Comparing handles vs streams for async operations in rust

Question

In rust, we can write a vector of handles that allows to have asynchronous operation without blocking:

use tokio;

#[derive(Clone)]
struct Cont {
    delta: usize,
}

impl Cont {
    fn get(&mut self) -> usize {
        self.delta
    }
}

#[tokio::main]
async fn main() {
    let delta = 3;
    let cont = Cont { delta };
    let mut handles = Vec::new();
    for i in 0..10 {
        let mut cont = cont.clone();
        handles.push(tokio::spawn(async move {
            cont.get() + i.clone()
        }));
    }
    let _response = futures::future::join_all(handles).await;
}

But this builds a vector of handles which might be considered a negative.

The stream version would replace the main with

#[tokio::main]
async fn main() {
    let delta = 3;
    let cont = Cont { delta };
    let stream = stream::iter(0..10).then(|i| async move {
        cont.clone().get() + i.clone()
    });
    let _result : Vec<usize> = stream.collect().await;
}

Unfortunately, it does not compile.

So my questions are the following:

Is it possible to have the stream version of the code working correctly, that is, is there a way to clone the cont?
Apart from the building of a vector of handles, which does not occur in the stream version, are both versions the same? I mean, are they both based on green threads?

You haven't `use`d any `stream` so it's not clear what `stream::iter` is. Also, `use tokio;` is redundant. — cdhowie, May 13 '23 at 12:24

score 0 · Answer 1 · answered May 15 '23 at 15:59

Yup, it's doable:

fn main() {
    let delta = 3;
    let cont = Cont { delta };
    let stream = futures::stream::iter(0..10).then(move |i| {
        let mut cont = cont.clone();
        async move { cont.get() + i.clone() }
    });
    let _result: Vec<usize> = stream.collect().await;
}

Basically just clone the cont in the closure and then move it to the async block.

And yes, they are functionally equivalent.

Comparing handles vs streams for async operations in rust

1 Answers1