[net-tokio] Call PeerManager::process_events without blocking reads

Unlike very ancient versions of lightning-net-tokio, this does not
rely on a single global process_events future, but instead has one
per connection. This could still cause significant contention, so
we'll ensure only two process_events calls can exist at once in
the next few commits.

Author: TheBlueMatt

lightning-net-tokio/src/lib.rs

@@ -118,11 +118,28 @@ struct Connection {
 	id: u64,
 }
 impl Connection {
+	async fn poll_event_process<CMH, RMH, L, UMH>(peer_manager: Arc<peer_handler::PeerManager<SocketDescriptor, Arc<CMH>, Arc<RMH>, Arc<L>, Arc<UMH>>>, mut event_receiver: mpsc::Receiver<()>) where
+			CMH: ChannelMessageHandler + 'static + Send + Sync,
+			RMH: RoutingMessageHandler + 'static + Send + Sync,
+			L: Logger + 'static + ?Sized + Send + Sync,
+			UMH: CustomMessageHandler + 'static + Send + Sync {
+		loop {
+			if event_receiver.recv().await.is_none() {
+				return;
+			}
+			peer_manager.process_events();
+		}
+	}
+
 	async fn schedule_read<CMH, RMH, L, UMH>(peer_manager: Arc<peer_handler::PeerManager<SocketDescriptor, Arc<CMH>, Arc<RMH>, Arc<L>, Arc<UMH>>>, us: Arc<Mutex<Self>>, mut reader: io::ReadHalf<TcpStream>, mut read_wake_receiver: mpsc::Receiver<()>, mut write_avail_receiver: mpsc::Receiver<()>) where
-			CMH: ChannelMessageHandler + 'static,
-			RMH: RoutingMessageHandler + 'static,
-			L: Logger + 'static + ?Sized,
-			UMH: CustomMessageHandler + 'static {
+			CMH: ChannelMessageHandler + 'static + Send + Sync,
+			RMH: RoutingMessageHandler + 'static + Send + Sync,
+			L: Logger + 'static + ?Sized + Send + Sync,
+			UMH: CustomMessageHandler + 'static + Send + Sync {
+		// Create a waker to wake up poll_event_process, above
+		let (event_waker, event_receiver) = mpsc::channel(1);
+		tokio::spawn(Self::poll_event_process(Arc::clone(&peer_manager), event_receiver));
+
 		// 8KB is nice and big but also should never cause any issues with stack overflowing.
 		let mut buf = [0; 8192];
 
@@ -173,7 +190,7 @@ impl Connection {
 					Err(_) => break Disconnect::PeerDisconnected,
 				},
 			}
-			peer_manager.process_events();
+			let _ = event_waker.try_send(());
 		};
 		let writer_option = us.lock().unwrap().writer.take();
 		if let Some(mut writer) = writer_option {