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//! This crate provides a lock-free Pub/Sub event-bus based on the Disruptor pattern from LMAX. //! //! Both sync and async APIs are available. //! //! # Why? //! //! Event-buses ease the development burden of concurrent programs by enabling concurrent //! application subroutines to interact and affect other subroutines through events. Of course, //! a poor implementation can become a serious bottleneck depending on the application's needs. //! //! Eventador supports the Rust model of *Choose Your Guarantees ™* by presenting //! configuration options for how to handle event publishing when consumers are lagging. //! Providing this configurable interface is currently a work in progress. //! //! # Examples //! //! Please use the provided [examples](#) for a more thorough approach on how to use this crate. //! //! # Design Considerations //! //! ## Ring Buffer //! //! Like Eventador, most event-bus implementations use some form of ring buffer for the underlying //! data structure to store published events. As such, an Eventador instance cannot indefinitely //! grow to accommodate events, unlike a [`Vec`]. In the strictest model (and Eventador's default //! approach), new events must overwrite the oldest event that has already been read by all its //! subscribers. In other words, publishers cannot publish an event to the ring buffer until all //! subscribers for the next overwrite-able event have consumed it. This model favors the //! subscribers so that no event is lost or overwritten without first being handled by every //! concerned party. //! //! Other implementations, like [bus-queue](https://github.com/filipdulic/bus-queue), solve this //! problem by ignoring lagging subscribers, and treating publishers as first-class operators. This //! is the opposite extreme to Eventador's default. //! //! Ultimately, there should not have to be a compromise between what a user wants to prioritize. //! How an event-bus handles the lagging-consumer problem should be left to the user to decide //! through configuration. //! //! ## LMAX Disruptor //! //! The LMAX Disruptor serves as a basis for a lot of event-bus implementations, though the //! contemporary architecture of the Disruptor looks very different from the one presented in the //! outdated LMAX white-paper. Eventador draws from the principles of the current Disruptor //! architecture, but the similarities stop there. //! //! A sequencer atomically assigns an event to an index in the ring buffer on publishing of an //! event. //! //! Subscribers internally have their own sequencer to determine their last read event in the ring //! buffer. On receiving a subscribed message, the sequencer is atomically updated to reflect that //! it can now receive the next event. //! //! ## Lock-free //! //! Eventador has the potential to be a high-contention (aka bottlenecking) structure to a given //! concurrent program, so the implementation needs to handle contention as effectively as possible. //! Atomic CAS operations are generally faster than locking, and is the preferred approach to handle //! contention. //! //! ## TypeId //! This crate relies on the use of `TypeId` to determine what type an event is, and what types of //! events a subscriber subscribes to. //! mod event; mod futures; mod ring_buffer; mod sequence; mod subscriber; pub use crate::futures::{AsyncPublisher, AsyncSubscriber}; pub use ::futures::{SinkExt, StreamExt}; pub use event::EventRead; pub use subscriber::Subscriber; use crate::ring_buffer::RingBuffer; use crate::sequence::Sequence; use std::sync::Arc; /// A lock-free and thread-safe event-bus implementation /// /// # Example /// /// Basic usage: /// /// ```ignore /// let eventbus = Eventador::new(4)?; /// let subscriber = eventbus.subscribe::<usize>(); /// /// let mut i: usize = 1234; /// eventbus.publish(i); /// /// let mut msg = subscriber.recv().unwrap(); /// assert_eq!(i, *msg); /// ``` /// #[derive(Clone)] pub struct Eventador { ring: Arc<RingBuffer>, } impl Eventador { /// Creates a new Eventador event-bus /// /// **The capacity is required to be a power of 2.** /// /// # Example /// /// Basic usage: /// /// ```ignore /// let eventbus = Eventador::new(4)?; /// ``` /// pub fn new(capacity: u64) -> anyhow::Result<Self> { Ok(Self { ring: Arc::new(RingBuffer::new(capacity)?), }) } /// Publishes an event on the event-bus /// /// # Example /// /// Basic usage: /// /// ```ignore /// let eventbus = Eventador::new(4)?; /// /// let mut i: usize = 1234; /// eventbus.publish(i); /// ``` /// pub fn publish<T: 'static + Send>(&self, message: T) { let sequence = self.ring.next(); if let Some(event_store) = self.ring.get_envelope(sequence).clone() { event_store.overwrite::<T>(sequence, message); } } /// Creates a [`Subscriber`] that is subscribed to events of the provided type /// /// The [`Subscriber`] will not receive intended events that were published to the event-bus /// before time of subscription. It will only receive intended events that are published after /// time of subscription. /// /// # Example /// /// Basic usage: /// /// ```ignore /// let eventbus = Eventador::new(4)?; /// /// // subscribe first, before publishing! /// let subscriber = eventbus.subscribe::<usize>(); /// /// let mut i: usize = 1234; /// eventbus.publish(i); /// /// let mut msg = subscriber.recv().unwrap(); /// assert_eq!(i, *msg); /// ``` /// pub fn subscribe<T: 'static + Send>(&self) -> Subscriber<T> { let sequence = Arc::new(Sequence::with_value(self.ring.sequencer().get() + 1)); self.ring .sequencer() .register_gating_sequence(sequence.clone()); Subscriber::new(self.ring.as_ref(), sequence) } /// Creates an [`AsyncPublisher`] that can publish to the event-bus asynchronously /// /// # Example /// /// Basic usage: /// /// ```ignore /// let eventbus = Eventador::new(4)?; /// let mut publisher: AsyncPublisher<usize> = eventbus.async_publisher(); /// /// let mut i: usize = 1234; /// publisher.send(i).await?; /// ``` /// pub fn async_publisher<T: 'static + Send + Unpin>(&self) -> AsyncPublisher<T> { AsyncPublisher::new(self.ring.clone()) } /// Creates an [`AsyncSubscriber`] that can subscribe to events and receive them asynchronously /// /// # Example /// /// Basic usage: /// /// ```ignore /// let eventbus = Eventador::new(4)?; /// /// let subscriber = disruptor.async_subscriber::<usize>(); /// let mut publisher: AsyncPublisher<usize> = disruptor.async_publisher(); /// /// let mut i: usize = 1234; /// publisher.send(i).await?; /// /// let mut msg = subscriber.recv().await.unwrap(); /// assert_eq!(i, *msg); /// ``` /// pub fn async_subscriber<T: 'static + Send + Unpin>(&self) -> AsyncSubscriber<T> { let sequence = Arc::new(Sequence::with_value(self.ring.sequencer().get() + 1)); self.ring .sequencer() .register_gating_sequence(sequence.clone()); AsyncSubscriber::new(self.ring.clone(), sequence) } } impl From<RingBuffer> for Eventador { fn from(ring: RingBuffer) -> Self { Self { ring: Arc::new(ring), } } } impl From<Arc<RingBuffer>> for Eventador { fn from(ring: Arc<RingBuffer>) -> Self { Self { ring } } } #[cfg(test)] mod tests { use crate::futures::publisher::AsyncPublisher; use crate::Eventador; use async_channel::{unbounded, RecvError}; use futures::SinkExt; use ntest::timeout; #[test] fn publish_and_subscribe() { let res = Eventador::new(4); assert!(res.is_ok()); let disruptor: Eventador = res.unwrap(); let subscriber = disruptor.subscribe::<usize>(); assert_eq!(1, subscriber.sequence()); // @todo double check if it should be this way let mut i: usize = 1234; disruptor.publish(i); let mut msg = subscriber.recv().unwrap(); assert_eq!(i, *msg); i += 1111; let disruptor2 = disruptor.clone(); std::thread::spawn(move || { std::thread::sleep(std::time::Duration::from_secs(1)); disruptor2.publish(i); }); msg = subscriber.recv().unwrap(); assert_eq!(i, *msg); } #[async_std::test] #[timeout(5000)] async fn async_publish() { let res = Eventador::new(4); assert!(res.is_ok()); let disruptor: Eventador = res.unwrap(); let subscriber = disruptor.async_subscriber::<usize>(); let mut publisher: AsyncPublisher<usize> = disruptor.async_publisher(); let (sender, mut receiver) = unbounded::<Result<usize, RecvError>>(); let mut i: usize = 1234; let mut sent = sender.send(Ok(i)).await; assert!(sent.is_ok()); let handle = async_std::task::spawn(async move { publisher.send_all(&mut receiver).await.unwrap(); }); let mut msg = subscriber.recv().await.unwrap(); assert_eq!(i, *msg); println!("Passed part 1!"); i += 1111; let disruptor2 = disruptor.clone(); async_std::task::spawn(async move { async_std::task::sleep(std::time::Duration::from_secs(1)).await; disruptor2.publish(i); }); msg = subscriber.recv().await.unwrap(); assert_eq!(i, *msg); println!("Passed part 2!"); i += 1111; sent = sender.send(Ok(i)).await; assert!(sent.is_ok()); msg = subscriber.recv().await.unwrap(); assert_eq!(i, *msg); println!("Passed part 3! Done."); assert!(handle.cancel().await.is_none()); } #[derive(Debug, Eq, PartialEq)] enum TestEnum { SampleA, } #[test] fn enum_specific_subscription() { let res = Eventador::new(4); assert!(res.is_ok()); println!("Passed part 1!"); let disruptor: Eventador = res.unwrap(); let subscriber = disruptor.subscribe::<TestEnum>(); assert_eq!(1, subscriber.sequence()); // @todo double check if it should be this way println!("Passed part 2!"); disruptor.publish(TestEnum::SampleA); let msg = subscriber.recv().unwrap(); assert_eq!(TestEnum::SampleA, *msg); println!("Passed part 3! Done."); } }