fix: thread-safe player position logging

app/src/main/java/at/lockstep/player/playback/PlaybackService.kt

@@ -50,6 +50,7 @@ class PlaybackService : Service() {
 
     private var player: ExoPlayer? = null
     private var positionPollJob: Job? = null
+    private var positionCachePollJob: Job? = null
 
     private val _uiState = MutableStateFlow(PlaybackUiState.initial())
     val uiState: StateFlow<PlaybackUiState> = _uiState.asStateFlow()
@@ -64,6 +65,10 @@ class PlaybackService : Service() {
     private var queue: List<TrackQueueItem> = emptyList()
     private var index: Int = 0
 
+    /** Updated on the main thread whenever progress is read from ExoPlayer — safe for sensor threads. */
+    @Volatile
+    private var cachedPlaybackPositionMs: Long = 0L
+
     private val playerListener =
         object : Player.Listener {
             override fun onPlaybackStateChanged(playbackState: Int) {
@@ -215,11 +220,21 @@ class PlaybackService : Service() {
                     }
                 }
             }
+        positionCachePollJob?.cancel()
+        positionCachePollJob =
+            scope.launch {
+                while (isActive) {
+                    delay(POSITION_CACHE_INTERVAL_MS)
+                    refreshCachedPlaybackPositionMs()
+                }
+            }
     }
 
     private fun releasePlayer() {
         positionPollJob?.cancel()
         positionPollJob = null
+        positionCachePollJob?.cancel()
+        positionCachePollJob = null
         player?.removeListener(playerListener)
         player?.release()
         player = null
@@ -321,13 +336,24 @@ class PlaybackService : Service() {
         return hint
     }
 
+    private fun refreshCachedPlaybackPositionMs() {
+        val p = player ?: return
+        if (queue.isEmpty()) {
+            cachedPlaybackPositionMs = 0L
+            return
+        }
+        val durationMs = currentDurationMs().coerceAtLeast(1L)
+        cachedPlaybackPositionMs = p.currentPosition.coerceIn(0L, durationMs)
+    }
+
     private fun updateProgressFromPlayer() {
         val p = player ?: return
-        val durationMs = currentDurationMs().coerceAtLeast(1L)
-        val positionMs = p.currentPosition.coerceIn(0L, durationMs)
+        refreshCachedPlaybackPositionMs()
         if (queue.isEmpty()) {
             return
         }
+        val durationMs = currentDurationMs().coerceAtLeast(1L)
+        val positionMs = cachedPlaybackPositionMs
         val progress = (positionMs.toFloat() / durationMs.toFloat()).coerceIn(0f, 1f)
         val durationSec = (durationMs / 1000L).toInt().coerceAtLeast(1)
         _uiState.value =
@@ -413,11 +439,9 @@ class PlaybackService : Service() {
 
     /**
      * Milliseconds from the start of the current track — same timebase as [ExoPlayer.getCurrentPosition].
-     * May be called from any thread per Media3 [Player] contract.
+     * Reads a main-thread cache so callers on background threads (e.g. run-data sensor collection) stay safe.
      */
-    fun getPlaybackPositionMs(): Long {
-        return player?.currentPosition ?: 0L
-    }
+    fun getPlaybackPositionMs(): Long = cachedPlaybackPositionMs
 
     private fun refreshForegroundNotification() {
         if (queue.isEmpty()) return
@@ -494,6 +518,7 @@ class PlaybackService : Service() {
 
     override fun onDestroy() {
         positionPollJob?.cancel()
+        positionCachePollJob?.cancel()
         releasePlayer()
         mediaSession.run {
             isActive = false
@@ -538,6 +563,7 @@ class PlaybackService : Service() {
 
     companion object {
         private const val UPDATE_INTERVAL_MS = 250L
+        private const val POSITION_CACHE_INTERVAL_MS = 20L
         private const val DEFAULT_DURATION_HINT_MS = 180_000
 
         const val ACTION_START_PLAYLIST = "at.lockstep.player.action.START_PLAYLIST"