improve concurrency

mobile/ios/Runner/Images/ImageProcessing.swift

@@ -0,0 +1,7 @@
+import Foundation
+
+enum ImageProcessing {
+  static let queue = DispatchQueue(label: "thumbnail.processing", qos: .userInitiated, attributes: .concurrent)
+  static let semaphore = DispatchSemaphore(value: ProcessInfo.processInfo.activeProcessorCount * 2)
+  static let cancelledResult = Result<[String: Int64]?, any Error>.success(nil)
+}

mobile/ios/Runner/Images/LocalImagesImpl.swift

@@ -34,7 +34,6 @@ class LocalImageApiImpl: LocalImageApi {
   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 var rgbaFormat = vImage_CGImageFormat(
     bitsPerComponent: 8,
@@ -44,8 +43,6 @@ class LocalImageApiImpl: LocalImageApi {
     renderingIntent: .defaultIntent
   )!
   private static var requests = [Int64: LocalImageRequest]()
-  private static let cancelledResult = Result<[String: Int64]?, any Error>.success(nil)
-  private static let concurrencySemaphore = DispatchSemaphore(value: ProcessInfo.processInfo.activeProcessorCount * 2)
   private static let assetCache = {
     let assetCache = NSCache<NSString, PHAsset>()
     assetCache.countLimit = 10000
@@ -53,7 +50,7 @@ class LocalImageApiImpl: LocalImageApi {
   }()
   
   func getThumbhash(thumbhash: String, completion: @escaping (Result<[String : Int64], any Error>) -> Void) {
-    Self.processingQueue.async {
+    ImageProcessing.queue.async {
       guard let data = Data(base64Encoded: thumbhash)
       else { return completion(.failure(PigeonError(code: "", message: "Invalid base64 string: \(thumbhash)", details: nil)))}
       
@@ -71,16 +68,16 @@ class LocalImageApiImpl: LocalImageApi {
     let request = LocalImageRequest(callback: completion)
     let item = DispatchWorkItem {
       if request.isCancelled {
-        return completion(Self.cancelledResult)
+        return completion(ImageProcessing.cancelledResult)
       }
       
-      Self.concurrencySemaphore.wait()
+      ImageProcessing.semaphore.wait()
       defer {
-        Self.concurrencySemaphore.signal()
+        ImageProcessing.semaphore.signal()
       }
       
       if request.isCancelled {
-        return completion(Self.cancelledResult)
+        return completion(ImageProcessing.cancelledResult)
       }
       
       guard let asset = Self.requestAsset(assetId: assetId)
@@ -91,7 +88,7 @@ class LocalImageApiImpl: LocalImageApi {
       }
       
       if request.isCancelled {
-        return completion(Self.cancelledResult)
+        return completion(ImageProcessing.cancelledResult)
       }
       
       var image: UIImage?
@@ -116,7 +113,7 @@ class LocalImageApiImpl: LocalImageApi {
       }
       
       if request.isCancelled {
-        return completion(Self.cancelledResult)
+        return completion(ImageProcessing.cancelledResult)
       }
       
       do {
@@ -124,7 +121,7 @@ class LocalImageApiImpl: LocalImageApi {
         
         if request.isCancelled {
           buffer.free()
-          return completion(Self.cancelledResult)
+          return completion(ImageProcessing.cancelledResult)
         }
         
         request.callback(.success([
@@ -143,7 +140,7 @@ class LocalImageApiImpl: LocalImageApi {
     
     request.workItem = item
     Self.add(requestId: requestId, request: request)
-    Self.processingQueue.async(execute: item)
+    ImageProcessing.queue.async(execute: item)
   }
   
   func cancelRequest(requestId: Int64) {
@@ -164,7 +161,7 @@ class LocalImageApiImpl: LocalImageApi {
       request.isCancelled = true
       guard let item = request.workItem else { return }
       if item.isCancelled {
-        cancelQueue.async { request.callback(Self.cancelledResult) }
+        cancelQueue.async { request.callback(ImageProcessing.cancelledResult) }
       }
     }
   }

mobile/ios/Runner/Images/RemoteImagesImpl.swift

@@ -19,7 +19,6 @@ class RemoteImageRequest {
 class RemoteImageApiImpl: NSObject, RemoteImageApi {
   private static var lock = os_unfair_lock()
   private static var requests = [Int64: RemoteImageRequest]()
-  private static let cancelledResult = Result<[String: Int64]?, any Error>.success(nil)
   private static var rgbaFormat = vImage_CGImageFormat(
     bitsPerComponent: 8,
     bitsPerPixel: 32,
@@ -64,45 +63,54 @@ class RemoteImageApiImpl: NSObject, RemoteImageApi {
 
     if let error = error {
       if request.isCancelled || (error as NSError).code == NSURLErrorCancelled {
-        return request.completion(cancelledResult)
+        return request.completion(ImageProcessing.cancelledResult)
       }
       return request.completion(.failure(error))
     }
 
     if request.isCancelled {
-      return request.completion(cancelledResult)
+      return request.completion(ImageProcessing.cancelledResult)
     }
 
     guard let data = data else {
       return request.completion(.failure(PigeonError(code: "", message: "No data received", details: nil)))
     }
 
-    guard let imageSource = CGImageSourceCreateWithData(data as CFData, nil),
-          let cgImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, decodeOptions) else {
-      return request.completion(.failure(PigeonError(code: "", message: "Failed to decode image for request", details: nil)))
-    }
-
-    if request.isCancelled {
-      return request.completion(cancelledResult)
-    }
-
-    do {
-      let buffer = try vImage_Buffer(cgImage: cgImage, format: rgbaFormat)
+    ImageProcessing.queue.async {
+      ImageProcessing.semaphore.wait()
+      defer { ImageProcessing.semaphore.signal() }
 
       if request.isCancelled {
-        buffer.free()
-        return request.completion(cancelledResult)
+        return request.completion(ImageProcessing.cancelledResult)
       }
 
-      request.completion(
-        .success([
-          "pointer": Int64(Int(bitPattern: buffer.data)),
-          "width": Int64(buffer.width),
-          "height": Int64(buffer.height),
-          "rowBytes": Int64(buffer.rowBytes),
-        ]))
-    } catch {
-      return request.completion(.failure(PigeonError(code: "", message: "Failed to convert image for request: \(error)", details: nil)))
+      guard let imageSource = CGImageSourceCreateWithData(data as CFData, nil),
+            let cgImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, decodeOptions) else {
+        return request.completion(.failure(PigeonError(code: "", message: "Failed to decode image for request", details: nil)))
+      }
+
+      if request.isCancelled {
+        return request.completion(ImageProcessing.cancelledResult)
+      }
+
+      do {
+        let buffer = try vImage_Buffer(cgImage: cgImage, format: rgbaFormat)
+
+        if request.isCancelled {
+          buffer.free()
+          return request.completion(ImageProcessing.cancelledResult)
+        }
+
+        request.completion(
+          .success([
+            "pointer": Int64(Int(bitPattern: buffer.data)),
+            "width": Int64(buffer.width),
+            "height": Int64(buffer.height),
+            "rowBytes": Int64(buffer.rowBytes),
+          ]))
+      } catch {
+        return request.completion(.failure(PigeonError(code: "", message: "Failed to convert image for request: \(error)", details: nil)))
+      }
     }
   }