From d710dafc94b413112553d16a19999345abad84ed Mon Sep 17 00:00:00 2001
From: Stefan Ceriu <stefanc@matrix.org>
Date: Tue, 16 May 2023 13:53:27 +0300
Subject: [PATCH] Adopt async uniffi in the RoomSummaryProvider and ensure
 diffs are still processed serially

---
 .../RoomSummary/RoomSummaryProvider.swift     | 27 +++++++++++++------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift b/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift
index 49286e454..7c8f9f803 100644
--- a/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift
+++ b/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift
@@ -109,6 +109,19 @@ class RoomSummaryProvider: RoomSummaryProviderProtocol {
         
         MXLog.info("\(name): Finished applying \(diffs.count) diffs, new room list \(rooms.compactMap { $0.id ?? "Empty" })")
     }
+    
+    // The room summary provider needs to process diffs serially
+    // Switching to an actor here doesn't help because of all the suspension points
+    // and actor re-entrance
+    private static var latestRoomMessage: EventTimelineItem?
+    private func fetchLastMessage(room: SlidingSyncRoomProtocol) {
+        let semaphore = DispatchSemaphore(value: 0)
+        Task {
+            Self.latestRoomMessage = await room.latestRoomMessage()
+            semaphore.signal()
+        }
+        semaphore.wait()
+    }
         
     private func buildRoomSummaryForIdentifier(_ identifier: String, invalidated: Bool) -> RoomSummary {
         guard let room = try? slidingSyncListProxy.roomForIdentifier(identifier) else {
@@ -119,14 +132,12 @@ class RoomSummaryProvider: RoomSummaryProviderProtocol {
         var attributedLastMessage: AttributedString?
         var lastMessageFormattedTimestamp: String?
         
-        // Dispatch onto another queue otherwise the rust method latestRoomMessage crashes.
-        // This will be fixed when we get async uniffi support.
-        DispatchQueue.global(qos: .userInitiated).sync {
-            if let latestRoomMessage = room.latestRoomMessage() {
-                let lastMessage = EventTimelineItemProxy(item: latestRoomMessage)
-                lastMessageFormattedTimestamp = lastMessage.timestamp.formattedMinimal()
-                attributedLastMessage = eventStringBuilder.buildAttributedString(for: lastMessage)
-            }
+        fetchLastMessage(room: room)
+        
+        if let latestRoomMessage = Self.latestRoomMessage {
+            let lastMessage = EventTimelineItemProxy(item: latestRoomMessage)
+            lastMessageFormattedTimestamp = lastMessage.timestamp.formattedMinimal()
+            attributedLastMessage = eventStringBuilder.buildAttributedString(for: lastMessage)
         }
         
         let fullRoom = room.fullRoom()