Do not leak Sendable extensions to consumers (#848)

LiveKit currently marks multiple types that are not thread-safe as being
`Sendable`. These extensions mean that consumer's applications also
treat these types as `Sendable`, which can lead to thread-safety bugs.

This PR removes the Sendable extensions without adding new warnings.
This is accomplished by utilizing internal wrapper types that are marked
as `@unchecked Sendable`.

---------

Co-authored-by: Błażej Pankowski <[email protected]>

Author: dfed

.changes/sendable-extension

@@ -0,0 +1 @@
+patch type="changed" "Removed '@unchecked Sendable' extensions on common types"

Sources/LiveKit/Extensions/Sendable.swift

@@ -48,8 +48,6 @@ extension LKRTCCallbackLogger: @unchecked Swift.Sendable {}
 
 // MARK: Collections
 
-extension NSHashTable: @unchecked Swift.Sendable {} // cannot specify Obj-C generics
-extension NSMapTable: @unchecked Swift.Sendable {} // cannot specify Obj-C generics
 #if swift(<6.2)
 extension Dictionary: Swift.Sendable where Key: Sendable, Value: Sendable {}
 #endif
@@ -58,4 +56,3 @@ extension Dictionary: Swift.Sendable where Key: Sendable, Value: Sendable {}
 
 extension AVCaptureDevice: @unchecked Swift.Sendable {}
 extension AVCaptureDevice.Format: @unchecked Swift.Sendable {}
-extension CVPixelBuffer: @unchecked Swift.Sendable {}

Sources/LiveKit/Support/MapTable.swift

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2025 LiveKit
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import Foundation
+
+/// A thin unchecked sendable wrapper around NSMapTable.
+final class MapTable<KeyType, ObjectType>: @unchecked Sendable where KeyType: AnyObject, ObjectType: AnyObject {
+    init(_ mapTable: NSMapTable<KeyType, ObjectType>) {
+        self.mapTable = mapTable
+    }
+
+    class func weakToStrongObjects() -> MapTable<KeyType, ObjectType> {
+        .init(.weakToStrongObjects())
+    }
+
+    func object(forKey aKey: KeyType?) -> ObjectType? {
+        mapTable.object(forKey: aKey)
+    }
+
+    func removeObject(forKey aKey: KeyType?) {
+        mapTable.removeObject(forKey: aKey)
+    }
+
+    func setObject(_ anObject: ObjectType?, forKey aKey: KeyType?) {
+        mapTable.setObject(anObject, forKey: aKey)
+    }
+
+    var count: Int {
+        mapTable.count
+    }
+
+    func objectEnumerator() -> NSEnumerator? {
+        mapTable.objectEnumerator()
+    }
+
+    func removeAllObjects() {
+        mapTable.removeAllObjects()
+    }
+
+    private let mapTable: NSMapTable<KeyType, ObjectType>
+}

Sources/LiveKit/Track/Track.swift

@@ -128,7 +128,7 @@ public class Track: NSObject, @unchecked Sendable, Loggable {
         var rtpReceiver: LKRTCRtpReceiver?
 
         // All VideoRendererAdapters attached to this track, key/value for direct removal.
-        var videoRendererAdapters = NSMapTable<VideoRenderer, VideoRendererAdapter>.weakToStrongObjects()
+        var videoRendererAdapters = MapTable<VideoRenderer, VideoRendererAdapter>.weakToStrongObjects()
     }
 
     let _state: StateSync<State>

Sources/LiveKit/Types/Options/CameraCaptureOptions.swift

@@ -25,7 +25,7 @@ public final class CameraCaptureOptions: NSObject, VideoCaptureOptions, Sendable
     public let deviceType: AVCaptureDevice.DeviceType?
     #endif
 
-    /// Exact devce to use.
+    /// Exact device to use.
     @objc
     public let device: AVCaptureDevice?
 

Sources/LiveKit/VideoProcessors/BackgroundBlurVideoProcessor.swift

@@ -133,14 +133,18 @@ public final class BackgroundBlurVideoProcessor: NSObject, @unchecked Sendable,
     private func cacheMask(inputBuffer: CVPixelBuffer, inputDimensions: CGSize) {
         guard frameCount % segmentationFrameInterval == 0 else { return }
 
+        struct PixelBufferHolder: @unchecked Sendable {
+            let buffer: CVPixelBuffer
+        }
+        let inputBuffer = PixelBufferHolder(buffer: inputBuffer)
         segmentationQueue.async {
             #if LK_SIGNPOSTS
             os_signpost(.begin, log: self.signpostLog, name: #function)
             defer {
                 os_signpost(.end, log: self.signpostLog, name: #function)
             }
             #endif
-            try? self.segmentationRequestHandler.perform([self.segmentationRequest], on: inputBuffer)
+            try? self.segmentationRequestHandler.perform([self.segmentationRequest], on: inputBuffer.buffer)
 
             guard let maskPixelBuffer = self.segmentationRequest.results?.first?.pixelBuffer else { return }
             let maskImage = CIImage(cvPixelBuffer: maskPixelBuffer)