remove timer

handle missing asset

mobile/ios/Runner.xcodeproj/project.pbxproj

@@ -29,9 +29,11 @@
 		FAC6F89B2D287C890078CB2F /* ShareExtension.appex in Embed Foundation Extensions */ = {isa = PBXBuildFile; fileRef = FAC6F8902D287C890078CB2F /* ShareExtension.appex */; settings = {ATTRIBUTES = (RemoveHeadersOnCopy, ); }; };
 		FAC6F8B72D287F120078CB2F /* ShareViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = FAC6F8B52D287F120078CB2F /* ShareViewController.swift */; };
 		FAC6F8B92D287F120078CB2F /* MainInterface.storyboard in Resources */ = {isa = PBXBuildFile; fileRef = FAC6F8B32D287F120078CB2F /* MainInterface.storyboard */; };
-		FEAFA8732E4D42F4001E47FE /* Thumbhash.swift in Sources */ = {isa = PBXBuildFile; fileRef = FEAFA8722E4D42F4001E47FE /* Thumbhash.swift */; };
-		FED3B1962E253E9B0030FD97 /* ThumbnailsImpl.swift in Sources */ = {isa = PBXBuildFile; fileRef = FED3B1942E253E9B0030FD97 /* ThumbnailsImpl.swift */; };
-		FED3B1972E253E9B0030FD97 /* Thumbnails.g.swift in Sources */ = {isa = PBXBuildFile; fileRef = FED3B1932E253E9B0030FD97 /* Thumbnails.g.swift */; };
+		FEC340D12E7326630050078A /* AssetResolver.swift in Sources */ = {isa = PBXBuildFile; fileRef = FEC340C92E7326630050078A /* AssetResolver.swift */; };
+		FEC340D22E7326630050078A /* Thumbhash.swift in Sources */ = {isa = PBXBuildFile; fileRef = FEC340CB2E7326630050078A /* Thumbhash.swift */; };
+		FEC340D32E7326630050078A /* Request.swift in Sources */ = {isa = PBXBuildFile; fileRef = FEC340CF2E7326630050078A /* Request.swift */; };
+		FEC340D42E7326630050078A /* ThumbnailResolver.swift in Sources */ = {isa = PBXBuildFile; fileRef = FEC340CC2E7326630050078A /* ThumbnailResolver.swift */; };
+		FEC340D52E7326630050078A /* Thumbnails.g.swift in Sources */ = {isa = PBXBuildFile; fileRef = FEC340CD2E7326630050078A /* Thumbnails.g.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -115,9 +117,11 @@
 		FAC6F8B42D287F120078CB2F /* ShareExtension.entitlements */ = {isa = PBXFileReference; lastKnownFileType = text.plist.entitlements; path = ShareExtension.entitlements; sourceTree = "<group>"; };
 		FAC6F8B52D287F120078CB2F /* ShareViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ShareViewController.swift; sourceTree = "<group>"; };
 		FAC7416727DB9F5500C668D8 /* RunnerProfile.entitlements */ = {isa = PBXFileReference; lastKnownFileType = text.plist.entitlements; path = RunnerProfile.entitlements; sourceTree = "<group>"; };
-		FEAFA8722E4D42F4001E47FE /* Thumbhash.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Thumbhash.swift; sourceTree = "<group>"; };
-		FED3B1932E253E9B0030FD97 /* Thumbnails.g.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Thumbnails.g.swift; sourceTree = "<group>"; };
-		FED3B1942E253E9B0030FD97 /* ThumbnailsImpl.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ThumbnailsImpl.swift; sourceTree = "<group>"; };
+		FEC340C92E7326630050078A /* AssetResolver.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AssetResolver.swift; sourceTree = "<group>"; };
+		FEC340CB2E7326630050078A /* Thumbhash.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Thumbhash.swift; sourceTree = "<group>"; };
+		FEC340CC2E7326630050078A /* ThumbnailResolver.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ThumbnailResolver.swift; sourceTree = "<group>"; };
+		FEC340CD2E7326630050078A /* Thumbnails.g.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Thumbnails.g.swift; sourceTree = "<group>"; };
+		FEC340CF2E7326630050078A /* Request.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Request.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFileSystemSynchronizedBuildFileExceptionSet section */
@@ -247,6 +251,7 @@
 		97C146F01CF9000F007C117D /* Runner */ = {
 			isa = PBXGroup;
 			children = (
+				FEC340D02E7326630050078A /* Resolvers */,
 				B25D37792E72CA15008B6CA7 /* Connectivity */,
 				B21E34A62E5AF9760031FDB9 /* Background */,
 				B2CF7F8C2DDE4EBB00744BF6 /* Sync */,
@@ -261,7 +266,6 @@
 				1498D2331E8E89220040F4C2 /* GeneratedPluginRegistrant.m */,
 				74858FAE1ED2DC5600515810 /* AppDelegate.swift */,
 				74858FAD1ED2DC5600515810 /* Runner-Bridging-Header.h */,
-				FED3B1952E253E9B0030FD97 /* Images */,
 			);
 			path = Runner;
 			sourceTree = "<group>";
@@ -296,16 +300,34 @@
 			path = ShareExtension;
 			sourceTree = "<group>";
 		};
-		FED3B1952E253E9B0030FD97 /* Images */ = {
+		FEC340CA2E7326630050078A /* Assets */ = {
 			isa = PBXGroup;
 			children = (
-				FEAFA8722E4D42F4001E47FE /* Thumbhash.swift */,
-				FED3B1932E253E9B0030FD97 /* Thumbnails.g.swift */,
-				FED3B1942E253E9B0030FD97 /* ThumbnailsImpl.swift */,
+				FEC340C92E7326630050078A /* AssetResolver.swift */,
+			);
+			path = Assets;
+			sourceTree = "<group>";
+		};
+		FEC340CE2E7326630050078A /* Images */ = {
+			isa = PBXGroup;
+			children = (
+				FEC340CB2E7326630050078A /* Thumbhash.swift */,
+				FEC340CC2E7326630050078A /* ThumbnailResolver.swift */,
+				FEC340CD2E7326630050078A /* Thumbnails.g.swift */,
 			);
 			path = Images;
 			sourceTree = "<group>";
 		};
+		FEC340D02E7326630050078A /* Resolvers */ = {
+			isa = PBXGroup;
+			children = (
+				FEC340CA2E7326630050078A /* Assets */,
+				FEC340CE2E7326630050078A /* Images */,
+				FEC340CF2E7326630050078A /* Request.swift */,
+			);
+			path = Resolvers;
+			sourceTree = "<group>";
+		};
 /* End PBXGroup section */
 
 /* Begin PBXNativeTarget section */
@@ -573,14 +595,16 @@
 				74858FAF1ED2DC5600515810 /* AppDelegate.swift in Sources */,
 				B21E34AC2E5B09190031FDB9 /* BackgroundWorker.swift in Sources */,
 				B25D377A2E72CA15008B6CA7 /* Connectivity.g.swift in Sources */,
-				FEAFA8732E4D42F4001E47FE /* Thumbhash.swift in Sources */,
 				B25D377C2E72CA26008B6CA7 /* ConnectivityApiImpl.swift in Sources */,
-				FED3B1962E253E9B0030FD97 /* ThumbnailsImpl.swift in Sources */,
 				B21E34AA2E5AFD2B0031FDB9 /* BackgroundWorkerApiImpl.swift in Sources */,
-				FED3B1972E253E9B0030FD97 /* Thumbnails.g.swift in Sources */,
 				1498D2341E8E89220040F4C2 /* GeneratedPluginRegistrant.m in Sources */,
 				B2BE315F2E5E5229006EEF88 /* BackgroundWorker.g.swift in Sources */,
 				65F32F33299D349D00CE9261 /* BackgroundSyncWorker.swift in Sources */,
+				FEC340D12E7326630050078A /* AssetResolver.swift in Sources */,
+				FEC340D22E7326630050078A /* Thumbhash.swift in Sources */,
+				FEC340D32E7326630050078A /* Request.swift in Sources */,
+				FEC340D42E7326630050078A /* ThumbnailResolver.swift in Sources */,
+				FEC340D52E7326630050078A /* Thumbnails.g.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

mobile/ios/Runner/AppDelegate.swift

@@ -15,7 +15,7 @@ import UIKit
   ) -> Bool {
     // Required for flutter_local_notification
     if #available(iOS 10.0, *) {
-      UNUserNotificationCenter.current().delegate = self as? UNUserNotificationCenterDelegate
+      UNUserNotificationCenter.current().delegate = self as UNUserNotificationCenterDelegate
     }
 
     GeneratedPluginRegistrant.register(with: self)
@@ -53,7 +53,7 @@ import UIKit
   
   public static func registerPlugins(binaryMessenger: FlutterBinaryMessenger) {
     NativeSyncApiSetup.setUp(binaryMessenger: binaryMessenger, api: NativeSyncApiImpl())
-    ThumbnailApiSetup.setUp(binaryMessenger: binaryMessenger, api: ThumbnailApiImpl())
+    ThumbnailApiSetup.setUp(binaryMessenger: binaryMessenger, api: ThumbnailResolver())
     BackgroundWorkerFgHostApiSetup.setUp(binaryMessenger: binaryMessenger, api: BackgroundWorkerApiImpl())
   }
 }

mobile/ios/Runner/Images/ThumbnailsImpl.swift

@@ -1,211 +0,0 @@
-import CryptoKit
-import Flutter
-import MobileCoreServices
-import Photos
-
-class Request {
-  weak var workItem: DispatchWorkItem?
-  var isCancelled = false
-  let callback: (Result<[String: Int64], any Error>) -> Void
-  
-  init(callback: @escaping (Result<[String: Int64], any Error>) -> Void) {
-    self.callback = callback
-  }
-}
-
-class ThumbnailApiImpl: ThumbnailApi {
-  private static let imageManager = PHImageManager.default()
-  private static let fetchOptions = {
-    let fetchOptions = PHFetchOptions()
-    fetchOptions.fetchLimit = 1
-    fetchOptions.wantsIncrementalChangeDetails = false
-    return fetchOptions
-  }()
-  private static let requestOptions = {
-    let requestOptions = PHImageRequestOptions()
-    requestOptions.isNetworkAccessAllowed = true
-    requestOptions.deliveryMode = .highQualityFormat
-    requestOptions.resizeMode = .fast
-    requestOptions.isSynchronous = true
-    requestOptions.version = .current
-    return requestOptions
-  }()
-  
-  private static let assetQueue = DispatchQueue(label: "thumbnail.assets", qos: .userInitiated)
-  private static let requestQueue = DispatchQueue(label: "thumbnail.requests", qos: .userInitiated)
-  private static let cancelQueue = DispatchQueue(label: "thumbnail.cancellation", qos: .default)
-  private static let processingQueue = DispatchQueue(label: "thumbnail.processing", qos: .userInteractive, attributes: .concurrent)
-  
-  private static let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
-  private static let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue).rawValue
-  private static var requests = [Int64: Request]()
-  private static let cancelledResult = Result<[String: Int64], any Error>.success([:])
-  private static let concurrencySemaphore = DispatchSemaphore(value: ProcessInfo.processInfo.activeProcessorCount * 2)
-  private static let assetCache = {
-    let assetCache = NSCache<NSString, PHAsset>()
-    assetCache.countLimit = 10000
-    return assetCache
-  }()
-  private static let activitySemaphore = DispatchSemaphore(value: 1)
-  private static let willResignActiveObserver = NotificationCenter.default.addObserver(
-    forName: UIApplication.willResignActiveNotification,
-    object: nil,
-    queue: .main
-  ) { _ in
-    processingQueue.suspend()
-    activitySemaphore.wait()
-  }
-  private static let didBecomeActiveObserver = NotificationCenter.default.addObserver(
-    forName: UIApplication.didBecomeActiveNotification,
-    object: nil,
-    queue: .main
-  ) { _ in
-    processingQueue.resume()
-    activitySemaphore.signal()
-  }
-  
-  func getThumbhash(thumbhash: String, completion: @escaping (Result<[String : Int64], any Error>) -> Void) {
-    Self.processingQueue.async {
-      guard let data = Data(base64Encoded: thumbhash)
-      else { return completion(.failure(PigeonError(code: "", message: "Invalid base64 string: \(thumbhash)", details: nil)))}
-
-      let (width, height, pointer) = thumbHashToRGBA(hash: data)
-      self.waitForActiveState()
-      completion(.success(["pointer": Int64(Int(bitPattern: pointer.baseAddress)), "width": Int64(width), "height": Int64(height)]))
-    }
-  }
-  
-  func requestImage(assetId: String, requestId: Int64, width: Int64, height: Int64, isVideo: Bool, completion: @escaping (Result<[String: Int64], any Error>) -> Void) {
-    let request = Request(callback: completion)
-    let item = DispatchWorkItem {
-      if request.isCancelled {
-        return completion(Self.cancelledResult)
-      }
-      
-      Self.concurrencySemaphore.wait()
-      defer {
-        Self.concurrencySemaphore.signal()
-      }
-      
-      if request.isCancelled {
-        return completion(Self.cancelledResult)
-      }
-      
-      guard let asset = Self.requestAsset(assetId: assetId)
-      else {
-        Self.removeRequest(requestId: requestId)
-        completion(.failure(PigeonError(code: "", message: "Could not get asset data for \(assetId)", details: nil)))
-        return
-      }
-      
-      if request.isCancelled {
-        return completion(Self.cancelledResult)
-      }
-      
-      var image: UIImage?
-      Self.imageManager.requestImage(
-        for: asset,
-        targetSize: width > 0 && height > 0 ? CGSize(width: Double(width), height: Double(height)) : PHImageManagerMaximumSize,
-        contentMode: .aspectFill,
-        options: Self.requestOptions,
-        resultHandler: { (_image, info) -> Void in
-          image = _image
-        }
-      )
-      
-      if request.isCancelled {
-        return completion(Self.cancelledResult)
-      }
-      
-      guard let image = image,
-            let cgImage = image.cgImage else {
-        Self.removeRequest(requestId: requestId)
-        return completion(.failure(PigeonError(code: "", message: "Could not get pixel data for \(assetId)", details: nil)))
-      }
-      
-      let pointer = UnsafeMutableRawPointer.allocate(
-        byteCount: Int(cgImage.width) * Int(cgImage.height) * 4,
-        alignment: MemoryLayout<UInt8>.alignment
-      )
-      
-      if request.isCancelled {
-        pointer.deallocate()
-        return completion(Self.cancelledResult)
-      }
-      
-      guard let context = CGContext(
-        data: pointer,
-        width: cgImage.width,
-        height: cgImage.height,
-        bitsPerComponent: 8,
-        bytesPerRow: cgImage.width * 4,
-        space: Self.rgbColorSpace,
-        bitmapInfo: Self.bitmapInfo
-      ) else {
-        pointer.deallocate()
-        Self.removeRequest(requestId: requestId)
-        return completion(.failure(PigeonError(code: "", message: "Could not create context for \(assetId)", details: nil)))
-      }
-      
-      if request.isCancelled {
-        pointer.deallocate()
-        return completion(Self.cancelledResult)
-      }
-      
-      context.interpolationQuality = .none
-      context.draw(cgImage, in: CGRect(x: 0, y: 0, width: cgImage.width, height: cgImage.height))
-      
-      if request.isCancelled {
-        pointer.deallocate()
-        return completion(Self.cancelledResult)
-      }
-      
-      self.waitForActiveState()
-      completion(.success(["pointer": Int64(Int(bitPattern: pointer)), "width": Int64(cgImage.width), "height": Int64(cgImage.height)]))
-      Self.removeRequest(requestId: requestId)
-    }
-    
-    request.workItem = item
-    Self.addRequest(requestId: requestId, request: request)
-    Self.processingQueue.async(execute: item)
-  }
-  
-  func cancelImageRequest(requestId: Int64) {
-    Self.cancelRequest(requestId: requestId)
-  }
-  
-  private static func addRequest(requestId: Int64, request: Request) -> Void {
-    requestQueue.sync { requests[requestId] = request }
-  }
-  
-  private static func removeRequest(requestId: Int64) -> Void {
-    requestQueue.sync { requests[requestId] = nil }
-  }
-  
-  private static func cancelRequest(requestId: Int64) -> Void {
-    requestQueue.async {
-      guard let request = requests.removeValue(forKey: requestId) else { return }
-      request.isCancelled = true
-      guard let item = request.workItem else { return }
-      if item.isCancelled {
-        cancelQueue.async { request.callback(Self.cancelledResult) }
-      }
-    }
-  }
-  
-  private static func requestAsset(assetId: String) -> PHAsset? {
-    var asset: PHAsset?
-    assetQueue.sync { asset = assetCache.object(forKey: assetId as NSString) }
-    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) }
-    return asset
-  }
-  
-  func waitForActiveState() {
-    Self.activitySemaphore.wait()
-    Self.activitySemaphore.signal()
-  }
-}

mobile/ios/Runner/Resolvers/Assets/AssetResolver.swift

@@ -0,0 +1,115 @@
+import Photos
+
+class AssetRequest: Request {
+  let assetId: String
+  var completion: (PHAsset?) -> Void
+  
+  init(cancellationToken: CancellationToken, assetId: String, completion: @escaping (PHAsset?) -> Void) {
+    self.assetId = assetId
+    self.completion = completion
+    super.init(cancellationToken: cancellationToken)
+  }
+}
+
+class AssetResolver {
+  private let requestQueue: DispatchQueue
+  private let processingQueue: DispatchQueue
+  
+  private var batchTimer: DispatchWorkItem?
+  private let batchLock = NSLock()
+  private let batchTimeout: TimeInterval
+  
+  private let fetchOptions: PHFetchOptions
+  private var assetRequests = [AssetRequest]()
+  private let assetCache: NSCache<NSString, PHAsset>
+  
+  init(
+    fetchOptions: PHFetchOptions,
+    batchTimeout: TimeInterval = 0.00025, // 250μs
+    cacheSize: Int = 10000,
+    qos: DispatchQoS = .unspecified
+  ) {
+    self.fetchOptions = fetchOptions
+    self.batchTimeout = batchTimeout
+    self.assetCache =  NSCache<NSString, PHAsset>()
+    self.assetCache.countLimit = cacheSize
+    self.requestQueue = DispatchQueue(label: "assets.requests", qos: qos)
+    self.processingQueue = DispatchQueue(label: "assets.processing", qos: qos)
+  }
+  
+  func requestAsset(request: AssetRequest) {
+    requestQueue.async {
+      if (request.isCancelled) {
+        request.completion(nil)
+        return
+      }
+      
+      if let cachedAsset = self.assetCache.object(forKey: request.assetId as NSString) {
+        request.completion(cachedAsset)
+        return
+      }
+      
+      self.batchLock.lock()
+      if (request.isCancelled) {
+        self.batchLock.unlock()
+        request.completion(nil)
+        return
+      }
+      
+      self.assetRequests.append(request)
+      
+      self.batchTimer?.cancel()
+      let timer = DispatchWorkItem(block: self.processBatch)
+      self.batchTimer = timer
+      self.batchLock.unlock()
+      self.processingQueue.asyncAfter(deadline: .now() + self.batchTimeout, execute: timer)
+    }
+  }
+  
+  private func processBatch() {
+    batchLock.lock()
+    if assetRequests.isEmpty {
+      batchTimer = nil
+      batchLock.unlock()
+      return
+    }
+    
+    var completionMap = [String: [(PHAsset?) -> Void]]()
+    var activeAssetIds = [String]()
+    completionMap.reserveCapacity(assetRequests.count)
+    activeAssetIds.reserveCapacity(assetRequests.count)
+    for request in assetRequests {
+      if (request.isCancelled) {
+        request.completion(nil)
+        continue
+      }
+      
+      if var completions = completionMap[request.assetId] {
+        completions.append(request.completion)
+      } else {
+        activeAssetIds.append(request.assetId)
+        completionMap[request.assetId] = [request.completion]
+      }
+    }
+    assetRequests.removeAll(keepingCapacity: true)
+    batchTimer = nil
+    batchLock.unlock()
+    
+    guard !activeAssetIds.isEmpty else { return }
+    
+    let assets = PHAsset.fetchAssets(withLocalIdentifiers: activeAssetIds, options: self.fetchOptions)
+    assets.enumerateObjects { asset, _, _ in
+      let assetId = asset.localIdentifier
+      for completion in completionMap.removeValue(forKey: assetId)! {
+        completion(asset)
+      }
+      self.requestQueue.async { self.assetCache.setObject(asset, forKey: assetId as NSString) }
+    }
+    
+    for completions in completionMap.values {
+      for completion in completions {
+        completion(nil)
+      }
+    }
+  }
+}

mobile/ios/Runner/Resolvers/Images/ThumbnailResolver.swift

@@ -0,0 +1,198 @@
+import CryptoKit
+import Flutter
+import MobileCoreServices
+import Photos
+
+class ThumbnailRequest: Request {
+  weak var workItem: DispatchWorkItem?
+  let completion: (Result<[String: Int64], any Error>) -> Void
+  
+  init(cancellationToken: CancellationToken, completion: @escaping (Result<[String: Int64], any Error>) -> Void) {
+    self.completion = completion
+    super.init(cancellationToken: cancellationToken)
+  }
+}
+
+class ThumbnailResolver: ThumbnailApi {
+  private static let imageManager = PHImageManager.default()
+  private static let assetResolver = AssetResolver(fetchOptions: {
+    let fetchOptions = PHFetchOptions()
+    fetchOptions.wantsIncrementalChangeDetails = false
+    return fetchOptions
+  }(), qos: .userInitiated)
+  private static let requestOptions = {
+    let requestOptions = PHImageRequestOptions()
+    requestOptions.isNetworkAccessAllowed = true
+    requestOptions.deliveryMode = .highQualityFormat
+    requestOptions.resizeMode = .fast
+    requestOptions.isSynchronous = true
+    requestOptions.version = .current
+    return requestOptions
+  }()
+  
+  private static let requestQueue = DispatchQueue(label: "thumbnail.requests", qos: .userInitiated)
+  private static let cancelQueue = DispatchQueue(label: "thumbnail.cancellation", qos: .default)
+  private static let processingQueue = DispatchQueue(label: "thumbnail.processing", qos: .userInteractive, attributes: .concurrent)
+  
+  private static let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
+  private static let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue).rawValue
+  private static var requests = [Int64: ThumbnailRequest]()
+  private static let cancelledResult = Result<[String: Int64], any Error>.success([:])
+  private static let thumbnailConcurrencySemaphore = DispatchSemaphore(value: ProcessInfo.processInfo.activeProcessorCount / 2 + 1)
+  private static let activitySemaphore = DispatchSemaphore(value: 1)
+  
+  private static let willResignActiveObserver = NotificationCenter.default.addObserver(
+    forName: UIApplication.willResignActiveNotification,
+    object: nil,
+    queue: .main
+  ) { _ in
+    processingQueue.suspend()
+    activitySemaphore.wait()
+  }
+  private static let didBecomeActiveObserver = NotificationCenter.default.addObserver(
+    forName: UIApplication.didBecomeActiveNotification,
+    object: nil,
+    queue: .main
+  ) { _ in
+    processingQueue.resume()
+    activitySemaphore.signal()
+  }
+  
+  func getThumbhash(thumbhash: String, completion: @escaping (Result<[String : Int64], any Error>) -> Void) {
+    Self.processingQueue.async {
+      guard let data = Data(base64Encoded: thumbhash)
+      else { return completion(.failure(PigeonError(code: "", message: "Invalid base64 string: \(thumbhash)", details: nil)))}
+      
+      let (width, height, pointer) = thumbHashToRGBA(hash: data)
+      self.waitForActiveState()
+      completion(.success(["pointer": Int64(Int(bitPattern: pointer.baseAddress)), "width": Int64(width), "height": Int64(height)]))
+    }
+  }
+  
+  func requestImage(assetId: String, requestId: Int64, width: Int64, height: Int64, isVideo: Bool, completion: @escaping (Result<[String: Int64], any Error>) -> Void) {
+    let cancellationToken = CancellationToken()
+    let thumbnailRequest = ThumbnailRequest(cancellationToken: cancellationToken, completion: completion)
+    Self.assetResolver.requestAsset(request: AssetRequest(cancellationToken: cancellationToken, assetId: assetId) { asset in
+      if cancellationToken.isCancelled {
+        return completion(Self.cancelledResult)
+      }
+      
+      let item = DispatchWorkItem {
+        if cancellationToken.isCancelled {
+          return completion(Self.cancelledResult)
+        }
+        
+        guard let asset = asset else {
+          if cancellationToken.isCancelled {
+            return completion(Self.cancelledResult)
+          }
+          Self.removeRequest(requestId: requestId)
+          completion(.failure(PigeonError(code: "", message: "Could not get asset data for \(assetId)", details: nil)))
+          return
+        }
+        
+        Self.thumbnailConcurrencySemaphore.wait()
+        defer { Self.thumbnailConcurrencySemaphore.signal() }
+        
+        if cancellationToken.isCancelled {
+          return completion(Self.cancelledResult)
+        }
+        
+        var image: UIImage?
+        Self.imageManager.requestImage(
+          for: asset,
+          targetSize: width > 0 && height > 0 ? CGSize(width: Double(width), height: Double(height)) : PHImageManagerMaximumSize,
+          contentMode: .aspectFill,
+          options: Self.requestOptions,
+          resultHandler: { (_image, info) -> Void in
+            image = _image
+          }
+        )
+        
+        if cancellationToken.isCancelled {
+          return completion(Self.cancelledResult)
+        }
+        
+        guard let image = image,
+              let cgImage = image.cgImage else {
+          Self.removeRequest(requestId: requestId)
+          return completion(.failure(PigeonError(code: "", message: "Could not get pixel data for \(assetId)", details: nil)))
+        }
+        
+        let pointer = UnsafeMutableRawPointer.allocate(
+          byteCount: Int(cgImage.width) * Int(cgImage.height) * 4,
+          alignment: MemoryLayout<UInt8>.alignment
+        )
+        
+        if cancellationToken.isCancelled {
+          pointer.deallocate()
+          return completion(Self.cancelledResult)
+        }
+        
+        guard let context = CGContext(
+          data: pointer,
+          width: cgImage.width,
+          height: cgImage.height,
+          bitsPerComponent: 8,
+          bytesPerRow: cgImage.width * 4,
+          space: Self.rgbColorSpace,
+          bitmapInfo: Self.bitmapInfo
+        ) else {
+          pointer.deallocate()
+          Self.removeRequest(requestId: requestId)
+          return completion(.failure(PigeonError(code: "", message: "Could not create context for \(assetId)", details: nil)))
+        }
+        
+        if cancellationToken.isCancelled {
+          pointer.deallocate()
+          return completion(Self.cancelledResult)
+        }
+        
+        context.interpolationQuality = .none
+        context.draw(cgImage, in: CGRect(x: 0, y: 0, width: cgImage.width, height: cgImage.height))
+        
+        if cancellationToken.isCancelled {
+          pointer.deallocate()
+          return completion(Self.cancelledResult)
+        }
+        
+        self.waitForActiveState()
+        completion(.success(["pointer": Int64(Int(bitPattern: pointer)), "width": Int64(cgImage.width), "height": Int64(cgImage.height)]))
+        Self.removeRequest(requestId: requestId)
+      }
+      thumbnailRequest.workItem = item
+      Self.processingQueue.async(execute: item)
+    })
+    
+    Self.addRequest(requestId: requestId, request: thumbnailRequest)
+  }
+  
+  func cancelImageRequest(requestId: Int64) {
+    Self.cancelRequest(requestId: requestId)
+  }
+  
+  private static func addRequest(requestId: Int64, request: ThumbnailRequest) -> Void {
+    requestQueue.sync { requests[requestId] = request }
+  }
+  
+  private static func removeRequest(requestId: Int64) -> Void {
+    requestQueue.sync { requests[requestId] = nil }
+  }
+  
+  private static func cancelRequest(requestId: Int64) -> Void {
+    requestQueue.async {
+      guard let request = requests.removeValue(forKey: requestId) else { return }
+      request.isCancelled = true
+      guard let item = request.workItem else { return }
+      item.cancel()
+      if item.isCancelled {
+        cancelQueue.async { request.completion(Self.cancelledResult) }
+      }
+    }
+  }
+  
+  func waitForActiveState() {
+    Self.activitySemaphore.wait()
+    Self.activitySemaphore.signal()
+  }
+}

mobile/ios/Runner/Resolvers/Request.swift

@@ -0,0 +1,20 @@
+class CancellationToken {
+  var isCancelled = false
+}
+
+class Request {
+  let cancellationToken: CancellationToken
+
+  init(cancellationToken: CancellationToken) {
+    self.cancellationToken = cancellationToken
+  }
+  
+  var isCancelled: Bool {
+    get {
+      return cancellationToken.isCancelled
+    }
+    set(newValue) {
+      cancellationToken.isCancelled = newValue
+    }
+  }
+}