Deadqueue

Deadqueue is a dead simple async queue with back pressure support.

This crate provides three implementations:

• Unlimited (deadqueue::unlimited::Queue)

  • Based on crossbeam_queue::SegQueue
  • Has unlimitied capacity and no back pressure on push
  • Enabled via the unlimited feature in your Cargo.toml

• Resizable (deadqueue::resizable::Queue)

  • Based on deadqueue::unlimited::Queue
  • Has limited capacity with back pressure on push
  • Supports resizing
  • Enabled via the resizable feature in your Cargo.toml

• Limited (deadqueue::limited::Queue)

  • Based on crossbeam_queue::ArrayQueue
  • Has limit capacity with back pressure on push
  • Does not support resizing
  • Enabled via the limited feature in your Cargo.toml

Features

Feature	Description	Extra dependencies	Default
unlimited	Enable unlimited queue implementation	–	yes
resizable	Enable resizable queue implementation	deadqueue/unlimited	yes
limited	Enable limited queue implementation	–	yes

Example

use std::sync::Arc;
use tokio::time::{sleep, Duration};

const TASK_COUNT: usize = 1000;
const WORKER_COUNT: usize = 10;

type TaskQueue = deadqueue::limited::Queue<usize>;

#[tokio::main]
async fn main() {
    let queue = Arc::new(TaskQueue::new(TASK_COUNT));
    for i in 0..TASK_COUNT {
        queue.try_push(i).unwrap();
    }
    for worker in 0..WORKER_COUNT {
        let queue = queue.clone();
        tokio::spawn(async move {
            loop {
                let task = queue.pop().await;
                println!("worker[{}] processing task[{}] ...", worker, task);
            }
        });
    }
    println!("Waiting for workers to finish...");
    queue.wait_empty().await;
    println!("All tasks done. :-)");
}

Reasons for yet another queue

Deadqueue is by no means the only queue implementation available. It does things a little different and provides features that other implementations are lacking:

• Resizable queue. Usually you have to pick between limited and unlimited queues. This crate features a resizable Queue which can be resized as needed. This is probably a big unique selling point of this crate.

• Introspection support. The methods .len(), .capacity() and .available() provide access the current state of the queue.

• Fair scheduling. Tasks calling pop will receive items in a first-come-first-serve fashion. This is mainly due to the use of tokio::sync::Semaphore which is fair by nature.

• One struct, not two. The channels of tokio, async_std and futures-intrusive split the queue in two structs (Sender and Receiver) which makes the usage sligthly more complicated.

• Bring your own Arc. Since there is no separation between Sender and Receiver there is also no need for an internal Arc. (All implementations that split the channel into a Sender and Receiver need some kind of Arc internally.)

• Fully concurrent access. No need to wrap the Receiver part in a Mutex. All methods support concurrent accesswithout the need for an additional synchronization primitive.

• Support for try__ methods. The methods try_push and try_pop can be used to access the queue from non-blocking synchroneous code.

• Support for detecting when the queue becomes empty or full, using the wait_empty, subscribe_empty, wait_full and subscribe_full methods.

Alternatives

Crate	Limitations	Documentation
tokio	No resizable queue. No introspection support. Synchronization of Receiver needed.	tokio::sync::mpsc::channel, tokio::sync::mpsc::unbounded_channel
async-std	No resizable or unlimited queue. No introspection support. No try_send or try_recv methods.	async_std::sync::channel
futures	No resizable queue. No introspection support.	futures::channel::mpsc::channel, futures::channel::mpsc::unbounded

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.