Fix race condition with videoTrack.addRenderer (#448)

@@ -52,6 +52,16 @@ abstract class Track(
     var statsGetter: RTCStatsGetter? = null
     var statsGetter: RTCStatsGetter? = null
 
 
     /**
     /**
+     * [MediaStreamTrack] doesn't expose a way to tell if it's disposed. Track it here.
+     * This can only be safely accessed on the rtc thread.
+     *
+     * Note: [MediaStreamTrack] can still be disposed if we don't own it, so this isn't necessarily safe,
+     * however generally all the tracks passed into this class are owned by this class.
+     */
+    internal var isDisposed = false
+        private set
+
+    /**
      * Return the [RTCStatsReport] for this track, or null if none is available.
      * Return the [RTCStatsReport] for this track, or null if none is available.
      */
      */
     suspend fun getRTCStats(): RTCStatsReport? = statsGetter?.getStats()
     suspend fun getRTCStats(): RTCStatsReport? = statsGetter?.getStats()
@@ -172,6 +182,7 @@ abstract class Track(
      */
      */
     open fun dispose() {
     open fun dispose() {
         executeBlockingOnRTCThread {
         executeBlockingOnRTCThread {
+            isDisposed = true
             rtcTrack.dispose()
             rtcTrack.dispose()
         }
         }
     }
     }

@@ -35,26 +35,32 @@ abstract class VideoTrack(name: String, override val rtcTrack: VideoTrack) :
      */
      */
     open fun addRenderer(renderer: VideoSink) {
     open fun addRenderer(renderer: VideoSink) {
         executeBlockingOnRTCThread {
         executeBlockingOnRTCThread {
+            if (!isDisposed) {
                 sinks.add(renderer)
                 sinks.add(renderer)
                 rtcTrack.addSink(renderer)
                 rtcTrack.addSink(renderer)
             }
             }
         }
         }
+    }
 
 
     /**
     /**
      * Remove a previously added [VideoSink].
      * Remove a previously added [VideoSink].
      */
      */
     open fun removeRenderer(renderer: VideoSink) {
     open fun removeRenderer(renderer: VideoSink) {
         executeBlockingOnRTCThread {
         executeBlockingOnRTCThread {
+            if (!isDisposed) {
                 rtcTrack.removeSink(renderer)
                 rtcTrack.removeSink(renderer)
                 sinks.remove(renderer)
                 sinks.remove(renderer)
             }
             }
         }
         }
+    }
 
 
     override fun stop() {
     override fun stop() {
         executeBlockingOnRTCThread {
         executeBlockingOnRTCThread {
+            if (!isDisposed) {
                 for (sink in sinks) {
                 for (sink in sinks) {
                     rtcTrack.removeSink(sink)
                     rtcTrack.removeSink(sink)
                 }
                 }
+            }
             sinks.clear()
             sinks.clear()
         }
         }
         super.stop()
         super.stop()