Concurrency Fixes (#283)

* Review places where MainActor used

* Adapt to MainActor changes, avoid redundant task detachments

* Move Rust client operations into a dedicated concurrent queue, make init async

* Add changelog

* Fixed small working for awaiting non-async method

* Remove some redundant tasks

* Put back some main actors

* Fix tests

* Fixed timeline updates when the number of items doesn't change. Keeps more previous home screen room data between reloads

Co-authored-by: Stefan Ceriu <stefanc@matrix.org>

ElementX/Sources/Other/SwiftUI/ViewModel/StateStoreViewModel.swift

@@ -96,12 +96,13 @@ class StateStoreViewModel<State: BindableState, ViewAction> {
 
     init(initialViewState: State) {
         context = Context(initialViewState: initialViewState)
-        context.viewActions.sink { [weak self] action in
-            guard let self else { return }
-
-            Task { await self.process(viewAction: action) }
-        }
-        .store(in: &cancellables)
+        context.viewActions
+            .sink { [weak self] action in
+                guard let self else { return }
+
+                Task { await self.process(viewAction: action) }
+            }
+            .store(in: &cancellables)
     }
 
     /// Override to handles incoming `ViewAction`s from the `ViewModel`.

ElementX/Sources/Screens/HomeScreen/HomeScreenViewModel.swift

@@ -23,6 +23,7 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
     private let userSession: UserSessionProtocol
     private let roomSummaryProvider: RoomSummaryProviderProtocol
     private let attributedStringBuilder: AttributedStringBuilderProtocol
+    private var roomsForIdentifiers = [String: HomeScreenRoom]()
 
     var callback: ((HomeScreenViewModelAction) -> Void)?
 
@@ -72,9 +73,7 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
         roomSummaryProvider.roomListPublisher
             .receive(on: DispatchQueue.main)
             .sink { [weak self] _ in
-                Task {
-                    await self?.updateRooms()
-                }
+                self?.updateRooms()
             }
             .store(in: &cancellables)
 
@@ -91,10 +90,8 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
                 state.userDisplayName = userDisplayName
             }
         }
-
-        Task {
-            await updateRooms()
-        }
+
+        updateRooms()
     }
 
     // MARK: - Public
@@ -117,52 +114,58 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
     // MARK: - Private
 
     private func loadDataForRoomIdentifier(_ identifier: String) {
-        guard let summary = roomSummaryProvider.roomListPublisher.value.first(where: { $0.asFilled?.id == identifier })?.asFilled,
-              let homeRoomIndex = state.rooms.firstIndex(where: { $0.id == identifier }) else {
+        guard let roomSummary = roomSummaryProvider.roomListPublisher.value.first(where: { $0.asFilled?.id == identifier })?.asFilled,
+              let roomIndex = state.rooms.firstIndex(where: { $0.id == identifier }) else {
             return
         }
 
-        var details = state.rooms[homeRoomIndex]
+        var room = state.rooms[roomIndex]
 
-        guard details.avatar == nil,
-              let avatarURLString = summary.avatarURLString else {
+        guard room.avatar == nil,
+              let avatarURLString = roomSummary.avatarURLString else {
             return
         }
 
         Task {
             if case let .success(image) = await userSession.mediaProvider.loadImageFromURLString(avatarURLString, avatarSize: .room(on: .home)) {
-                details.avatar = image
-                state.rooms[homeRoomIndex] = details
+                room.avatar = image
+                state.rooms[roomIndex] = room
+                roomsForIdentifiers[roomSummary.id] = room
             }
         }
     }
 
-    private func updateRooms() async {
-        state.rooms = await Task.detached {
-            var rooms = [HomeScreenRoom]()
-
-            for summary in self.roomSummaryProvider.roomListPublisher.value {
-                switch summary {
-                case .empty(let id):
-                    rooms.append(HomeScreenRoom.placeholder(id: id))
-                case .filled(let summary):
-                    let avatarImage = await self.userSession.mediaProvider.imageFromURLString(summary.avatarURLString, avatarSize: .room(on: .home))
-
-                    var timestamp: String?
-                    if let lastMessageTimestamp = summary.lastMessageTimestamp {
-                        timestamp = lastMessageTimestamp.formatted(date: .omitted, time: .shortened)
-                    }
-
-                    rooms.append(HomeScreenRoom(id: summary.id,
-                                                name: summary.name,
-                                                hasUnreads: summary.unreadNotificationCount > 0,
-                                                timestamp: timestamp,
-                                                lastMessage: summary.lastMessage,
-                                                avatar: avatarImage))
+    private func updateRooms() {
+        var rooms = [HomeScreenRoom]()
+        var newRoomsForIdentifiers = [String: HomeScreenRoom]()
+
+        for summary in roomSummaryProvider.roomListPublisher.value {
+            switch summary {
+            case .empty(let id):
+                rooms.append(HomeScreenRoom.placeholder(id: id))
+            case .filled(let summary):
+                let oldRoom = roomsForIdentifiers[summary.id]
+
+                let avatarImage = userSession.mediaProvider.imageFromURLString(summary.avatarURLString, avatarSize: .room(on: .home))
+
+                var timestamp: String?
+                if let lastMessageTimestamp = summary.lastMessageTimestamp {
+                    timestamp = lastMessageTimestamp.formatted(date: .omitted, time: .shortened)
                 }
+
+                let room = HomeScreenRoom(id: summary.id,
+                                          name: summary.name,
+                                          hasUnreads: summary.unreadNotificationCount > 0,
+                                          timestamp: timestamp ?? oldRoom?.timestamp,
+                                          lastMessage: summary.lastMessage ?? oldRoom?.lastMessage,
+                                          avatar: avatarImage ?? oldRoom?.avatar)
+
+                rooms.append(room)
+                newRoomsForIdentifiers[summary.id] = room
             }
-
-            return rooms
-        }.value
+        }
+
+        state.rooms = rooms
+        roomsForIdentifiers = newRoomsForIdentifiers
     }
 }

ElementX/Sources/Screens/RoomScreen/View/TimelineItemList.swift

@@ -152,6 +152,11 @@ struct TimelineItemList: View {
             // Otherwise just update the items
             timelineItems = context.viewState.items
         }
+        .onChange(of: context.viewState.items, perform: { items in
+            if timelineItems != items {
+                timelineItems = items
+            }
+        })
         .background(GeometryReader { geo in
             Color.clear.preference(key: ViewFramePreferenceKey.self, value: [geo.frame(in: .global)])
         })

ElementX/Sources/Services/Authentication/AuthenticationServiceProxyProtocol.swift

@@ -27,7 +27,6 @@ enum AuthenticationServiceError: Error {
     case failedLoggingIn
 }
 
-@MainActor
 protocol AuthenticationServiceProxyProtocol {
     var homeserver: LoginHomeserver { get }
 

ElementX/Sources/Services/Background/BackgroundTaskServiceProtocol.swift

@@ -16,6 +16,7 @@
 
 import Foundation
 
+@MainActor
 protocol BackgroundTaskServiceProtocol {
     func startBackgroundTask(withName name: String,
                              isReusable: Bool,