PluginMediaStreamRenderer.mediaStreamChanged() has multithreading race condition

[RSATom]

over PluginMediaStream.videoTracks

The problem is PluginMediaStreamRenderer.mediaStreamChanged() uses pluginMediaStream.videoTracks from main thread while iosrtcPlugin.MediaStream_removeTrack can remove tracks from thread owned by iosrtcPlugin.queue...

[hthetiot]

Poposed fix add new DispatchQueue for tracks set/get and serialization alternative is to use same iosrtcPlugin.queue may be.

--- src/PluginMediaStream.swift (original)
+++ src/PluginMediaStream.swift (thread-safe with consistent setters)
@@ -5,8 +5,23 @@ class PluginMediaStream : NSObject {
 
 	var rtcMediaStream: RTCMediaStream
 	var id: String
-	var audioTracks: [String : PluginMediaStreamTrack] = [:]
-	var videoTracks: [String : PluginMediaStreamTrack] = [:]
+	private var _audioTracks: [String : PluginMediaStreamTrack] = [:]
+	private var _videoTracks: [String : PluginMediaStreamTrack] = [:]
+	private let tracksQueue = DispatchQueue(label: "PluginMediaStream.tracks", attributes: .concurrent)
+	
 	var eventListener: ((_ data: NSDictionary) -> Void)?
 	var eventListenerForAddTrack: ((_ pluginMediaStreamTrack: PluginMediaStreamTrack) -> Void)?
 	var eventListenerForRemoveTrack: ((_ pluginMediaStreamTrack: PluginMediaStreamTrack) -> Void)?
+
+	// Thread-safe accessors with sync barrier writes
+	var audioTracks: [String : PluginMediaStreamTrack] {
+		get {
+			return tracksQueue.sync { _audioTracks }
+		}
+		set {
+			tracksQueue.sync(flags: .barrier) { _audioTracks = newValue }
+		}
+	}
+	
+	var videoTracks: [String : PluginMediaStreamTrack] {
+		get {
+			return tracksQueue.sync { _videoTracks }
+		}
+		set {
+			tracksQueue.sync(flags: .barrier) { _videoTracks = newValue }
+		}
+	}
 
 	/**
 	 * Constructor for pc.onaddstream event and getUserMedia().
@@ -25,6 +40,8 @@ class PluginMediaStream : NSObject {
 		} else {
 			self.id = streamId!;
 		}
+
+		super.init()
 
 		for track: RTCMediaStreamTrack in (self.rtcMediaStream.audioTracks as Array<RTCMediaStreamTrack>) {
 			let pluginMediaStreamTrack = PluginMediaStreamTrack(rtcMediaStreamTrack: track)
@@ -57,12 +74,22 @@ class PluginMediaStream : NSObject {
 	}
 
 	func getJSON() -> NSDictionary {
-		let json: NSMutableDictionary = [
-			"id": self.id,
-			"audioTracks": NSMutableDictionary(),
-			"videoTracks": NSMutableDictionary()
-		]
+		return tracksQueue.sync {
+			let json: NSMutableDictionary = [
+				"id": self.id,
+				"audioTracks": NSMutableDictionary(),
+				"videoTracks": NSMutableDictionary()
+			]
+
+			for (id, pluginMediaStreamTrack) in self._audioTracks {
+				(json["audioTracks"] as! NSMutableDictionary)[id] = pluginMediaStreamTrack.getJSON()
+			}
 
-		for (id, pluginMediaStreamTrack) in self.audioTracks {
-			(json["audioTracks"] as! NSMutableDictionary)[id] = pluginMediaStreamTrack.getJSON()
-		}
+			for (id, pluginMediaStreamTrack) in self._videoTracks {
+				(json["videoTracks"] as! NSMutableDictionary)[id] = pluginMediaStreamTrack.getJSON()
+			}
 
-		for (id, pluginMediaStreamTrack) in self.videoTracks {
-			(json["videoTracks"] as! NSMutableDictionary)[id] = pluginMediaStreamTrack.getJSON()
+			return json as NSDictionary
 		}
-
-		return json as NSDictionary
 	}
 
 	func setListener(
@@ -82,9 +109,13 @@ class PluginMediaStream : NSObject {
 	}
 
 	func hasTrack(_ pluginMediaStreamTrack: PluginMediaStreamTrack) -> Bool {
-		if pluginMediaStreamTrack.kind == "audio" {
-			return self.audioTracks[pluginMediaStreamTrack.id] != nil;
-		} else if pluginMediaStreamTrack.kind == "video" {
-			return self.videoTracks[pluginMediaStreamTrack.id] != nil;
-		} else {
-			return false
+		return tracksQueue.sync {
+			if pluginMediaStreamTrack.kind == "audio" {
+				return self._audioTracks[pluginMediaStreamTrack.id] != nil;
+			} else if pluginMediaStreamTrack.kind == "video" {
+				return self._videoTracks[pluginMediaStreamTrack.id] != nil;
+			} else {
+				return false
+			}
 		}
 	}

[RSATom]

@hthetiot sorry, I don't use iosrtc anymore, and can't check your solution 😞