Ensure expected ordering of playlist and playback events. Closes: #959.

src/libaudcore/eventqueue.cc

@@ -46,6 +46,7 @@ struct Event : public ListNode
 };
 
 static aud::mutex mutex;
+static bool paused;
 static List<Event> events;
 static QueuedFunc queued_events;
 
@@ -54,7 +55,7 @@ static void events_execute(void *)
     auto mh = mutex.take();
 
     Event * event;
-    while ((event = events.head()))
+    while (!paused && (event = events.head()))
     {
         events.remove(event);
 
@@ -72,7 +73,7 @@ EXPORT void event_queue(const char * name, void * data,
 {
     auto mh = mutex.take();
 
-    if (!events.head())
+    if (!paused && !events.head())
         queued_events.queue(events_execute, nullptr);
 
     events.append(new Event(name, data, destroy));
@@ -97,6 +98,26 @@ EXPORT void event_queue_cancel(const char * name, void * data)
     }
 }
 
+// this is only for use by the playlist, to ensure that queued playlist
+// updates are processed before generic events
+void event_queue_pause()
+{
+    auto mh = mutex.take();
+    if (!paused)
+        queued_events.stop();
+
+    paused = true;
+}
+
+void event_queue_unpause()
+{
+    auto mh = mutex.take();
+    if (paused && events.head())
+        queued_events.queue(events_execute, nullptr);
+
+    paused = false;
+}
+
 void event_queue_cancel_all()
 {
     auto mh = mutex.take();

src/libaudcore/internal.h

@@ -77,6 +77,8 @@ void eq_set_format(int new_channels, int new_rate);
 void eq_filter(float * data, int samples);
 
 /* eventqueue.cc */
+void event_queue_pause();
+void event_queue_unpause();
 void event_queue_cancel_all();
 
 /* fft.cc */

src/libaudcore/playlist.cc

@@ -189,6 +189,7 @@ static void update(void *)
     update_hooks = 0;
     update_level = Playlist::NoUpdate;
     update_state = UpdateState::None;
+    event_queue_unpause();
 
     mh.unlock();
 
@@ -208,6 +209,16 @@ static void update(void *)
         hook_call("playback stop", nullptr);
 }
 
+static void queue_update()
+{
+    if (update_state < UpdateState::Queued)
+    {
+        event_queue_pause(); // give playlist updates priority
+        queued_update.queue(update, nullptr);
+        update_state = UpdateState::Queued;
+    }
+}
+
 static void queue_update_hooks(int hooks)
 {
     if ((hooks & PlaybackBegin))
@@ -216,12 +227,7 @@ static void queue_update_hooks(int hooks)
         update_hooks &= ~PlaybackBegin;
 
     update_hooks |= hooks;
-
-    if (update_state < UpdateState::Queued)
-    {
-        queued_update.queue(update, nullptr);
-        update_state = UpdateState::Queued;
-    }
+    queue_update();
 }
 
 static void queue_global_update(Playlist::UpdateLevel level, int flags = 0)
@@ -239,11 +245,7 @@ static void queue_global_update(Playlist::UpdateLevel level, int flags = 0)
     }
     else
     {
-        if (update_state < UpdateState::Queued)
-        {
-            queued_update.queue(update, nullptr);
-            update_state = UpdateState::Queued;
-        }
+        queue_update();
     }
 
     update_level = aud::max(update_level, level);
@@ -325,10 +327,7 @@ static void scan_check_complete(PlaylistData * playlist)
     playlist->scan_status = PlaylistData::NotScanning;
 
     if (update_state == UpdateState::Delayed)
-    {
-        queued_update.queue(update, nullptr);
-        update_state = UpdateState::Queued;
-    }
+        queue_update();
 
     event_queue_cancel("playlist scan complete");
     event_queue("playlist scan complete", nullptr);
@@ -497,11 +496,7 @@ void pl_signal_entry_deleted(PlaylistEntry * entry) { scan_cancel(entry); }
 
 void pl_signal_position_changed(Playlist::ID * id)
 {
-    if (update_state < UpdateState::Queued)
-    {
-        queued_update.queue(update, nullptr);
-        update_state = UpdateState::Queued;
-    }
+    queue_update();
 
     if (id == playing_id)
     {
@@ -615,6 +610,7 @@ void playlist_clear_updates()
     update_level = Playlist::NoUpdate;
     update_hooks = 0;
     update_state = UpdateState::None;
+    event_queue_unpause();
 }
 
 void playlist_end()