Top level values can be only accessed from the main thread. (#1922)

samples/videoplayer/src/main/kotlin/DecoderWorker.kt

@@ -20,6 +20,7 @@ import kotlinx.cinterop.*
 import platform.posix.memcpy
 
 // This global variable only set to != null value in the decoding worker.
+@ThreadLocal
 private var decoder: Decoder? = null
 
 data class VideoInfo(val size: Dimensions, val fps: Double)

samples/videoplayer/src/main/kotlin/SDLAudio.kt

@@ -76,6 +76,7 @@ class SDLAudio(val player: VideoPlayer) : DisposableContainer() {
 }
 
 // Only set in the audio thread
+@ThreadLocal
 private var decoder: DecoderWorker? = null
 
 private fun audioCallback(userdata: COpaquePointer?, buffer: CPointer<Uint8Var>?, length: Int) {