Fix a data race between the feeder thread and attaching of the stream…

… to the mixer.

This is done by by ensuring the stream is pre-filled before attaching is
possible.

Possibly related to #1561

addons/acodec/helper.c

@@ -11,19 +11,23 @@ void _al_acodec_start_feed_thread(ALLEGRO_AUDIO_STREAM *stream)
  stream->feed_thread_started_cond = al_create_cond();
  stream->feed_thread_started_mutex = al_create_mutex();
  al_start_thread(stream->feed_thread);
-}
-
-void _al_acodec_stop_feed_thread(ALLEGRO_AUDIO_STREAM *stream)
-{
- ALLEGRO_EVENT quit_event;
 
  /* Need to wait for the thread to start, otherwise the quit event may be
- * sent before the event source is registered with the queue. */
+ * sent before the event source is registered with the queue.
+ *
+ * This also makes the pre-fill system thread safe, as it needs to operate
+ * before the mutexes are set up.
+ */
  al_lock_mutex(stream->feed_thread_started_mutex);
  while (!stream->feed_thread_started) {
  al_wait_cond(stream->feed_thread_started_cond, stream->feed_thread_started_mutex);
  }
  al_unlock_mutex(stream->feed_thread_started_mutex);
+}
+
+void _al_acodec_stop_feed_thread(ALLEGRO_AUDIO_STREAM *stream)
+{
+ ALLEGRO_EVENT quit_event;
 
  quit_event.type = _KCM_STREAM_FEEDER_QUIT_EVENT_TYPE;
  al_emit_user_event(al_get_audio_stream_event_source(stream), &quit_event, NULL);

addons/audio/kcm_stream.c

@@ -692,11 +692,6 @@ void *_al_kcm_feed_stream(ALLEGRO_THREAD *self, void *vstream)
  queue = al_create_event_queue();
  al_register_event_source(queue, &stream->spl.es);
 
- al_lock_mutex(stream->feed_thread_started_mutex);
- stream->feed_thread_started = true;
- al_broadcast_cond(stream->feed_thread_started_cond);
- al_unlock_mutex(stream->feed_thread_started_mutex);
-
  stream->quit_feed_thread = false;
 
  while (!stream->quit_feed_thread) {
@@ -708,7 +703,6 @@ void *_al_kcm_feed_stream(ALLEGRO_THREAD *self, void *vstream)
 
  if ((prefill || event.type == ALLEGRO_EVENT_AUDIO_STREAM_FRAGMENT)
  && !stream->is_draining) {
- prefill = false;
  unsigned long bytes;
  unsigned long bytes_written;
  ALLEGRO_MUTEX *stream_mutex;
@@ -784,6 +778,13 @@ void *_al_kcm_feed_stream(ALLEGRO_THREAD *self, void *vstream)
  fin_event.user.timestamp = al_get_time();
  al_emit_user_event(&stream->spl.es, &fin_event, NULL);
  }
+ if (prefill) {
+ al_lock_mutex(stream->feed_thread_started_mutex);
+ stream->feed_thread_started = true;
+ al_broadcast_cond(stream->feed_thread_started_cond);
+ al_unlock_mutex(stream->feed_thread_started_mutex);
+ }
+ prefill = false;
  }
 
  al_destroy_event_queue(queue);