Asynchronous Deferred Calls

This crate implements the Active Object design pattern.

The entry point of this crate is Dispatcher, which wraps an Arc<Lock<T>>.

Note: Lock can be RwLock or Mutex from the async-lock crate.

Dispatcher

The Dispatcher allows you to create Callers for some methods on T.

You can then schedule deferred calls to these methods via these Callers.

Dispatcher implements Future; You must await this future for calls to actually be dispatched.

Caller

When you create a Caller for a method of T using Dispatcher, a background task is created, waiting for you to schedule deferred calls via the Caller. When a call is scheduled, the background task will lock the RwLock or Mutex and call the method on the locked T instance.

Compatible T methods

The methods must:

• be asynchronous
• return an implementer of ReturnType

They can take self mutably or immutably.

Note: you can use a freestanding function instead of a method if the first parameter of that function is &T or &mut T.

Summoner

if the method's last parameter is an async_channel::Sender, you can turn your Caller into a Summoner, which makes it easy to wait for a reply when you schedule a call.

Example

use async_defer::{*, async_channel::Sender, async_lock::RwLock};
use std::time::{Instant, Duration};
use std::sync::Arc;

// An example object which will be modified in deferred calls
struct Subject;

impl Subject {
    async fn print(&mut self, msg: String) -> Result<(), String> {
        println!("msg: {}", msg);
        Ok(())
    }

    async fn ping_pong(&self, payload: u8, reply: Sender<u8>) -> Result<(), String> {
        let _ = reply.send(payload).await;
        Ok(())
    }
}

let world = Arc::new(RwLock::new(Subject));
let mut dispatcher = Dispatcher::new(world);

let deferred_print = dispatcher.listen_mut_1(Subject::print);
let deferred_ping_pong = dispatcher.listen_ref_2(Subject::ping_pong);

async {
    deferred_print.call("Hello World".to_string()).await;

    let later = Instant::now() + Duration::from_secs(5);
    deferred_print.call_later(later, "Hello World".to_string()).await;

    // `ping_pong` has a reply parameter,
    // allowing us to create a `Summoner`.
    let summoner = deferred_ping_pong.summoner();
    let rep = summoner.summon(5).await;
    println!("reply: {}", rep);
};

In this example, two background tasks are created, one for each method of Subject. The ping_pong method's last parameter is a Sender, allowing us to "summon" the method.