[Background Mapping] Avoid crash when accessing DTOs while DB is bein…

…g recreated (#2934) * Make sure the object is valid before mapping it * Keep track of DB being deleted on BackgroundDatabaseObserver * Improve API to track if database is being removed --------- Co-authored-by: Pol Quintana <[email protected]>
GetStream · Dec 13, 2023 · e6079f9 · e6079f9
1 parent f8bdc61
commit e6079f9
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Showing 2 changed files with 36 additions and 10 deletions.
diff --git a/Sources/StreamChat/Controllers/DatabaseObserver/BackgroundDatabaseObserver.swift b/Sources/StreamChat/Controllers/DatabaseObserver/BackgroundDatabaseObserver.swift
@@ -39,14 +39,14 @@ class BackgroundDatabaseObserver<Item, DTO: NSManagedObject> {
 
     private var _isInitialized: Bool = false
     private var isInitialized: Bool {
-        get {
-            queue.sync { _isInitialized }
-        }
-        set {
-            queue.async(flags: .barrier) {
-                self._isInitialized = newValue
-            }
-        }
+        get { queue.sync { _isInitialized } }
+        set { queue.async(flags: .barrier) { self._isInitialized = newValue } }
+    }
+
+    private var _isDeletingDatabase: Bool = false
+    private var isDeletingDatabase: Bool {
+        get { queue.sync { _isDeletingDatabase }}
+        set { queue.async(flags: .barrier) { self._isDeletingDatabase = newValue } }
     }
 
     deinit {
@@ -104,7 +104,7 @@ class BackgroundDatabaseObserver<Item, DTO: NSManagedObject> {
     /// Starts observing the changes in the database.
     /// - Throws: An error if the fetch  fails.
     func startObserving() throws {
-        guard !isInitialized else { return }
+        guard !isInitialized && !isDeletingDatabase else { return }
         isInitialized = true
 
         do {
@@ -191,7 +191,8 @@ class BackgroundDatabaseObserver<Item, DTO: NSManagedObject> {
 
         var items: [Item?] = []
         items = objects.map { [weak self] in
-            try? self?.itemCreator($0)
+            guard self?.isDeletingDatabase == false else { return nil }
+            return try? self?.itemCreator($0)
         }
 
         let sorting = self.sorting
@@ -213,6 +214,11 @@ extension BackgroundDatabaseObserver: DatabaseObserverRemovalListener {
             isBackground: true,
             frc: frc,
             changeAggregator: changeAggregator,
+            onStart: { [weak self] in
+                self?.queue.async(flags: .barrier) {
+                    self?._isDeletingDatabase = true
+                }
+            },
             onItemsRemoval: { [weak self] completion in
                 self?.queue.async(flags: .barrier) {
                     self?._items = []
@@ -224,6 +230,7 @@ extension BackgroundDatabaseObserver: DatabaseObserverRemovalListener {
             onCompletion: { [weak self] in
                 guard let self = self else { return }
                 self.queue.async(flags: .barrier) {
+                    self._isDeletingDatabase = false
                     self._isInitialized = false
 
                     DispatchQueue.main.async {

diff --git a/Sources/StreamChat/Controllers/DatabaseObserver/DatabaseObserverRemovalListener.swift b/Sources/StreamChat/Controllers/DatabaseObserver/DatabaseObserverRemovalListener.swift
@@ -14,6 +14,7 @@ extension DatabaseObserverRemovalListener {
         isBackground: Bool,
         frc: NSFetchedResultsController<DTO>,
         changeAggregator: ListChangeAggregator<DTO, Item>,
+        onStart: @escaping () -> Void,
         onItemsRemoval: @escaping (@escaping () -> Void) -> Void,
         onCompletion: @escaping () -> Void
     ) {
@@ -30,6 +31,7 @@ extension DatabaseObserverRemovalListener {
         ) { [weak frc, weak context, weak changeAggregator] _ in
             guard let frc = frc, let context = context, let changeAggregator = changeAggregator else { return }
             guard let fetchResultsController = frc as? NSFetchedResultsController<NSFetchRequestResult> else { return }
+            onStart()
 
             let removeItems = {
                 // Simulate ChangeObserver callbacks like all data are being removed
@@ -76,4 +78,21 @@ extension DatabaseObserverRemovalListener {
             notificationCenter?.removeObserver(didRemoveAllDataNotificationObserver)
         }
     }
+
+    func listenForRemoveAllDataNotifications<Item, DTO: NSManagedObject>(
+        isBackground: Bool,
+        frc: NSFetchedResultsController<DTO>,
+        changeAggregator: ListChangeAggregator<DTO, Item>,
+        onItemsRemoval: @escaping (@escaping () -> Void) -> Void,
+        onCompletion: @escaping () -> Void
+    ) {
+        listenForRemoveAllDataNotifications(
+            isBackground: isBackground,
+            frc: frc,
+            changeAggregator: changeAggregator,
+            onStart: {},
+            onItemsRemoval: onItemsRemoval,
+            onCompletion: onCompletion
+        )
+    }
 }