Do AddOrUpdateSongs in database thread

src/collection/collectionbackend.cpp

@@ -411,6 +411,10 @@ void CollectionBackend::AddOrUpdateSubdirs(const SubdirectoryList &subdirs) {
 
 }
 
+void CollectionBackend::AddOrUpdateSongsAsync(const SongList &songs) {
+  metaObject()->invokeMethod(this, "AddOrUpdateSongs", Qt::QueuedConnection, Q_ARG(SongList, songs));
+}
+
 void CollectionBackend::AddOrUpdateSongs(const SongList &songs) {
 
   QMutexLocker l(db_->Mutex());

src/collection/collectionbackend.h

@@ -186,6 +186,8 @@ class CollectionBackend : public CollectionBackendInterface {
 
   Song::Source Source() const;
 
+  void AddOrUpdateSongsAsync(const SongList &songs);
+
  public slots:
   void Exit();
   void LoadDirectories();