How to manually poll Runtime to drive futures without blocking current thread?

[alshdavid]

Hey all, I am trying to bolt tokio onto an external event loop (libuv via a Nodejs addon).

For this, I need to enter tokio and manually drive futures to completion using a current thread scheduler which does not block if there are pending futures.

Essentially, I need it to loop over all of the internal futures, poll them, continuing on pending futures.

Currently tokio only has the block_on method which blocks the main thread (consequently blocking the external event loop). I essentially need a try_next_tick() method.

I've been trying to reconstruct the CurrentThread scheduler in user code but almost all of the internals required to do this are private to the tokio crate - and I don't want to fork Tokio.

Is there an obvious way to achieve this that I am missing?

I was able to achieve this successfully with smol::LocalExecutor::try_tick() but I'd rather use Tokio.

Trying to get this working with Tokio in a sandbox I am trying the following:

fn main() {
  let runtime = Builder::new_current_thread().enable_all().build().unwrap();

  let mut handle = runtime.spawn(async {
    println!("1");
    tokio::time::sleep(Duration::from_secs(1)).await;
    println!("2");
  });

  let _ = runtime.enter();

  // external event loop
  loop { 
    poll::poll_fn(|ctx| {
      Future::poll(Pin::new(&mut handle), ctx)
    });
  }
}

I have tried using a LocalSet but I figure if I can run a single future like this, I can run a LocalSet like this so I am starting simple

EDIT: I am trying to achieve something similar to this

fn main() {
  let ex = smol::LocalExecutor::new();

  ex.spawn(async {
    println!("1");
    tokio::time::sleep(Duration::from_secs(1)).await;
    println!("2");
  }).detach();

  // external event loop
  loop { 
    ex.try_tick();
    if ex.is_empty() {
      break;
    }
  }
}

[RainM]

Hi. Do you have any updates here?

[mox692]

As far as I know, there is no such an api that does runtime task polling right now.

[tmm1]

Are you using napi-rs or rolling your own integration?

EDIT: Found napi-rs/napi-rs#2152 and https://github.com/alshdavid/napi_ext