Could futures::executor::block_on() lead to deadlock when being invoked in a Monoio task?

[SteveLauC]

Hi, I would like to know if a use of futures::executor::block_on() within a Monoio task could potentially lead to a deadlock? If so, would you like to explain the causes?

BTW, Tokio's answer is yes

[ethe]

The same is true in monoio. Running the io-bound future in futures::block_on will cause the monoio reactor to lose the opportunity to react the io event, and futures::block_on will never be ready.

[SteveLauC]

This only happens if the task executed by futures::executor::block_on() depends on a task that is executed in your Monoio runtime though.

[ethe]

That's another case, io-bound or awaiting another monoio task will lead to deadlock.

[SteveLauC]

Oops, sorry that I didn't notice it, do you mean something like:

#[monoio::main]
async fn main() {
    let file = monoio::fs::File::open("Cargo.toml").await.unwrap();
    futures::executor::block_on(async move {
        let (result, buf) = file.read_at(vec![0_u8; 10], 0).await;
        println!("result {:?}, buf {:?}", result, buf);
    });
}

The above code snippet indeed blocks in my test. 🤔