Tokio: number of concurrent tasks

2

The FuturesUnordered type is very useful for this, because it allows you to wait until one task has finished, and then lets you do some more work.

use futures::stream::StreamExt; // for next()

let mut futs = FuturesUnordered::new();
let mut outputs = Vec::new();

for i in 0..100 {
    let fut = async move { };
    futs.push(fut); // tokio::spawn is optional here

    if futs.len() == 10 {
        // this wont return None because futs is not empty
        outputs.push(futs.next().await.unwrap());
    }
}
// wait for remaining
while let Some(item) = futs.next().await {
    outputs.push(item);
}
5 Likes