faucet-drain

deadqueue::limited::Queue + tokio_util::sync::CancellationToken = faucet_drain::Faucet

Faucet is a back-pressured MPMC queue that can be drained after signaling completion.

Once completion is signaled, no more items can be added to the queue and only the remaining items in the queue can be drained. This property is useful for ensuring all items that were already queued are processed before shutting down.

You can freely clone() a Facuet to easily share it between asynchronous tasks for your producers and consumers. You don't need to wrap Faucet in an additional Arc since Faucet internally uses an Arc<deadqueue::limited::Queue<T>>

Example

You can clone this repo and run this example with cargo run --example sigint.

use std::error::Error;
use std::time::Duration;
use tokio::time::sleep;
use tokio::{spawn, try_join};
use tokio_util::sync::CancellationToken;
use faucet_drain::Faucet;

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    let app_cancellation = CancellationToken::new();
    ctrlc::set_handler({
        let cancellation = app_cancellation.clone();
        move || cancellation.cancel()
    })?;

    let faucet = Faucet::new_with_cancellation(5, app_cancellation.clone());

    let producer = spawn({
        let faucet = faucet.clone();
        async move {
            for i in 1.. {
                if faucet.push(i).await.is_break() { break; }
                sleep(Duration::from_millis(100)).await;
            }
        }
    });

    let consumer = spawn({
        let faucet = faucet.clone();
        async move {
            while let Some(i) = faucet.next().await {
                sleep(Duration::from_millis(500)).await;
                let status = if faucet.is_cancelled() { "drain" } else { "got" };
                println!("{status} #{i} ({} items waiting)", faucet.len());
            }
        }
    });

    try_join!(producer, consumer)?;
    println!("done");
    Ok(())
}

An example run:

got #1 (4 items waiting)
got #2 (5 items waiting)
^Cdrain #3 (5 items waiting)
drain #4 (4 items waiting)
drain #5 (3 items waiting)
drain #6 (2 items waiting)
drain #7 (1 items waiting)
drain #8 (0 items waiting)
done

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.