Merge pull request #80 from tnull/2024-01-async-event-queue

Implement `next_event_async` method polling the event queue

Author: tnull

Cargo.toml

@@ -25,3 +25,4 @@ serde_json = "1.0"
 
 [dev-dependencies]
 proptest = "1.0.0"
+tokio = { version = "1.35", default-features = false, features = [ "rt-multi-thread", "time", "sync", "macros" ] }

src/events.rs

@@ -20,24 +20,29 @@ use crate::lsps0;
 use crate::lsps1;
 use crate::lsps2;
 use crate::prelude::{Vec, VecDeque};
-use crate::sync::Mutex;
+use crate::sync::{Arc, Mutex};
+
+use core::future::Future;
+use core::task::{Poll, Waker};
 
 pub(crate) struct EventQueue {
-	queue: Mutex<VecDeque<Event>>,
+	queue: Arc<Mutex<VecDeque<Event>>>,
+	waker: Arc<Mutex<Option<Waker>>>,
 	#[cfg(feature = "std")]
 	condvar: std::sync::Condvar,
 }
 
 impl EventQueue {
 	pub fn new() -> Self {
-		let queue = Mutex::new(VecDeque::new());
+		let queue = Arc::new(Mutex::new(VecDeque::new()));
+		let waker = Arc::new(Mutex::new(None));
 		#[cfg(feature = "std")]
 		{
 			let condvar = std::sync::Condvar::new();
-			Self { queue, condvar }
+			Self { queue, waker, condvar }
 		}
 		#[cfg(not(feature = "std"))]
-		Self { queue }
+		Self { queue, waker }
 	}
 
 	pub fn enqueue(&self, event: Event) {
@@ -46,6 +51,9 @@ impl EventQueue {
 			queue.push_back(event);
 		}
 
+		if let Some(waker) = self.waker.lock().unwrap().take() {
+			waker.wake();
+		}
 		#[cfg(feature = "std")]
 		self.condvar.notify_one();
 	}
@@ -54,6 +62,10 @@ impl EventQueue {
 		self.queue.lock().unwrap().pop_front()
 	}
 
+	pub async fn next_event_async(&self) -> Event {
+		EventFuture { event_queue: Arc::clone(&self.queue), waker: Arc::clone(&self.waker) }.await
+	}
+
 	#[cfg(feature = "std")]
 	pub fn wait_next_event(&self) -> Event {
 		let mut queue =
@@ -65,6 +77,10 @@ impl EventQueue {
 		drop(queue);
 
 		if should_notify {
+			if let Some(waker) = self.waker.lock().unwrap().take() {
+				waker.wake();
+			}
+
 			self.condvar.notify_one();
 		}
 
@@ -92,3 +108,132 @@ pub enum Event {
 	/// An LSPS2 (JIT Channel) server event.
 	LSPS2Service(lsps2::event::LSPS2ServiceEvent),
 }
+
+struct EventFuture {
+	event_queue: Arc<Mutex<VecDeque<Event>>>,
+	waker: Arc<Mutex<Option<Waker>>>,
+}
+
+impl Future for EventFuture {
+	type Output = Event;
+
+	fn poll(
+		self: core::pin::Pin<&mut Self>, cx: &mut core::task::Context<'_>,
+	) -> core::task::Poll<Self::Output> {
+		if let Some(event) = self.event_queue.lock().unwrap().pop_front() {
+			Poll::Ready(event)
+		} else {
+			*self.waker.lock().unwrap() = Some(cx.waker().clone());
+			Poll::Pending
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use crate::lsps0::event::LSPS0ClientEvent;
+	use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
+
+	#[tokio::test]
+	#[cfg(feature = "std")]
+	async fn event_queue_works() {
+		use core::sync::atomic::{AtomicU16, Ordering};
+		use std::sync::Arc;
+		use std::time::Duration;
+
+		let event_queue = Arc::new(EventQueue::new());
+		assert_eq!(event_queue.next_event(), None);
+
+		let secp_ctx = Secp256k1::new();
+		let counterparty_node_id =
+			PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32]).unwrap());
+		let expected_event = Event::LSPS0Client(LSPS0ClientEvent::ListProtocolsResponse {
+			counterparty_node_id,
+			protocols: Vec::new(),
+		});
+
+		for _ in 0..3 {
+			event_queue.enqueue(expected_event.clone());
+		}
+
+		assert_eq!(event_queue.wait_next_event(), expected_event);
+		assert_eq!(event_queue.next_event_async().await, expected_event);
+		assert_eq!(event_queue.next_event(), Some(expected_event.clone()));
+		assert_eq!(event_queue.next_event(), None);
+
+		// Check `next_event_async` won't return if the queue is empty and always rather timeout.
+		tokio::select! {
+			_ = tokio::time::sleep(Duration::from_millis(10)) => {
+				// Timeout
+			}
+			_ = event_queue.next_event_async() => {
+				panic!();
+			}
+		}
+		assert_eq!(event_queue.next_event(), None);
+
+		// Check we get the expected number of events when polling/enqueuing concurrently.
+		let enqueued_events = AtomicU16::new(0);
+		let received_events = AtomicU16::new(0);
+		let mut delayed_enqueue = false;
+
+		for _ in 0..25 {
+			event_queue.enqueue(expected_event.clone());
+			enqueued_events.fetch_add(1, Ordering::SeqCst);
+		}
+
+		loop {
+			tokio::select! {
+				_ = tokio::time::sleep(Duration::from_millis(10)), if !delayed_enqueue => {
+					event_queue.enqueue(expected_event.clone());
+					enqueued_events.fetch_add(1, Ordering::SeqCst);
+					delayed_enqueue = true;
+				}
+				e = event_queue.next_event_async() => {
+					assert_eq!(e, expected_event);
+					received_events.fetch_add(1, Ordering::SeqCst);
+
+					event_queue.enqueue(expected_event.clone());
+					enqueued_events.fetch_add(1, Ordering::SeqCst);
+				}
+				e = event_queue.next_event_async() => {
+					assert_eq!(e, expected_event);
+					received_events.fetch_add(1, Ordering::SeqCst);
+				}
+			}
+
+			if delayed_enqueue
+				&& received_events.load(Ordering::SeqCst) == enqueued_events.load(Ordering::SeqCst)
+			{
+				break;
+			}
+		}
+		assert_eq!(event_queue.next_event(), None);
+
+		// Check we operate correctly, even when mixing and matching blocking and async API calls.
+		let (tx, mut rx) = tokio::sync::watch::channel(());
+		let thread_queue = Arc::clone(&event_queue);
+		let thread_event = expected_event.clone();
+		std::thread::spawn(move || {
+			let e = thread_queue.wait_next_event();
+			assert_eq!(e, thread_event);
+			tx.send(()).unwrap();
+		});
+
+		let thread_queue = Arc::clone(&event_queue);
+		let thread_event = expected_event.clone();
+		std::thread::spawn(move || {
+			// Sleep a bit before we enqueue the events everybody is waiting for.
+			std::thread::sleep(Duration::from_millis(20));
+			thread_queue.enqueue(thread_event.clone());
+			thread_queue.enqueue(thread_event.clone());
+		});
+
+		let e = event_queue.next_event_async().await;
+		assert_eq!(e, expected_event.clone());
+
+		rx.changed().await.unwrap();
+		assert_eq!(event_queue.next_event(), None);
+	}
+}

src/manager.rs

@@ -305,6 +305,13 @@ where {
 		self.pending_events.next_event()
 	}
 
+	/// Asynchronously polls the event queue and returns once the next event is ready.
+	///
+	/// Typically you would spawn a thread or task that calls this in a loop.
+	pub async fn next_event_async(&self) -> Event {
+		self.pending_events.next_event_async().await
+	}
+
 	/// Returns and clears all events without blocking.
 	///
 	/// Typically you would spawn a thread or task that calls this in a loop.