Various performance tweaks (#474)

* Store and reuse room list placeholder avatars and last messages

* Cache and reuse HomeScreenRooms

* Reduce RoomSummaryProvider diff collection time

* Promote more logs to info

* Slighty tweak RustTracing to make it easier to configure

* Move TimelineProvider and RoomTimelineController item processing to background queues

* Prevent the timeline from stopping an ogoing decelerating scroll when starting backpaginating

ElementX/Sources/Services/Timeline/RoomTimelineProvider.swift

@@ -29,6 +29,7 @@ private class RoomTimelineListener: TimelineListener {
 class RoomTimelineProvider: RoomTimelineProviderProtocol {
     private let roomProxy: RoomProxyProtocol
     private var cancellables = Set<AnyCancellable>()
+    private let serialDispatchQueue: DispatchQueue
     
     let itemsPublisher = CurrentValueSubject<[TimelineItemProxy], Never>([])
     
@@ -40,6 +41,7 @@ class RoomTimelineProvider: RoomTimelineProviderProtocol {
     
     init(roomProxy: RoomProxyProtocol) {
         self.roomProxy = roomProxy
+        serialDispatchQueue = DispatchQueue(label: "io.element.elementx.roomtimelineprovider")
         itemProxies = []
 
         Task {
@@ -47,8 +49,8 @@ class RoomTimelineProvider: RoomTimelineProviderProtocol {
             
             roomTimelineListener
                 .itemsUpdatePublisher
-                .receive(on: DispatchQueue.main)
-                .sink { [weak self] in self?.updateItemsWithDiff($0) }
+                .collect(.byTime(serialDispatchQueue, 0.025))
+                .sink { [weak self] in self?.updateItemsWithDiffs($0) }
                 .store(in: &cancellables)
             
             switch await roomProxy.addTimelineListener(listener: roomTimelineListener) {
@@ -63,22 +65,25 @@ class RoomTimelineProvider: RoomTimelineProviderProtocol {
     
     // MARK: - Private
     
-    private func updateItemsWithDiff(_ diff: TimelineDiff) {
+    private func updateItemsWithDiffs(_ diffs: [TimelineDiff]) {
         MXLog.verbose("Received timeline diff")
         
-        guard let collectionDiff = buildDiff(from: diff, on: itemProxies) else {
-            MXLog.error("Failed building CollectionDifference from \(diff)")
-            return
-        }
-        
-        guard let updatedItems = itemProxies.applying(collectionDiff) else {
-            MXLog.error("Failed applying diff: \(collectionDiff)")
-            return
-        }
-        
-        MXLog.verbose("Applied diff \(collectionDiff), new count: \(updatedItems.count)")
-        
-        itemProxies = updatedItems
+        itemProxies = diffs
+            .reduce(itemProxies) { currentItems, diff in
+                guard let collectionDiff = buildDiff(from: diff, on: currentItems) else {
+                    MXLog.error("Failed building CollectionDifference from \(diff)")
+                    return currentItems
+                }
+                
+                guard let updatedItems = currentItems.applying(collectionDiff) else {
+                    MXLog.error("Failed applying diff: \(collectionDiff)")
+                    return currentItems
+                }
+                
+                MXLog.verbose("Applied diff \(collectionDiff), new count: \(updatedItems.count)")
+                
+                return updatedItems
+            }
         
         MXLog.verbose("Finished applying diff")
     }

ElementX/Sources/Services/Timeline/TimelineController/RoomTimelineController.swift

@@ -21,10 +21,11 @@ import UniformTypeIdentifiers
 
 class RoomTimelineController: RoomTimelineControllerProtocol {
     private let userId: String
+    private let roomProxy: RoomProxyProtocol
     private let timelineProvider: RoomTimelineProviderProtocol
     private let timelineItemFactory: RoomTimelineItemFactoryProtocol
     private let mediaProvider: MediaProviderProtocol
-    let roomProxy: RoomProxyProtocol
+    private let serialDispatchQueue: DispatchQueue
     
     private var cancellables = Set<AnyCancellable>()
     private var timelineItemsUpdateTask: Task<Void, Never>? {
@@ -51,10 +52,11 @@ class RoomTimelineController: RoomTimelineControllerProtocol {
         self.timelineItemFactory = timelineItemFactory
         self.mediaProvider = mediaProvider
         self.roomProxy = roomProxy
+        serialDispatchQueue = DispatchQueue(label: "io.element.elementx.roomtimelineprovider")
         
         self.timelineProvider
             .itemsPublisher
-            .receive(on: DispatchQueue.main)
+            .receive(on: serialDispatchQueue)
             .sink { [weak self] _ in
                 guard let self else { return }
                 
@@ -236,14 +238,8 @@ class RoomTimelineController: RoomTimelineControllerProtocol {
         updateTimelineItems()
     }
     
-    private func updateTimelineItems() {
-        timelineItemsUpdateTask = Task {
-            await asyncUpdateTimelineItems()
-        }
-    }
-    
     // swiftlint:disable:next cyclomatic_complexity
-    private func asyncUpdateTimelineItems() async {
+    private func updateTimelineItems() {
         var newTimelineItems = [RoomTimelineItemProtocol]()
         var canBackPaginate = true
         var isBackPaginating = false