refactor(event cache): move the listening to linked chunk updates to its own function, and introduce a select! at the top level

Author: bnjbvr

crates/matrix-sdk/src/event_cache/mod.rs

@@ -51,9 +51,12 @@ use matrix_sdk_base::{
 use matrix_sdk_common::executor::{spawn, JoinHandle};
 use room::RoomEventCacheState;
 use ruma::{events::AnySyncEphemeralRoomEvent, serde::Raw, OwnedEventId, OwnedRoomId, RoomId};
-use tokio::sync::{
-    broadcast::{channel, error::RecvError, Receiver, Sender},
-    mpsc, Mutex, RwLock,
+use tokio::{
+    select,
+    sync::{
+        broadcast::{channel, error::RecvError, Receiver, Sender},
+        mpsc, Mutex, RwLock,
+    },
 };
 use tracing::{debug, error, info, info_span, instrument, trace, warn, Instrument as _, Span};
 
@@ -417,6 +420,92 @@ impl EventCache {
         self.inner.room_event_cache_generic_update_sender.subscribe()
     }
 
+    async fn handle_thread_subscriber_linked_chunk_update(
+        client: &WeakClient,
+        thread_subscriber_sender: &Sender<()>,
+        up: RoomEventCacheLinkedChunkUpdate,
+    ) -> bool {
+        let Some(client) = client.get() else {
+            // Client shutting down.
+            debug!("Client is shutting down, exiting thread subscriber task");
+            return false;
+        };
+
+        let OwnedLinkedChunkId::Thread(room_id, thread_root) = &up.linked_chunk else {
+            trace!("received an update for a non-thread linked chunk, ignoring");
+            return true;
+        };
+
+        let Some(room) = client.get_room(&room_id) else {
+            warn!(%room_id, "unknown room");
+            return true;
+        };
+
+        let thread_root = thread_root.clone();
+
+        let new_events = up.events();
+        if new_events.is_empty() {
+            // No new events, nothing to do.
+            return true;
+        }
+
+        // This `PushContext` is going to be used to compute whether an in-thread event
+        // would trigger a mention.
+        //
+        // Of course, we're not interested in an in-thread event causing a mention,
+        // because it's part of a thread we've subscribed to. So the
+        // `PushContext` must not include the check for thread subscriptions (otherwise
+        // it would be impossible to subscribe to new threads).
+
+        let with_thread_subscriptions = false;
+
+        let Some(push_context) = room
+            .push_context_internal(with_thread_subscriptions)
+            .await
+            .inspect_err(|err| {
+                warn!("Failed to get push context for threads: {err}");
+            })
+            .ok()
+            .flatten()
+        else {
+            warn!("Missing push context for thread subscriptions.");
+            return true;
+        };
+
+        let mut subscribe_up_to = None;
+
+        // Find if there's an event that would trigger a mention for the current
+        // user, iterating from the end of the new events towards the oldest,
+        for ev in new_events.into_iter().rev() {
+            if push_context
+                .for_event(ev.raw())
+                .await
+                .into_iter()
+                .any(|action| action.should_notify())
+            {
+                let Some(event_id) = ev.event_id() else {
+                    // Shouldn't happen.
+                    continue;
+                };
+                subscribe_up_to = Some(event_id.to_owned());
+                break;
+            }
+        }
+
+        // And if we've found such a mention, subscribe to the thread up to this
+        // event.
+        if let Some(event_id) = subscribe_up_to {
+            trace!(thread = %thread_root, up_to = %event_id, "found a new thread to subscribe to");
+            if let Err(err) = room.subscribe_thread_if_needed(&thread_root, Some(event_id)).await {
+                warn!(%err, "Failed to subscribe to thread");
+            } else {
+                let _ = thread_subscriber_sender.send(());
+            }
+        }
+
+        return true;
+    }
+
     #[instrument(skip_all)]
     async fn thread_subscriber_task(
         client: WeakClient,
@@ -431,97 +520,23 @@ impl EventCache {
         let mut rx = linked_chunk_update_sender.subscribe();
 
         loop {
-            match rx.recv().await {
-                Ok(up) => {
-                    let Some(client) = client.get() else {
-                        // Client shutting down.
-                        debug!("Client is shutting down, exiting thread subscriber task");
-                        break;
-                    };
-
-                    let OwnedLinkedChunkId::Thread(room_id, thread_root) = &up.linked_chunk else {
-                        trace!("received an update for a non-thread linked chunk, ignoring");
-                        continue;
-                    };
-
-                    let Some(room) = client.get_room(&room_id) else {
-                        warn!(%room_id, "unknown room");
-                        continue;
-                    };
-
-                    let thread_root = thread_root.clone();
-
-                    let new_events = up.events();
-                    if new_events.is_empty() {
-                        // No new events, nothing to do.
-                        continue;
-                    }
-
-                    // This `PushContext` is going to be used to compute whether an in-thread event
-                    // would trigger a mention.
-                    //
-                    // Of course, we're not interested in an in-thread event causing a mention,
-                    // because it's part of a thread we've subscribed to. So the
-                    // `PushContext` must not include the check for thread subscriptions (otherwise
-                    // it would be impossible to subscribe to new threads).
-
-                    let with_thread_subscriptions = false;
-
-                    let Some(push_context) = room
-                        .push_context_internal(with_thread_subscriptions)
-                        .await
-                        .inspect_err(|err| {
-                            warn!("Failed to get push context for threads: {err}");
-                        })
-                        .ok()
-                        .flatten()
-                    else {
-                        warn!("Missing push context for thread subscriptions.");
-                        continue;
-                    };
-
-                    let mut subscribe_up_to = None;
-
-                    // Find if there's an event that would trigger a mention for the current
-                    // user, iterating from the end of the new events towards the oldest,
-                    for ev in new_events.into_iter().rev() {
-                        if push_context
-                            .for_event(ev.raw())
-                            .await
-                            .into_iter()
-                            .any(|action| action.should_notify())
-                        {
-                            let Some(event_id) = ev.event_id() else {
-                                // Shouldn't happen.
-                                continue;
-                            };
-                            subscribe_up_to = Some(event_id.to_owned());
+            select! {
+                res = rx.recv() => {
+                    match res {
+                        Ok(up) => {
+                            if !Self::handle_thread_subscriber_linked_chunk_update(&client, &thread_subscriber_sender, up).await {
+                                break;
+                            }
+                        }
+                        Err(RecvError::Closed) => {
+                            debug!("Linked chunk update channel has been closed, exiting thread subscriber task");
                             break;
                         }
-                    }
-
-                    // And if we've found such a mention, subscribe to the thread up to this
-                    // event.
-                    if let Some(event_id) = subscribe_up_to {
-                        trace!(thread = %thread_root, up_to = %event_id, "found a new thread to subscribe to");
-                        if let Err(err) =
-                            room.subscribe_thread_if_needed(&thread_root, Some(event_id)).await
-                        {
-                            warn!(%err, "Failed to subscribe to thread");
-                        } else {
-                            let _ = thread_subscriber_sender.send(());
+                        Err(RecvError::Lagged(num_skipped)) => {
+                            warn!(num_skipped, "Lagged behind linked chunk updates");
                         }
                     }
                 }
-
-                Err(RecvError::Closed) => {
-                    debug!("Linked chunk update channel has been closed, exiting thread subscriber task");
-                    break;
-                }
-
-                Err(RecvError::Lagged(num_skipped)) => {
-                    warn!(num_skipped, "Lagged behind linked chunk updates");
-                }
             }
         }
     }