GreeterId) -> Option<mpsc::Sender<GreetMessage>> {
        self.address_book.remove(&id)
    }

    pub fn get_sender(&self, id: GreeterId) -> Option<&mpsc::Sender<GreetMessage>> {
        self.address_book.get(&id)
    }

    pub fn send(&self, id: GreeterId, message: GreetMessage) -> Result<()> {
        match self.address_book.get(&id) {
            Some(sender) => sender.send(message).map_err(convert_err),
            None => Err(format!("No sender found for id {}", id).into()),
        }
    }
}

struct Runtime {
    router: Router,
    greeters: Vec<Greeter>,
    response_rx: mpsc::Receiver<GreetResponse>,
    response_tx: mpsc::Sender<GreetResponse>,
}

impl Runtime {
    pub fn new() -> Self {
        let (response_tx, response_rx) = mpsc::channel();
        Self {
            router: Router::new(),
            greeters: Vec::new(),
            response_rx,
            response_tx,
        }
    }

    pub fn spawn_greeter(&mut self) -> GreeterId {
        let (inbox_tx, inbox_rx) = mpsc::channel();
        let id = self.router.register(inbox_tx);
        let greeter = Greeter::new(id, inbox_rx, self.response_tx.clone());
        self.greeters.push(greeter);
        id
    }

    pub fn send_message(&self, id: GreeterId, message: GreetMessage) -> Result<()> {
        self.router.send(id, message)
    }

    pub fn tick(&mut self) -> Result<()> {
        for greeter in &mut self.greeters {
            greeter.process_message()?;
        }
        Ok(())
    }

    pub fn try_recv_response(&self) -> Option<GreetResponse> {
        self.response_rx.try_recv().ok()
    }

    pub fn run_until_idle(&mut self) -> Result<()> {
        loop {
            self.tick()?;
            if self.response_rx.try_recv().is_err() {
                break;
            }
        }
        Ok(())
    }
}