improve camera detection. Better support for cancellations.

Author: stevensJourney

Demo/PowerSyncExample/Components/TodoListView.swift

@@ -173,7 +173,13 @@ struct TodoListView: View {
     private func checkCameraAvailability() {
         // https://developer.apple.com/forums/thread/748448
         // On MacOS MetalAPI validation needs to be disabled
+
+#if targetEnvironment(simulator)
+        // Camera does not work on the simulator
+        isCameraAvailable = false
+#else
         isCameraAvailable = UIImagePickerController.isSourceTypeAvailable(.camera)
+#endif
     }
 }
 

Sources/PowerSync/Kotlin/KotlinPowerSyncDatabaseImpl.swift

@@ -192,7 +192,13 @@ final class KotlinPowerSyncDatabaseImpl: PowerSyncDatabaseProtocol {
             let task = Task {
                 do {
                     var mapperError: Error?
-
+                    // HACK!
+                    // SKIEE doesn't support custom exceptions in Flows
+                    // Exceptions which occur in the Flow itself cause runtime crashes.
+                    // The most probable crash would be the internal EXPLAIN statement.
+                    // This attempts to EXPLAIN the query before passing it to Kotlin
+                    // We could introduce an onChange API in Kotlin which we use to implement watches here.
+                    // This would prevent most issues with exceptions.
                     // EXPLAIN statement to prevent crashes in SKIEE
                     _ = try await self.kotlinDatabase.getAll(
                         sql: "EXPLAIN \(options.sql)",
@@ -210,7 +216,7 @@ final class KotlinPowerSyncDatabaseImpl: PowerSyncDatabaseProtocol {
                                 return try options.mapper(cursor)
                             } catch {
                                 mapperError = error
-                                return nil as RowType?
+                                return ()
                             }
                         }
                     ) {

Sources/PowerSync/attachments/AttachmentQueue.swift

@@ -133,7 +133,7 @@ public class AttachmentQueue {
             }
 
             // Verify initial state
-            try await attachmentsService.withLock { context in
+            try await attachmentsService.withContext { context in
                 try await self.verifyAttachments(context: context)
             }
 
@@ -146,6 +146,7 @@ public class AttachmentQueue {
                         group.addTask {
                             var previousConnected = self.db.currentStatus.connected
                             for await status in self.db.currentStatus.asFlow() {
+                                try Task.checkCancellation()
                                 if !previousConnected && status.connected {
                                     try await self.syncingService.triggerSync()
                                 }
@@ -223,7 +224,7 @@ public class AttachmentQueue {
     public func processWatchedAttachments(items: [WatchedAttachmentItem]) async throws {
         // Need to get all the attachments which are tracked in the DB.
         // We might need to restore an archived attachment.
-        try await attachmentsService.withLock { context in
+        try await attachmentsService.withContext { context in
             let currentAttachments = try await context.getAttachments()
             var attachmentUpdates = [Attachment]()
 
@@ -316,7 +317,7 @@ public class AttachmentQueue {
         // Write the file to the filesystem
         let fileSize = try await localStorage.saveFile(filePath: localUri, data: data)
 
-        return try await attachmentsService.withLock { context in
+        return try await attachmentsService.withContext { context in
             // Start a write transaction. The attachment record and relevant local relationship
             // assignment should happen in the same transaction.
             try await self.db.writeTransaction { tx in
@@ -346,12 +347,11 @@ public class AttachmentQueue {
         attachmentId: String,
         updateHook: @escaping (ConnectionContext, Attachment) throws -> Void
     ) async throws -> Attachment {
-        try await attachmentsService.withLock { context in
+        try await attachmentsService.withContext { context in
             guard let attachment = try await context.getAttachment(id: attachmentId) else {
                 throw PowerSyncAttachmentError.notFound("Attachment record with id \(attachmentId) was not found.")
             }
 
-            self.logger.debug("Marking attachment as deleted", tag: nil)
             let result = try await self.db.writeTransaction { tx in
                 try updateHook(tx, attachment)
 
@@ -367,7 +367,6 @@ public class AttachmentQueue {
 
                 return try context.upsertAttachment(updatedAttachment, context: tx)
             }
-            self.logger.debug("Marked attachment as deleted", tag: nil)
             return result
         }
     }
@@ -381,7 +380,7 @@ public class AttachmentQueue {
 
     /// Removes all archived items
     public func expireCache() async throws {
-        try await attachmentsService.withLock { context in
+        try await attachmentsService.withContext { context in
             var done = false
             repeat {
                 done = try await self.syncingService.deleteArchivedAttachments(context)
@@ -391,7 +390,7 @@ public class AttachmentQueue {
 
     /// Clears the attachment queue and deletes all attachment files
     public func clearQueue() async throws {
-        try await attachmentsService.withLock { context in
+        try await attachmentsService.withContext { context in
             try await context.clearQueue()
             // Remove the attachments directory
             try await self.localStorage.rmDir(path: self.attachmentsDirectory)

Sources/PowerSync/attachments/AttachmentService.swift

@@ -57,7 +57,7 @@ public class AttachmentService {
     }
 
     /// Executes a callback with exclusive access to the attachment context.
-    public func withLock<R>(callback: @Sendable @escaping (AttachmentContext) async throws -> R) async throws -> R {
+    public func withContext<R>(callback: @Sendable @escaping (AttachmentContext) async throws -> R) async throws -> R {
         try await lock.withLock {
             try await callback(context)
         }

Sources/PowerSync/attachments/LockActor.swift

@@ -1,24 +1,46 @@
+import Foundation
 
-internal actor LockActor {
+actor LockActor {
     private var isLocked = false
-    private var queue: [CheckedContinuation<Void, Never>] = []
-    
-    func withLock<T>(_ execute: @Sendable () async throws -> T) async throws -> T {
-        if isLocked {
+    private var waiters: [(id: UUID, continuation: CheckedContinuation<Void, Never>)] = []
+
+    func withLock<T>(_ operation: @Sendable () async throws -> T) async throws -> T {
+        try await waitUntilUnlocked()
+
+        isLocked = true
+        defer { unlockNext() }
+
+        try Task.checkCancellation() // cancellation check after acquiring lock
+        return try await operation()
+    }
+
+    private func waitUntilUnlocked() async throws {
+        if !isLocked { return }
+
+        let id = UUID()
+
+        // Use withTaskCancellationHandler to manage cancellation
+        await withTaskCancellationHandler {
             await withCheckedContinuation { continuation in
-                queue.append(continuation)
+                waiters.append((id: id, continuation: continuation))
+            }
+        } onCancel: {
+            // Cancellation logic: remove the waiter when cancelled
+            Task {
+                await self.removeWaiter(id: id)
             }
         }
-    
-        isLocked = true
-        defer { unlockNext() }
-        return try await execute()
+    }
+
+    private func removeWaiter(id: UUID) async {
+        // Safely remove the waiter from the actor's waiters list
+        waiters.removeAll { $0.id == id }
     }
 
     private func unlockNext() {
-        if let next = queue.first {
-            queue.removeFirst()
-            next.resume(returning: ())
+        if let next = waiters.first {
+            waiters.removeFirst()
+            next.continuation.resume()
         } else {
             isLocked = false
         }

Sources/PowerSync/attachments/SyncingService.swift

@@ -155,7 +155,7 @@ public class SyncingService {
                         for await _ in syncTrigger {
                             try Task.checkCancellation()
 
-                            try await self.attachmentsService.withLock { context in
+                            try await self.attachmentsService.withContext { context in
                                 let attachments = try await context.getActiveAttachments()
                                 try await self.handleSync(context: context, attachments: attachments)
                                 _ = try await self.deleteArchivedAttachments(context)