refactor(mobile): introduce image request registry on iOS (#27486)

* refactor: replace DispatchQueue + DispatchSemaphore with OperationQueue for image processing

* implement RequestRegistry and UnfairLock for managing cancellable requests

* implement requests registry for local and remote image processing

* remove Cancellable protocol and cancel method from request registry

* use mutex

---------

Co-authored-by: mertalev <101130780+mertalev@users.noreply.github.com>

mobile/ios/Runner.xcodeproj/project.pbxproj

@@ -3,7 +3,7 @@
 	archiveVersion = 1;
 	classes = {
 	};
-	objectVersion = 54;
+	objectVersion = 77;
 	objects = {
 
 /* Begin PBXBuildFile section */
@@ -16,6 +16,7 @@
 		97C146FC1CF9000F007C117D /* Main.storyboard in Resources */ = {isa = PBXBuildFile; fileRef = 97C146FA1CF9000F007C117D /* Main.storyboard */; };
 		97C146FE1CF9000F007C117D /* Assets.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = 97C146FD1CF9000F007C117D /* Assets.xcassets */; };
 		97C147011CF9000F007C117D /* LaunchScreen.storyboard in Resources */ = {isa = PBXBuildFile; fileRef = 97C146FF1CF9000F007C117D /* LaunchScreen.storyboard */; };
+		A01DD69B2F7F43B40049AB63 /* ImageRequest.swift in Sources */ = {isa = PBXBuildFile; fileRef = A01DD6982F7F43B40049AB63 /* ImageRequest.swift */; };
 		B21E34AA2E5AFD2B0031FDB9 /* BackgroundWorkerApiImpl.swift in Sources */ = {isa = PBXBuildFile; fileRef = B21E34A92E5AFD210031FDB9 /* BackgroundWorkerApiImpl.swift */; };
 		B21E34AC2E5B09190031FDB9 /* BackgroundWorker.swift in Sources */ = {isa = PBXBuildFile; fileRef = B21E34AB2E5B09100031FDB9 /* BackgroundWorker.swift */; };
 		B25D377A2E72CA15008B6CA7 /* Connectivity.g.swift in Sources */ = {isa = PBXBuildFile; fileRef = B25D37782E72CA15008B6CA7 /* Connectivity.g.swift */; };
@@ -102,6 +103,7 @@
 		97C146FD1CF9000F007C117D /* Assets.xcassets */ = {isa = PBXFileReference; lastKnownFileType = folder.assetcatalog; path = Assets.xcassets; sourceTree = "<group>"; };
 		97C147001CF9000F007C117D /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.storyboard; name = Base; path = Base.lproj/LaunchScreen.storyboard; sourceTree = "<group>"; };
 		97C147021CF9000F007C117D /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
+		A01DD6982F7F43B40049AB63 /* ImageRequest.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ImageRequest.swift; sourceTree = "<group>"; };
 		B1FBA9EE014DE20271B0FE77 /* Pods-ShareExtension.profile.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-ShareExtension.profile.xcconfig"; path = "Target Support Files/Pods-ShareExtension/Pods-ShareExtension.profile.xcconfig"; sourceTree = "<group>"; };
 		B21E34A92E5AFD210031FDB9 /* BackgroundWorkerApiImpl.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BackgroundWorkerApiImpl.swift; sourceTree = "<group>"; };
 		B21E34AB2E5B09100031FDB9 /* BackgroundWorker.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BackgroundWorker.swift; sourceTree = "<group>"; };
@@ -137,20 +139,23 @@
 			);
 			target = F0B57D372DF764BD00DC5BCC /* WidgetExtension */;
 		};
+		FE1BB4572F83196E0087DBF9 /* Exceptions for "Utility" folder in "Runner" target */ = {
+			isa = PBXFileSystemSynchronizedBuildFileExceptionSet;
+			membershipExceptions = (
+				Mutex.swift,
+			);
+			target = 97C146ED1CF9000F007C117D /* Runner */;
+		};
 /* End PBXFileSystemSynchronizedBuildFileExceptionSet section */
 
 /* Begin PBXFileSystemSynchronizedRootGroup section */
 		B231F52D2E93A44A00BC45D1 /* Core */ = {
 			isa = PBXFileSystemSynchronizedRootGroup;
-			exceptions = (
-			);
 			path = Core;
 			sourceTree = "<group>";
 		};
 		B2CF7F8C2DDE4EBB00744BF6 /* Sync */ = {
 			isa = PBXFileSystemSynchronizedRootGroup;
-			exceptions = (
-			);
 			path = Sync;
 			sourceTree = "<group>";
 		};
@@ -162,10 +167,16 @@
 			path = WidgetExtension;
 			sourceTree = "<group>";
 		};
-		FEE084F22EC172080045228E /* Schemas */ = {
+		FE1BB4562F8319560087DBF9 /* Utility */ = {
 			isa = PBXFileSystemSynchronizedRootGroup;
 			exceptions = (
+				FE1BB4572F83196E0087DBF9 /* Exceptions for "Utility" folder in "Runner" target */,
 			);
+			path = Utility;
+			sourceTree = "<group>";
+		};
+		FEE084F22EC172080045228E /* Schemas */ = {
+			isa = PBXFileSystemSynchronizedRootGroup;
 			path = Schemas;
 			sourceTree = "<group>";
 		};
@@ -273,6 +284,7 @@
 		97C146F01CF9000F007C117D /* Runner */ = {
 			isa = PBXGroup;
 			children = (
+				FE1BB4562F8319560087DBF9 /* Utility */,
 				FEE084F22EC172080045228E /* Schemas */,
 				B231F52D2E93A44A00BC45D1 /* Core */,
 				B25D37792E72CA15008B6CA7 /* Connectivity */,
@@ -327,6 +339,7 @@
 		FED3B1952E253E9B0030FD97 /* Images */ = {
 			isa = PBXGroup;
 			children = (
+				A01DD6982F7F43B40049AB63 /* ImageRequest.swift */,
 				FE5FE4AD2F30FBC000A71243 /* ImageProcessing.swift */,
 				FE5499F72F1198DE006016CB /* RemoteImagesImpl.swift */,
 				FE5499F52F11980E006016CB /* LocalImagesImpl.swift */,
@@ -558,10 +571,14 @@
 			inputFileListPaths = (
 				"${PODS_ROOT}/Target Support Files/Pods-Runner/Pods-Runner-resources-${CONFIGURATION}-input-files.xcfilelist",
 			);
+			inputPaths = (
+			);
 			name = "[CP] Copy Pods Resources";
 			outputFileListPaths = (
 				"${PODS_ROOT}/Target Support Files/Pods-Runner/Pods-Runner-resources-${CONFIGURATION}-output-files.xcfilelist",
 			);
+			outputPaths = (
+			);
 			runOnlyForDeploymentPostprocessing = 0;
 			shellPath = /bin/sh;
 			shellScript = "\"${PODS_ROOT}/Target Support Files/Pods-Runner/Pods-Runner-resources.sh\"\n";
@@ -590,10 +607,14 @@
 			inputFileListPaths = (
 				"${PODS_ROOT}/Target Support Files/Pods-Runner/Pods-Runner-frameworks-${CONFIGURATION}-input-files.xcfilelist",
 			);
+			inputPaths = (
+			);
 			name = "[CP] Embed Pods Frameworks";
 			outputFileListPaths = (
 				"${PODS_ROOT}/Target Support Files/Pods-Runner/Pods-Runner-frameworks-${CONFIGURATION}-output-files.xcfilelist",
 			);
+			outputPaths = (
+			);
 			runOnlyForDeploymentPostprocessing = 0;
 			shellPath = /bin/sh;
 			shellScript = "\"${PODS_ROOT}/Target Support Files/Pods-Runner/Pods-Runner-frameworks.sh\"\n";
@@ -608,6 +629,7 @@
 			files = (
 				65F32F31299BD2F800CE9261 /* BackgroundServicePlugin.swift in Sources */,
 				74858FAF1ED2DC5600515810 /* AppDelegate.swift in Sources */,
+				A01DD69B2F7F43B40049AB63 /* ImageRequest.swift in Sources */,
 				B21E34AC2E5B09190031FDB9 /* BackgroundWorker.swift in Sources */,
 				FE5499F32F1197D8006016CB /* LocalImages.g.swift in Sources */,
 				FE5499F62F11980E006016CB /* LocalImagesImpl.swift in Sources */,

mobile/ios/Runner/Images/ImageRequest.swift

@@ -0,0 +1,14 @@
+import Foundation
+
+struct RequestRegistry<T: AnyObject & Sendable>: ~Copyable, Sendable {
+  private let requests = Mutex<[Int64: T]>([:])
+
+  func add(requestId: Int64, request: T) {
+    requests.withLock { $0[requestId] = request }
+  }
+
+  @discardableResult
+  func remove(requestId: Int64) -> T? {
+    requests.withLock { $0.removeValue(forKey: requestId) }
+  }
+}

mobile/ios/Runner/Images/LocalImagesImpl.swift

@@ -11,6 +11,11 @@ class LocalImageRequest {
   init(callback: @escaping (Result<[String: Int64]?, any Error>) -> Void) {
     self.callback = callback
   }
+
+  func cancel() {
+    isCancelled = true
+    operation?.cancel()
+  }
 }
 
 class LocalImageApiImpl: LocalImageApi {
@@ -31,9 +36,7 @@ class LocalImageApiImpl: LocalImageApi {
     return requestOptions
   }()
 
-  private static let assetQueue = DispatchQueue(label: "thumbnail.assets", qos: .userInitiated)
+  private static let registry = RequestRegistry<LocalImageRequest>()
-  private static let requestQueue = DispatchQueue(label: "thumbnail.requests", qos: .userInitiated)
-  private static let cancelQueue = DispatchQueue(label: "thumbnail.cancellation", qos: .default)
 
   private static var rgbaFormat = vImage_CGImageFormat(
     bitsPerComponent: 8,
@@ -42,7 +45,6 @@ class LocalImageApiImpl: LocalImageApi {
     bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue),
     renderingIntent: .defaultIntent
   )!
-  private static var requests = [Int64: LocalImageRequest]()
   private static let assetCache = {
     let assetCache = NSCache<NSString, PHAsset>()
     assetCache.countLimit = 10000
@@ -73,7 +75,7 @@ class LocalImageApiImpl: LocalImageApi {
 
       guard let asset = Self.requestAsset(assetId: assetId)
       else {
-        Self.remove(requestId: requestId)
+        Self.registry.remove(requestId: requestId)
         completion(.failure(PigeonError(code: "", message: "Could not get asset data for \(assetId)", details: nil)))
         return
       }
@@ -98,12 +100,11 @@ class LocalImageApiImpl: LocalImageApi {
         )
 
         if request.isCancelled {
-          Self.remove(requestId: requestId)
           return completion(ImageProcessing.cancelledResult)
         }
 
         guard let data = imageData else {
-          Self.remove(requestId: requestId)
+          Self.registry.remove(requestId: requestId)
           return completion(.failure(PigeonError(code: "", message: "Could not get image data for \(assetId)", details: nil)))
         }
 
@@ -113,7 +114,6 @@ class LocalImageApiImpl: LocalImageApi {
 
         if request.isCancelled {
           free(pointer)
-          Self.remove(requestId: requestId)
           return completion(ImageProcessing.cancelledResult)
         }
 
@@ -121,7 +121,7 @@ class LocalImageApiImpl: LocalImageApi {
           "pointer": Int64(Int(bitPattern: pointer)),
           "length": Int64(length),
         ]))
-        Self.remove(requestId: requestId)
+        Self.registry.remove(requestId: requestId)
         return
       }
 
@@ -142,7 +142,7 @@ class LocalImageApiImpl: LocalImageApi {
 
       guard let image = image,
             let cgImage = image.cgImage else {
-        Self.remove(requestId: requestId)
+        Self.registry.remove(requestId: requestId)
         return completion(.failure(PigeonError(code: "", message: "Could not get pixel data for \(assetId)", details: nil)))
       }
 
@@ -162,51 +162,32 @@ class LocalImageApiImpl: LocalImageApi {
           "pointer": Int64(Int(bitPattern: buffer.data)),
           "width": Int64(buffer.width),
           "height": Int64(buffer.height),
-          "rowBytes": Int64(buffer.rowBytes)
+          "rowBytes": Int64(buffer.rowBytes),
         ]))
-        Self.remove(requestId: requestId)
+        Self.registry.remove(requestId: requestId)
       } catch {
-        Self.remove(requestId: requestId)
+        Self.registry.remove(requestId: requestId)
         return completion(.failure(PigeonError(code: "", message: "Failed to convert image for \(assetId): \(error)", details: nil)))
       }
     }
 
     request.operation = operation
-    Self.add(requestId: requestId, request: request)
+    Self.registry.add(requestId: requestId, request: request)
     ImageProcessing.queue.addOperation(operation)
   }
 
   func cancelRequest(requestId: Int64) {
-    Self.cancel(requestId: requestId)
+    Self.registry.remove(requestId: requestId)?.cancel()
-  }
-
-  private static func add(requestId: Int64, request: LocalImageRequest) -> Void {
-    requestQueue.sync { requests[requestId] = request }
-  }
-
-  private static func remove(requestId: Int64) -> Void {
-    requestQueue.sync { requests[requestId] = nil }
-  }
-
-  private static func cancel(requestId: Int64) -> Void {
-    requestQueue.async {
-      guard let request = requests.removeValue(forKey: requestId) else { return }
-      request.isCancelled = true
-      guard let operation = request.operation else { return }
-      if operation.isCancelled {
-        cancelQueue.async { request.callback(ImageProcessing.cancelledResult) }
-      }
-    }
   }
 
   private static func requestAsset(assetId: String) -> PHAsset? {
-    var asset: PHAsset?
+    if let cached = assetCache.object(forKey: assetId as NSString) {
-    assetQueue.sync { asset = assetCache.object(forKey: assetId as NSString) }
+      return cached
-    if asset != nil { return asset }
+    }
 
     guard let asset = PHAsset.fetchAssets(withLocalIdentifiers: [assetId], options: Self.fetchOptions).firstObject
     else { return nil }
-    assetQueue.async { assetCache.setObject(asset, forKey: assetId as NSString) }
+    assetCache.setObject(asset, forKey: assetId as NSString)
     return asset
   }
 }

mobile/ios/Runner/Images/RemoteImagesImpl.swift

@@ -14,11 +14,15 @@ class RemoteImageRequest {
     self.task = task
     self.completion = completion
   }
+
+  func cancel() {
+    isCancelled = true
+    task?.cancel()
+  }
 }
 
 class RemoteImageApiImpl: NSObject, RemoteImageApi {
-  private static var lock = os_unfair_lock()
+  private static let registry = RequestRegistry<RemoteImageRequest>()
-  private static var requests = [Int64: RemoteImageRequest]()
   private static var rgbaFormat = vImage_CGImageFormat(
     bitsPerComponent: 8,
     bitsPerPixel: 32,
@@ -43,20 +47,15 @@ class RemoteImageApiImpl: NSObject, RemoteImageApi {
 
     let request = RemoteImageRequest(id: requestId, task: task, completion: completion)
 
-    os_unfair_lock_lock(&Self.lock)
+    Self.registry.add(requestId: requestId, request: request)
-    Self.requests[requestId] = request
-    os_unfair_lock_unlock(&Self.lock)
 
     task.resume()
   }
 
   private static func handleCompletion(requestId: Int64, encoded: Bool, data: Data?, response: URLResponse?, error: Error?) {
-    os_unfair_lock_lock(&Self.lock)
+    guard let request = registry.remove(requestId: requestId) else {
-    guard let request = requests[requestId] else {
+      return
-      return os_unfair_lock_unlock(&Self.lock)
     }
-    requests[requestId] = nil
-    os_unfair_lock_unlock(&Self.lock)
 
     if let error = error {
       if request.isCancelled || (error as NSError).code == NSURLErrorCancelled {
@@ -127,13 +126,7 @@ class RemoteImageApiImpl: NSObject, RemoteImageApi {
   }
 
   func cancelRequest(requestId: Int64) {
-    os_unfair_lock_lock(&Self.lock)
+    Self.registry.remove(requestId: requestId)?.cancel()
-    let request = Self.requests[requestId]
-    os_unfair_lock_unlock(&Self.lock)
-
-    guard let request = request else { return }
-    request.isCancelled = true
-    request.task?.cancel()
   }
 
   func clearCache(completion: @escaping (Result<Int64, any Error>) -> Void) {

mobile/ios/Runner/Utility/Mutex.swift

@@ -0,0 +1,54 @@
+import Darwin
+
+// Can be replaced with std Mutex when the deployment target is iOS 18+
+struct Mutex<Value: ~Copyable>: ~Copyable, @unchecked Sendable {
+  struct _Buffer: ~Copyable {
+    var lock: os_unfair_lock = .init()
+    var value: Value
+
+    init(value: consuming Value) {
+      self.value = value
+    }
+
+    deinit {}
+  }
+
+  let _buffer: UnsafeMutablePointer<_Buffer>
+
+  init(_ initialValue: consuming sending Value) {
+    _buffer = .allocate(capacity: 1)
+    _buffer.initialize(to: _Buffer(value: initialValue))
+  }
+
+  deinit {
+    _buffer.deinitialize(count: 1)
+    _buffer.deallocate()
+  }
+
+  @discardableResult
+  borrowing func withLock<Result: ~Copyable, E: Error>(
+    _ body: (inout sending Value) throws(E) -> sending Result
+  ) throws(E) -> sending Result {
+    os_unfair_lock_lock(&_buffer.pointee.lock)
+    defer { os_unfair_lock_unlock(&_buffer.pointee.lock) }
+    return try body(&_buffer.pointee.value)
+  }
+}
+
+// Can be replaced with OSAllocatedUnfairLock when the deployment target is iOS 16+
+typealias UnfairLock = Mutex<Void>
+
+extension Mutex where Value == Void {
+  init() {
+    self.init(())
+  }
+
+  @discardableResult
+  borrowing func withLock<Result: ~Copyable, E: Error>(
+    _ body: () throws(E) -> sending Result
+  ) throws(E) -> sending Result {
+    os_unfair_lock_lock(&_buffer.pointee.lock)
+    defer { os_unfair_lock_unlock(&_buffer.pointee.lock) }
+    return try body()
+  }
+}