Safely close database connections and delete backends

Also fix NewClosure leak caused by disconnected object signals

src/playlist/playlistbackend.cpp

@@ -20,8 +20,11 @@
 
 #include <memory>
 #include <functional>
+#include <assert.h>
 
 #include <QObject>
+#include <QApplication>
+#include <QThread>
 #include <QMutex>
 #include <QIODevice>
 #include <QDir>
@@ -56,7 +59,36 @@ using std::shared_ptr;
 const int PlaylistBackend::kSongTableJoins = 2;
 
 PlaylistBackend::PlaylistBackend(Application *app, QObject *parent)
-    : QObject(parent), app_(app), db_(app_->database()) {}
+    : QObject(parent), app_(app), db_(app_->database()), original_thread_(nullptr) {
+
+  original_thread_ = thread();
+
+}
+
+PlaylistBackend::~PlaylistBackend() {}
+
+void PlaylistBackend::Close() {
+
+  if (db_) {
+    QMutexLocker l(db_->Mutex());
+    db_->Close();
+  }
+
+}
+
+void PlaylistBackend::ExitAsync() {
+  metaObject()->invokeMethod(this, "Exit", Qt::QueuedConnection);
+}
+
+void PlaylistBackend::Exit() {
+
+  assert(QThread::currentThread() == thread());
+
+  Close();
+  moveToThread(original_thread_);
+  emit ExitFinished();
+
+}
 
 PlaylistBackend::PlaylistList PlaylistBackend::GetAllPlaylists() {
   return GetPlaylists(GetPlaylists_All);
@@ -157,6 +189,10 @@ QSqlQuery PlaylistBackend::GetPlaylistRows(int playlist) {
   q.bindValue(":playlist", playlist);
   q.exec();
 
+  if (QThread::currentThread() != thread() && QThread::currentThread() != qApp->thread()) {
+    db_->Close();
+  }
+
   return q;
 
 }

src/playlist/playlistbackend.h

@@ -39,6 +39,7 @@
 #include "collection/sqlrow.h"
 #include "playlistitem.h"
 
+class QThread;
 class Application;
 class Database;
 
@@ -47,6 +48,7 @@ class PlaylistBackend : public QObject {
 
  public:
   Q_INVOKABLE PlaylistBackend(Application *app, QObject *parent = nullptr);
+  ~PlaylistBackend();
 
   struct Playlist {
     Playlist() : id(-1), favorite(false), last_played(0) {}
@@ -62,6 +64,9 @@ class PlaylistBackend : public QObject {
 
   static const int kSongTableJoins;
 
+  void Close();
+  void ExitAsync();
+
   PlaylistList GetAllPlaylists();
   PlaylistList GetAllOpenPlaylists();
   PlaylistList GetAllFavoritePlaylists();
@@ -82,8 +87,12 @@ class PlaylistBackend : public QObject {
   Application *app() const { return app_; }
 
  public slots:
+  void Exit();
   void SavePlaylist(int playlist, const PlaylistItemList &items, int last_played);
 
+signals:
+  void ExitFinished();
+
  private:
   struct NewSongFromQueryState {
     QHash<QString, SongList> cached_cues_;
@@ -105,6 +114,7 @@ class PlaylistBackend : public QObject {
 
   Application *app_;
   Database *db_;
+  QThread *original_thread_;
 };
 
 #endif  // PLAYLISTBACKEND_H

src/playlist/playlistdelegates.cpp

@@ -22,6 +22,7 @@
 #include "config.h"
 
 #include <QtGlobal>
+#include <QApplication>
 #include <QObject>
 #include <QWidget>
 #include <QtConcurrentRun>
@@ -363,6 +364,10 @@ TagCompletionModel::TagCompletionModel(CollectionBackend *backend, Playlist::Col
     setStringList(backend->GetAll(col));
   }
 
+  if (QThread::currentThread() != backend->thread() && QThread::currentThread() != qApp->thread()) {
+    backend->Close();
+  }
+
 }
 
 QString TagCompletionModel::database_column(Playlist::Column column) {

src/playlist/playlistview.h

@@ -80,6 +80,7 @@ class PlaylistHeader;
 class PlaylistProxyStyle : public QProxyStyle {
 public:
   PlaylistProxyStyle(QStyle *base);
+
   void drawControl(ControlElement element, const QStyleOption *option, QPainter *painter, const QWidget *widget) const;
   void drawPrimitive(PrimitiveElement element, const QStyleOption *option, QPainter *painter, const QWidget *widget) const;