From 402c9a046741562650a2ed421b777ff3cace02f2 Mon Sep 17 00:00:00 2001
From: chocy <please@leash.me>
Date: Sat, 21 Mar 2026 18:30:30 +0100
Subject: [PATCH] fix(sync): stop prior long-poll on reconnection

---
 src/api/client/sync/v5.rs | 11 +++++-----
 src/service/sync/mod.rs   | 42 ++++++++++++++++++++++++++-------------
 2 files changed, 33 insertions(+), 20 deletions(-)

diff --git a/src/api/client/sync/v5.rs b/src/api/client/sync/v5.rs
index e1d46d26d..634c11c6b 100644
--- a/src/api/client/sync/v5.rs
+++ b/src/api/client/sync/v5.rs
@@ -101,7 +101,7 @@ pub(crate) async fn sync_events_v5_route(
 		.unwrap_or(0);
 
 	let conn_key = into_connection_key(sender_user, sender_device, request.conn_id.as_deref());
-	let conn_val = services
+	let (conn_val, superseded) = services
 		.sync
 		.load_or_init_connection(&conn_key)
 		.await;
@@ -196,11 +196,10 @@ pub(crate) async fn sync_events_v5_route(
 
 		if timeout == 0
 			|| services.server.is_stopping()
-			|| timeout_at(stop_at, watchers)
-				.boxed()
-				.await
-				.is_err()
-		{
+			|| tokio::select! {
+				() = superseded.notified() => true,
+				result = timeout_at(stop_at, watchers).boxed() => result.is_err(),
+			} {
 			response.pos = conn.next_batch.to_string().into();
 			trace!(conn.globalsince, conn.next_batch, "timeout; empty response {response:?}");
 			conn.store(&services.sync, &conn_key);
diff --git a/src/service/sync/mod.rs b/src/service/sync/mod.rs
index 13264a6b1..33c6fa9c9 100644
--- a/src/service/sync/mod.rs
+++ b/src/service/sync/mod.rs
@@ -14,7 +14,7 @@ use ruma::{
 	},
 };
 use serde::{Deserialize, Serialize};
-use tokio::sync::Mutex as TokioMutex;
+use tokio::sync::{Mutex as TokioMutex, Notify};
 use tuwunel_core::{Result, at, debug, err, implement, is_equal_to, utils::stream::TryIgnore};
 use tuwunel_database::{Cbor, Deserialized, Map};
 
@@ -57,9 +57,10 @@ pub struct Room {
 	pub roomsince: u64,
 }
 
-type Connections = TokioMutex<BTreeMap<ConnectionKey, ConnectionVal>>;
 pub type ConnectionVal = Arc<TokioMutex<Connection>>;
+pub type ConnectionEntry = (ConnectionVal, Arc<Notify>);
 pub type ConnectionKey = (OwnedUserId, Option<OwnedDeviceId>, Option<ConnectionId>);
+type Connections = TokioMutex<BTreeMap<ConnectionKey, ConnectionEntry>>;
 
 pub type Subscriptions = BTreeMap<OwnedRoomId, request::ListConfig>;
 pub type Lists = BTreeMap<ListId, request::List>;
@@ -102,22 +103,22 @@ pub async fn clear_connections(
 	device_id: Option<&DeviceId>,
 	conn_id: Option<&ConnectionId>,
 ) {
-	self.connections
-		.lock()
-		.await
-		.retain(|(conn_user_id, conn_device_id, conn_conn_id), _| {
+	self.connections.lock().await.retain(
+		|(conn_user_id, conn_device_id, conn_conn_id), (_, notify)| {
 			let retain = user_id.is_none_or(is_equal_to!(conn_user_id))
 				&& (device_id.is_none() || device_id == conn_device_id.as_deref())
 				&& (conn_id.is_none() || conn_id == conn_conn_id.as_ref());
 
 			if !retain {
+				notify.notify_waiters();
 				self.db
 					.userdeviceconnid_conn
 					.del((conn_user_id, conn_device_id, conn_conn_id));
 			}
 
 			retain
-		});
+		},
+	);
 }
 
 #[implement(Service)]
@@ -126,16 +127,24 @@ pub async fn drop_connection(&self, key: &ConnectionKey) {
 	let mut cache = self.connections.lock().await;
 
 	self.db.userdeviceconnid_conn.del(key);
-	cache.remove(key);
+	if let Some((_, notify)) = cache.remove(key) {
+		notify.notify_waiters();
+	}
 }
 
 #[implement(Service)]
 #[tracing::instrument(level = "debug", skip(self))]
-pub async fn load_or_init_connection(&self, key: &ConnectionKey) -> ConnectionVal {
+pub async fn load_or_init_connection(&self, key: &ConnectionKey) -> ConnectionEntry {
 	let mut cache = self.connections.lock().await;
 
 	match cache.entry(key.clone()) {
-		| Entry::Occupied(val) => val.get().clone(),
+		| Entry::Occupied(mut entry) => {
+			entry.get().1.notify_waiters();
+			let conn = entry.get().0.clone();
+			let notify = Arc::new(Notify::new());
+			entry.insert((conn.clone(), notify.clone()));
+			(conn, notify)
+		},
 		| Entry::Vacant(val) => {
 			let conn = self
 				.db
@@ -149,7 +158,9 @@ pub async fn load_or_init_connection(&self, key: &ConnectionKey) -> ConnectionVa
 				.map(Arc::new)
 				.unwrap_or_default();
 
-			val.insert(conn).clone()
+			let notify = Arc::new(Notify::new());
+			let (conn, _) = val.insert((conn, notify.clone()));
+			(conn.clone(), notify)
 		},
 	}
 }
@@ -160,7 +171,7 @@ pub async fn load_connection(&self, key: &ConnectionKey) -> Result<ConnectionVal
 	let mut cache = self.connections.lock().await;
 
 	match cache.entry(key.clone()) {
-		| Entry::Occupied(val) => Ok(val.get().clone()),
+		| Entry::Occupied(val) => Ok(val.get().0.clone()),
 		| Entry::Vacant(val) => self
 			.db
 			.userdeviceconnid_conn
@@ -170,7 +181,10 @@ pub async fn load_connection(&self, key: &ConnectionKey) -> Result<ConnectionVal
 			.map(at!(0))
 			.map(TokioMutex::new)
 			.map(Arc::new)
-			.map(|conn| val.insert(conn).clone()),
+			.map(|conn| {
+				let notify = Arc::new(Notify::new());
+				val.insert((conn, notify)).0.clone()
+			}),
 	}
 }
 
@@ -181,7 +195,7 @@ pub async fn get_loaded_connection(&self, key: &ConnectionKey) -> Result<Connect
 		.lock()
 		.await
 		.get(key)
-		.cloned()
+		.map(|(conn, _)| conn.clone())
 		.ok_or_else(|| err!(Request(NotFound("Connection not found."))))
 }