How to cancel an infinite stream from within the stream itself?

For cases where you want to cancel a stream from outside of the stream, see stream-cancel.

---

For your specific case, it's easiest to convert your collection into a stream and zip it together with the interval timer. This way, the resulting stream naturally stops when the collection is empty:

use futures::{future, stream, Stream}; // 0.1.29
use std::time::Duration;
use tokio; // 0.1.22
use tokio_timer::Interval; // 0.2.11

fn main() {
    tokio::run({
        let some_vars = vec![1, 2, 3, 4, 5, 6, 7, 8];

        let timer =
            Interval::new_interval(Duration::from_millis(100)).map_err(|e| panic!("Error: {}", e));

        let some_vars = stream::iter_ok(some_vars.into_iter().rev());
        let combined = timer.zip(some_vars);

        combined.for_each(move |(_, item)| {
            eprintln!("Woke up");

            tokio::spawn(future::lazy(move || {
                println!("{:?}", item);
                Ok(())
            }));

            Ok(())
        })
    });
}

Otherwise, you can stop the stream by using and_then to both remove the value from the collection and control if the stream should continue:

use futures::{future, Stream}; // 0.1.29
use std::time::Duration;
use tokio; // 0.1.22
use tokio_timer::Interval; // 0.2.11

fn main() {
    tokio::run({
        let mut some_vars = vec![1, 2, 3, 4, 5, 6, 7, 8];

        let timer =
            Interval::new_interval(Duration::from_millis(100)).map_err(|e| panic!("Error: {}", e));

        let limited = timer.and_then(move |_| {
            if some_vars.len() <= 4 {
                Err(())
            } else {
                some_vars.pop().ok_or(())
            }
        });

        limited.for_each(move |item| {
            eprintln!("Woke up");

            tokio::spawn(future::lazy(move || {
                println!("{:?}", item);
                Ok(())
            }));

            Ok(())
        })
    });
}