Safely close database connections and delete backends

Also fix NewClosure leak caused by disconnected object signals

ext/libstrawberry-common/core/closure.cpp

@@ -22,6 +22,7 @@
 
 #include "closure.h"
 
+#include "core/logging.h"
 #include "core/timeconstants.h"
 
 namespace _detail {
@@ -30,8 +31,7 @@ ClosureBase::ClosureBase(ObjectHelper *helper)
     : helper_(helper) {
 }
 
-ClosureBase::~ClosureBase() {
+ClosureBase::~ClosureBase() {}
-}
 
 CallbackClosure::CallbackClosure(QObject *sender, const char *signal, std::function<void()> callback)
     : ClosureBase(new ObjectHelper(sender, signal, this)),
@@ -53,6 +53,8 @@ ObjectHelper::ObjectHelper(QObject *sender, const char *signal, ClosureBase *clo
 
 }
 
+ObjectHelper::~ObjectHelper() {}
+
 void ObjectHelper::Invoked() {
   closure_->Invoke();
   deleteLater();

ext/libstrawberry-common/core/closure.h

@@ -34,6 +34,8 @@
 #include <QList>
 #include <QTimer>
 
+#include "core/logging.h"
+
 namespace _detail {
 
 class ObjectHelper;
@@ -62,6 +64,7 @@ class ObjectHelper : public QObject {
   Q_OBJECT
  public:
   ObjectHelper(QObject *parent, const char *signal, ClosureBase *closure);
+  ~ObjectHelper();
 
  private slots:
   void Invoked();

src/collection/collection.cpp

@@ -21,6 +21,7 @@
 #include "config.h"
 
 #include <stdbool.h>
+#include <unistd.h>
 
 #include <QObject>
 #include <QThread>
@@ -50,7 +51,10 @@ SCollection::SCollection(Application *app, QObject *parent)
       backend_(nullptr),
       model_(nullptr),
       watcher_(nullptr),
-      watcher_thread_(nullptr) {
+      watcher_thread_(nullptr),
+      original_thread_(nullptr) {
+
+  original_thread_ = thread();
 
   backend_ = new CollectionBackend();
   backend()->moveToThread(app->database()->thread());
@@ -64,11 +68,17 @@ SCollection::SCollection(Application *app, QObject *parent)
 }
 
 SCollection::~SCollection() {
+
+  if (watcher_) {
     watcher_->Stop();
     watcher_->deleteLater();
+  }
+  if (watcher_thread_) {
     watcher_thread_->exit();
     watcher_thread_->wait(5000 /* five seconds */);
+  }
   backend_->deleteLater();
+
 }
 
 void SCollection::Init() {
@@ -98,6 +108,29 @@ void SCollection::Init() {
 
   // This will start the watcher checking for updates
   backend_->LoadDirectoriesAsync();
+
+}
+
+void SCollection::Exit() {
+
+  wait_for_exit_ << backend_ << watcher_;
+
+  disconnect(backend_, 0, watcher_, 0);
+  disconnect(watcher_, 0, backend_, 0);
+
+  connect(backend_, SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  connect(watcher_, SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  backend_->ExitAsync();
+  watcher_->ExitAsync();
+
+}
+
+void SCollection::ExitReceived() {
+
+  disconnect(sender(), 0, this, 0);
+  wait_for_exit_.removeAll(sender());
+  if (wait_for_exit_.isEmpty()) emit ExitFinished();
+
 }
 
 void SCollection::IncrementalScan() { watcher_->IncrementalScanAsync(); }

src/collection/collection.h

@@ -49,6 +49,7 @@ class SCollection : public QObject {
   static const char *kFtsTable;
 
   void Init();
+  void Exit();
 
   CollectionBackend *backend() const { return backend_; }
   CollectionModel *model() const { return model_; }
@@ -70,12 +71,17 @@ class SCollection : public QObject {
   void Rescan(const SongList &songs);
 
  private slots:
+  void ExitReceived();
+
   void IncrementalScan();
 
   void CurrentSongChanged(const Song &song);
   void SongsStatisticsChanged(const SongList& songs);
   void Stopped();
 
+ signals:
+  void ExitFinished();
+
  private:
   Application *app_;
   CollectionBackend *backend_;
@@ -83,9 +89,12 @@ class SCollection : public QObject {
 
   CollectionWatcher *watcher_;
   Thread *watcher_thread_;
+  QThread *original_thread_;
 
   // DB schema versions which should trigger a full collection rescan (each of those with a short reason why).
   QHash<int, QString> full_rescan_revisions_;
+
+  QList<QObject*> wait_for_exit_;
 };
 
 #endif

src/collection/collectionbackend.cpp

@@ -20,8 +20,12 @@
 
 #include "config.h"
 
+#include <assert.h>
+
 #include <QtGlobal>
 #include <QObject>
+#include <QApplication>
+#include <QThread>
 #include <QMutex>
 #include <QSet>
 #include <QMap>
@@ -52,7 +56,14 @@ const char *CollectionBackend::kSettingsGroup = "Collection";
 
 CollectionBackend::CollectionBackend(QObject *parent) :
     CollectionBackendInterface(parent),
-    db_(nullptr) {}
+    db_(nullptr),
+    original_thread_(nullptr) {
+
+  original_thread_ = thread();
+
+}
+
+CollectionBackend::~CollectionBackend() {}
 
 void CollectionBackend::Init(Database *db, const Song::Source source, const QString &songs_table, const QString &dirs_table, const QString &subdirs_table, const QString &fts_table) {
   db_ = db;
@@ -63,6 +74,29 @@ void CollectionBackend::Init(Database *db, const Song::Source source, const QStr
   fts_table_ = fts_table;
 }
 
+void CollectionBackend::Close() {
+
+  if (db_) {
+    QMutexLocker l(db_->Mutex());
+    db_->Close();
+  }
+
+}
+
+void CollectionBackend::ExitAsync() {
+  metaObject()->invokeMethod(this, "Exit", Qt::QueuedConnection);
+}
+
+void CollectionBackend::Exit() {
+
+  assert(QThread::currentThread() == thread());
+
+  Close();
+  moveToThread(original_thread_);
+  emit ExitFinished();
+
+}
+
 void CollectionBackend::LoadDirectoriesAsync() {
   metaObject()->invokeMethod(this, "LoadDirectories", Qt::QueuedConnection);
 }

src/collection/collectionbackend.h

@@ -41,6 +41,7 @@
 #include "collectionquery.h"
 #include "directory.h"
 
+class QThread;
 class Database;
 
 class CollectionBackendInterface : public QObject {
@@ -123,7 +124,12 @@ class CollectionBackend : public CollectionBackendInterface {
   static const char *kSettingsGroup;
 
   Q_INVOKABLE CollectionBackend(QObject *parent = nullptr);
+  ~CollectionBackend();
+
   void Init(Database *db, const Song::Source source, const QString &songs_table, const QString &dirs_table, const QString &subdirs_table, const QString &fts_table);
+  void Close();
+
+  void ExitAsync();
 
   Database *db() const { return db_; }
 
@@ -183,6 +189,7 @@ class CollectionBackend : public CollectionBackendInterface {
   SongList GetSongsBySongId(const QStringList &song_ids);
 
  public slots:
+  void Exit();
   void LoadDirectories();
   void UpdateTotalSongCount();
   void UpdateTotalArtistCount();
@@ -200,7 +207,7 @@ class CollectionBackend : public CollectionBackendInterface {
   void ResetStatistics(int id);
   void SongPathChanged(const Song &song, const QFileInfo &new_file);
 
-signals:
+ signals:
   void DirectoryDiscovered(const Directory &dir, const SubdirectoryList &subdirs);
   void DirectoryDeleted(const Directory &dir);
 
@@ -214,6 +221,8 @@ signals:
   void TotalArtistCountUpdated(int total);
   void TotalAlbumCountUpdated(int total);
 
+  void ExitFinished();
+
  private:
   struct CompilationInfo {
     CompilationInfo() : has_compilation_detected(false), has_not_compilation_detected(false) {}
@@ -243,6 +252,7 @@ signals:
   QString dirs_table_;
   QString subdirs_table_;
   QString fts_table_;
+  QThread *original_thread_;
 
 };
 

src/collection/collectionmodel.cpp

@@ -129,7 +129,10 @@ CollectionModel::CollectionModel(CollectionBackend *backend, Application *app, Q
 
 }
 
-CollectionModel::~CollectionModel() { delete root_; }
+CollectionModel::~CollectionModel() {
+  backend_->Close();
+  delete root_;
+}
 
 void CollectionModel::set_pretty_covers(bool use_pretty_covers) {
 
@@ -757,6 +760,11 @@ CollectionModel::QueryResult CollectionModel::RunQuery(CollectionItem *parent) {
   while (q.Next()) {
     result.rows << SqlRow(q);
   }
+
+  if (QThread::currentThread() != thread() && QThread::currentThread() != backend_->thread()) {
+    backend_->Close();
+  }
+
   return result;
 
 }

src/collection/collectionwatcher.cpp

@@ -20,7 +20,11 @@
 
 #include "config.h"
 
+#include <assert.h>
+
 #include <QObject>
+#include <QApplication>
+#include <QThread>
 #include <QIODevice>
 #include <QDir>
 #include <QDirIterator>
@@ -79,7 +83,10 @@ CollectionWatcher::CollectionWatcher(Song::Source source, QObject *parent)
       rescan_timer_(new QTimer(this)),
       rescan_paused_(false),
       total_watches_(0),
-      cue_parser_(new CueParser(backend_, this)) {
+      cue_parser_(new CueParser(backend_, this)),
+      original_thread_(nullptr) {
+
+  original_thread_ = thread();
 
   rescan_timer_->setInterval(1000);
   rescan_timer_->setSingleShot(true);
@@ -93,6 +100,21 @@ CollectionWatcher::CollectionWatcher(Song::Source source, QObject *parent)
   connect(rescan_timer_, SIGNAL(timeout()), SLOT(RescanPathsNow()));
 }
 
+void CollectionWatcher::ExitAsync() {
+  metaObject()->invokeMethod(this, "Exit", Qt::QueuedConnection);
+}
+
+void CollectionWatcher::Exit() {
+
+  assert(QThread::currentThread() == thread());
+
+  Stop();
+  if (backend_) backend_->Close();
+  moveToThread(original_thread_);
+  emit ExitFinished();
+
+}
+
 CollectionWatcher::ScanTransaction::ScanTransaction(CollectionWatcher *watcher, const int dir, const bool incremental, const bool ignores_mtime, const bool prevent_delete)
     : progress_(0),
       progress_max_(0),

src/collection/collectionwatcher.h

@@ -60,6 +60,8 @@ class CollectionWatcher : public QObject {
 
   void Stop() { stop_requested_ = true; }
 
+  void ExitAsync();
+
 signals:
   void NewOrUpdatedSongs(const SongList &songs);
   void SongsMTimeUpdated(const SongList &songs);
@@ -68,6 +70,7 @@ signals:
   void SubdirsDiscovered(const SubdirectoryList &subdirs);
   void SubdirsMTimeUpdated(const SubdirectoryList &subdirs);
   void CompilationsNeedUpdating();
+  void ExitFinished();
 
   void ScanStarted(int task_id);
 
@@ -142,6 +145,7 @@ signals:
   };
 
  private slots:
+  void Exit();
   void DirectoryChanged(const QString &path);
   void IncrementalScanNow();
   void FullScanNow();
@@ -204,6 +208,8 @@ signals:
 
   SongList song_rescan_queue_; // Set by ui thread
 
+  QThread *original_thread_;
+
 };
 
 inline QString CollectionWatcher::NoExtensionPart(const QString& fileName) {

src/core/application.cpp

@@ -223,10 +223,12 @@ Application::~Application() {
 
   for (QThread *thread : threads_) {
     thread->wait();
+    thread->deleteLater();
   }
+
 }
 
-void Application::MoveToNewThread(QObject *object) {
+QThread *Application::MoveToNewThread(QObject *object) {
 
   QThread *thread = new QThread(this);
 
@@ -234,6 +236,9 @@ void Application::MoveToNewThread(QObject *object) {
 
   thread->start();
   threads_ << thread;
+
+  return thread;
+
 }
 
 void Application::MoveToThread(QObject *object, QThread *thread) {
@@ -241,6 +246,38 @@ void Application::MoveToThread(QObject *object, QThread *thread) {
   object->moveToThread(thread);
 }
 
+void Application::Exit() {
+
+  wait_for_exit_ << collection()
+                 << playlist_backend()
+                 << device_manager()
+                 << internet_services();
+
+  connect(collection(), SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  collection()->Exit();
+
+  connect(playlist_backend(), SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  playlist_backend()->ExitAsync();
+
+  connect(device_manager(), SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  device_manager()->Exit();
+
+  connect(internet_services(), SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  internet_services()->Exit();
+
+  database()->Close();
+
+}
+
+void Application::ExitReceived() {
+
+  disconnect(sender(), 0, this, 0);
+
+  wait_for_exit_.removeAll(sender());
+  if (wait_for_exit_.isEmpty()) emit ExitFinished();
+
+}
+
 void Application::AddError(const QString& message) { emit ErrorAdded(message); }
 void Application::ReloadSettings() { emit SettingsChanged(); }
 void Application::OpenSettingsDialogAtPage(SettingsDialog::Page page) { emit SettingsDialogRequested(page); }

src/core/application.h

@@ -111,9 +111,14 @@ class Application : public QObject {
   MoodbarLoader *moodbar_loader() const;
 #endif
 
-  void MoveToNewThread(QObject *object);
+  void Exit();
+
+  QThread *MoveToNewThread(QObject *object);
   void MoveToThread(QObject *object, QThread *thread);
 
+private slots:
+  void ExitReceived();
+
  public slots:
   void AddError(const QString &message);
   void ReloadSettings();
@@ -123,10 +128,12 @@ signals:
   void ErrorAdded(const QString &message);
   void SettingsChanged();
   void SettingsDialogRequested(SettingsDialog::Page page);
+  void ExitFinished();
 
  private:
   std::unique_ptr<ApplicationImpl> p_;
   QList<QThread*> threads_;
+  QList<QObject*> wait_for_exit_;
 
 };
 

src/core/database.cpp

@@ -211,6 +211,7 @@ int Database::FTSNext(sqlite3_tokenizer_cursor *cursor, const char* *token, int
 void Database::StaticInit() {
 
   if (sFTSTokenizer) return;
+
   sFTSTokenizer = new sqlite3_tokenizer_module;
   sFTSTokenizer->iVersion = 0;
   sFTSTokenizer->xCreate = &Database::FTSCreate;
@@ -242,7 +243,21 @@ Database::Database(Application *app, QObject *parent, const QString &database_na
 
 }
 
-Database::~Database() {}
+Database::~Database() {
+
+  QMutexLocker l(&connect_mutex_);
+
+  for (QString connection : connections_) {
+    qLog(Error) << connection << "still open!";
+  }
+
+  if (!connections_.isEmpty())
+    qLog(Error) << connections_.count() << "connections still open!";
+
+  if (sFTSTokenizer)
+    delete sFTSTokenizer;
+
+}
 
 QSqlDatabase Database::Connect() {
 
@@ -257,6 +272,11 @@ QSqlDatabase Database::Connect() {
 
   const QString connection_id = QString("%1_thread_%2").arg(connection_id_).arg(reinterpret_cast<quint64>(QThread::currentThread()));
 
+  if (!connections_.contains(connection_id)) {
+    //qLog(Debug) << "Opened database with connection id" << connection_id;
+    connections_ << connection_id;
+  }
+
   // Try to find an existing connection for this thread
   QSqlDatabase db = QSqlDatabase::database(connection_id);
   if (db.isOpen()) {
@@ -346,6 +366,25 @@ QSqlDatabase Database::Connect() {
 
 }
 
+void Database::Close() {
+
+  QMutexLocker l(&connect_mutex_);
+
+  const QString connection_id = QString("%1_thread_%2").arg(connection_id_).arg(reinterpret_cast<quint64>(QThread::currentThread()));
+
+  // Try to find an existing connection for this thread
+  QSqlDatabase db = QSqlDatabase::database(connection_id);
+  if (db.isOpen()) {
+    db.close();
+  }
+
+  if (connections_.contains(connection_id)) {
+    //qLog(Debug) << "Closed database with connection id" << connection_id;
+    connections_.removeAll(connection_id);
+  }
+
+}
+
 void Database::UpdateMainSchema(QSqlDatabase *db) {
 
   // Get the database's schema version

src/core/database.h

@@ -68,6 +68,7 @@ class Database : public QObject {
   static const char *kMagicAllSongsTables;
 
   QSqlDatabase Connect();
+  void Close();
   bool CheckErrors(const QSqlQuery &query);
   QMutex *Mutex() { return &mutex_; }
 
@@ -111,6 +112,7 @@ signals:
 
   // This ID makes the QSqlDatabase name unique to the object as well as the thread
   int connection_id_;
+  QStringList connections_;
 
   static QMutex sNextConnectionIdMutex;
   static int sNextConnectionId;

src/core/deletefiles.cpp

@@ -55,7 +55,7 @@ void DeleteFiles::Start(const SongList &songs) {
   task_id_ = task_manager_->StartTask(tr("Deleting files"));
   task_manager_->SetTaskBlocksCollectionScans(true);
 
-  thread_ = new QThread;
+  thread_ = new QThread(this);
   connect(thread_, SIGNAL(started()), SLOT(ProcessSomeFiles()));
 
   moveToThread(thread_);

src/core/mainwindow.cpp

@@ -989,7 +989,7 @@ void MainWindow::Exit() {
 
   if (app_->player()->engine()->is_fadeout_enabled()) {
     // To shut down the application when fadeout will be finished
-    connect(app_->player()->engine(), SIGNAL(FadeoutFinishedSignal()), qApp, SLOT(quit()));
+    connect(app_->player()->engine(), SIGNAL(FadeoutFinishedSignal()), this, SLOT(DoExit()));
     if (app_->player()->GetState() == Engine::Playing) {
       app_->player()->Stop();
       hide();
@@ -998,6 +998,19 @@ void MainWindow::Exit() {
     }
   }
 
+  DoExit();
+
+}
+
+void MainWindow::DoExit() {
+
+  connect(app_, SIGNAL(ExitFinished()), this, SLOT(ExitFinished()));
+  app_->Exit();
+
+}
+
+void MainWindow::ExitFinished() {
+
   qApp->quit();
 
 }

src/core/mainwindow.h

@@ -243,6 +243,7 @@ signals:
   void Raise();
 
   void Exit();
+  void DoExit();
 
   void HandleNotificationPreview(OSD::Behaviour type, QString line1, QString line2);
 
@@ -262,6 +263,8 @@ signals:
   void LoveButtonVisibilityChanged(bool value);
   void Love();
 
+  void ExitFinished();
+
  private:
 
   void SaveSettings();

src/covermanager/currentalbumcoverloader.cpp

@@ -52,7 +52,10 @@ CurrentAlbumCoverLoader::CurrentAlbumCoverLoader(Application *app, QObject *pare
 
 }
 
-CurrentAlbumCoverLoader::~CurrentAlbumCoverLoader() {}
+CurrentAlbumCoverLoader::~CurrentAlbumCoverLoader() {
+  if (temp_cover_) temp_cover_->remove();
+  if (temp_cover_thumbnail_) temp_cover_thumbnail_->remove();
+}
 
 void CurrentAlbumCoverLoader::LoadAlbumCover(const Song &song) {
   last_song_ = song;

src/device/devicedatabasebackend.cpp

@@ -18,9 +18,14 @@
  *
  */
 
+#include "config.h"
+
 #include <stdbool.h>
+#include <assert.h>
 
 #include <QObject>
+#include <QApplication>
+#include <QThread>
 #include <QMutex>
 #include <QIODevice>
 #include <QFile>
@@ -32,17 +37,47 @@
 
 #include "core/database.h"
 #include "core/scopedtransaction.h"
+#include "core/logging.h"
 #include "devicedatabasebackend.h"
 
 const int DeviceDatabaseBackend::kDeviceSchemaVersion = 0;
 
 DeviceDatabaseBackend::DeviceDatabaseBackend(QObject *parent) :
     QObject(parent),
-    db_(nullptr)
+    db_(nullptr),
-    {}
+    original_thread_(nullptr)
+    {
+
+  original_thread_ = thread();
+
+}
+
+DeviceDatabaseBackend::~DeviceDatabaseBackend() {}
 
 void DeviceDatabaseBackend::Init(Database* db) { db_ = db; }
 
+void DeviceDatabaseBackend::Close() {
+
+  if (db_) {
+    QMutexLocker l(db_->Mutex());
+    db_->Close();
+  }
+
+}
+
+void DeviceDatabaseBackend::ExitAsync() {
+  metaObject()->invokeMethod(this, "Exit", Qt::QueuedConnection);
+}
+
+void DeviceDatabaseBackend::Exit() {
+
+  assert(QThread::currentThread() == thread());
+  Close();
+  moveToThread(original_thread_);
+  emit ExitFinished();
+
+}
+
 DeviceDatabaseBackend::DeviceList DeviceDatabaseBackend::GetAllDevices() {
 
   QMutexLocker l(db_->Mutex());
@@ -101,6 +136,7 @@ int DeviceDatabaseBackend::AddDevice(const Device &device) {
   db_->ExecSchemaCommands(db, schema, 0, true);
 
   t.Commit();
+
   return id;
 
 }

src/device/devicedatabasebackend.h

@@ -40,6 +40,7 @@ class DeviceDatabaseBackend : public QObject {
 
  public:
   Q_INVOKABLE DeviceDatabaseBackend(QObject *parent = nullptr);
+  ~DeviceDatabaseBackend();
 
   struct Device {
     Device() : id_(-1) {}
@@ -58,6 +59,9 @@ class DeviceDatabaseBackend : public QObject {
   static const int kDeviceSchemaVersion;
 
   void Init(Database *db);
+  void Close();
+  void ExitAsync();
+
   Database *db() const { return db_; }
 
   DeviceList GetAllDevices();
@@ -66,8 +70,16 @@ class DeviceDatabaseBackend : public QObject {
 
   void SetDeviceOptions(int id, const QString &friendly_name, const QString &icon_name, MusicStorage::TranscodeMode mode, Song::FileType format);
 
+ private slots:
+  void Exit();
+
+ signals:
+  void ExitFinished();
+
  private:
   Database *db_;
+  QThread *original_thread_;
+
 };
 
 #endif  // DEVICEDATABASEBACKEND_H

src/device/devicemanager.cpp

@@ -158,9 +158,17 @@ DeviceManager::~DeviceManager() {
     delete lister;
   }
 
-  backend_->deleteLater();
+  backend_->Close();
 
   delete root_;
+  delete backend_;
+
+}
+
+void DeviceManager::Exit() {
+
+  connect(backend_, SIGNAL(ExitFinished()), this, SIGNAL(ExitFinished()));
+  backend_->ExitAsync();
 
 }
 
@@ -174,6 +182,7 @@ void DeviceManager::LoadAllDevices() {
     info->InitFromDb(device);
     emit DeviceCreatedFromDB(info);
   }
+  backend_->Close();
 
 }
 

src/device/devicemanager.h

@@ -85,6 +85,8 @@ class DeviceManager : public SimpleTreeModel<DeviceInfo> {
   static const int kDeviceIconSize;
   static const int kDeviceIconOverlaySize;
 
+  void Exit();
+
   DeviceStateFilterModel *connected_devices_model() const { return connected_devices_model_; }
 
   // Get info about devices
@@ -115,6 +117,7 @@ class DeviceManager : public SimpleTreeModel<DeviceInfo> {
   void Unmount(QModelIndex idx);
 
  signals:
+  void ExitFinished();
   void DeviceConnected(QModelIndex idx);
   void DeviceDisconnected(QModelIndex idx);
   void DeviceCreatedFromDB(DeviceInfo* info);

src/device/gpodloader.cpp

@@ -102,6 +102,8 @@ Itdb_iTunesDB *GPodLoader::TryLoad() {
   // Add the songs we've just loaded
   backend_->AddOrUpdateSongs(songs);
 
+  backend_->Close();
+
   return db;
 
 }

src/device/mtploader.cpp

@@ -96,6 +96,8 @@ bool MtpLoader::TryLoad() {
   // Add the songs we've just loaded
   backend_->AddOrUpdateSongs(songs);
 
+  backend_->Close();
+
   return true;
 
 }

src/internet/internetservice.h

@@ -40,6 +40,7 @@ class InternetService : public QObject {
   InternetService(Song::Source source, const QString &name, const QString &url_scheme, Application *app, QObject *parent = nullptr);
 
   virtual ~InternetService() {}
+  virtual void Exit() {}
 
   virtual Song::Source source() const { return source_; }
   virtual QString name() const { return name_; }
@@ -75,6 +76,7 @@ class InternetService : public QObject {
   virtual void ResetSongsRequest() {}
 
  signals:
+  void ExitFinished();
   void Login();
   void Logout();
   void Login(const QString &api_token, const QString &username, const QString &password);

src/internet/internetservices.cpp

@@ -72,3 +72,22 @@ void InternetServices::ReloadSettings() {
     service->ReloadSettings();
   }
 }
+
+void InternetServices::Exit() {
+
+  for (InternetService *service : services_.values()) {
+    wait_for_exit_ << service;
+    connect(service, SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+    service->Exit();
+  }
+
+}
+
+void InternetServices::ExitReceived() {
+
+  InternetService *service = qobject_cast<InternetService*>(sender());
+
+  wait_for_exit_.removeAll(service);
+  if (wait_for_exit_.isEmpty()) emit ExitFinished();
+
+}

src/internet/internetservices.h

@@ -47,9 +47,17 @@ class InternetServices : public QObject {
   void AddService(InternetService *service);
   void RemoveService(InternetService *service);
   void ReloadSettings();
+  void Exit();
+
+ signals:
+  void ExitFinished();
+
+ private slots:
+  void ExitReceived();
 
  private:
   QMap<Song::Source, InternetService*> services_;
+  QList<InternetService*> wait_for_exit_;
 
 };
 

src/musicbrainz/musicbrainzclient.cpp

@@ -115,7 +115,7 @@ void MusicBrainzClient::Cancel(int id) {
 
   while (!requests_.isEmpty() && requests_.contains(id)) {
     QNetworkReply *reply = requests_.take(id);
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     if (reply->isRunning()) reply->abort();
     reply->deleteLater();
   }

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;
 

src/qobuz/qobuzbaserequest.cpp

@@ -51,7 +51,7 @@ QobuzBaseRequest::~QobuzBaseRequest() {
 
   while (!replies_.isEmpty()) {
     QNetworkReply *reply = replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     if (reply->isRunning()) reply->abort();
     reply->deleteLater();
   }

src/qobuz/qobuzfavoriterequest.cpp

@@ -49,7 +49,7 @@ QobuzFavoriteRequest::~QobuzFavoriteRequest() {
 
   while (!replies_.isEmpty()) {
     QNetworkReply *reply = replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     reply->abort();
     reply->deleteLater();
   }

src/qobuz/qobuzrequest.cpp

@@ -77,7 +77,7 @@ QobuzRequest::~QobuzRequest() {
 
   while (!album_cover_replies_.isEmpty()) {
     QNetworkReply *reply = album_cover_replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     if (reply->isRunning()) reply->abort();
     reply->deleteLater();
   }

src/qobuz/qobuzservice.cpp

@@ -176,13 +176,35 @@ QobuzService::~QobuzService() {
 
   while (!stream_url_requests_.isEmpty()) {
     QobuzStreamURLRequest *stream_url_req = stream_url_requests_.takeFirst();
-    disconnect(stream_url_req, 0, nullptr, 0);
+    disconnect(stream_url_req, 0, this, 0);
     stream_url_req->deleteLater();
   }
 
-  artists_collection_backend_->deleteLater();
+  delete artists_collection_backend_;
-  albums_collection_backend_->deleteLater();
+  delete albums_collection_backend_;
-  songs_collection_backend_->deleteLater();
+  delete songs_collection_backend_;
+
+}
+
+void QobuzService::Exit() {
+
+  wait_for_exit_ << artists_collection_backend_ << albums_collection_backend_ << songs_collection_backend_;
+
+  connect(artists_collection_backend_, SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  connect(albums_collection_backend_, SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  connect(songs_collection_backend_, SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+
+  artists_collection_backend_->ExitAsync();
+  albums_collection_backend_->ExitAsync();
+  songs_collection_backend_->ExitAsync();
+
+}
+
+void QobuzService::ExitReceived() {
+
+  disconnect(sender(), 0, this, 0);
+  wait_for_exit_.removeAll(sender());
+  if (wait_for_exit_.isEmpty()) emit ExitFinished();
 
 }
 
@@ -395,7 +417,7 @@ void QobuzService::TryLogin() {
 void QobuzService::ResetArtistsRequest() {
 
   if (artists_request_.get()) {
-    disconnect(artists_request_.get(), 0, nullptr, 0);
+    disconnect(artists_request_.get(), 0, this, 0);
     disconnect(this, 0, artists_request_.get(), 0);
     artists_request_.reset();
   }
@@ -446,7 +468,7 @@ void QobuzService::ArtistsUpdateProgressReceived(const int id, const int progres
 void QobuzService::ResetAlbumsRequest() {
 
   if (albums_request_.get()) {
-    disconnect(albums_request_.get(), 0, nullptr, 0);
+    disconnect(albums_request_.get(), 0, this, 0);
     disconnect(this, 0, albums_request_.get(), 0);
     albums_request_.reset();
   }
@@ -495,7 +517,7 @@ void QobuzService::AlbumsUpdateProgressReceived(const int id, const int progress
 void QobuzService::ResetSongsRequest() {
 
   if (songs_request_.get()) {
-    disconnect(songs_request_.get(), 0, nullptr, 0);
+    disconnect(songs_request_.get(), 0, this, 0);
     disconnect(this, 0, songs_request_.get(), 0);
     songs_request_.reset();
   }

src/qobuz/qobuzservice.h

@@ -40,6 +40,7 @@
 #include "internet/internetsearch.h"
 #include "settings/qobuzsettingspage.h"
 
+class QThread;
 class Application;
 class NetworkAccessManager;
 class QobuzUrlHandler;
@@ -60,6 +61,7 @@ class QobuzService : public InternetService {
 
   static const Song::Source kSource;
 
+  void Exit();
   void ReloadSettings();
 
   void Logout();
@@ -123,6 +125,7 @@ class QobuzService : public InternetService {
   void ResetSongsRequest();
 
  private slots:
+  void ExitReceived();
   void SendLogin();
   void HandleLoginSSLErrors(QList<QSslError> ssl_errors);
   void HandleAuthReply(QNetworkReply *reply);
@@ -217,6 +220,8 @@ class QobuzService : public InternetService {
 
   QStringList login_errors_;
 
+  QList<QObject*> wait_for_exit_;
+
 };
 
 #endif  // QOBUZSERVICE_H

src/qobuz/qobuzstreamurlrequest.cpp

@@ -54,7 +54,7 @@ QobuzStreamURLRequest::QobuzStreamURLRequest(QobuzService *service, NetworkAcces
 QobuzStreamURLRequest::~QobuzStreamURLRequest() {
 
   if (reply_) {
-    disconnect(reply_, 0, nullptr, 0);
+    disconnect(reply_, 0, this, 0);
     if (reply_->isRunning()) reply_->abort();
     reply_->deleteLater();
   }
@@ -107,7 +107,7 @@ void QobuzStreamURLRequest::GetStreamURL() {
   ++tries_;
 
   if (reply_) {
-    disconnect(reply_, 0, nullptr, 0);
+    disconnect(reply_, 0, this, 0);
     if (reply_->isRunning()) reply_->abort();
     reply_->deleteLater();
   }
@@ -147,7 +147,7 @@ void QobuzStreamURLRequest::GetStreamURL() {
 void QobuzStreamURLRequest::StreamURLReceived() {
 
   if (!reply_) return;
-  disconnect(reply_, 0, nullptr, 0);
+  disconnect(reply_, 0, this, 0);
   reply_->deleteLater();
 
   QByteArray data = GetReplyData(reply_);

src/subsonic/subsonicbaserequest.cpp

@@ -50,7 +50,7 @@ SubsonicBaseRequest::~SubsonicBaseRequest() {
 
   while (!replies_.isEmpty()) {
     QNetworkReply *reply = replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     if (reply->isRunning()) reply->abort();
     reply->deleteLater();
   }

src/subsonic/subsonicrequest.cpp

@@ -71,7 +71,7 @@ SubsonicRequest::~SubsonicRequest() {
 
   while (!album_cover_replies_.isEmpty()) {
     QNetworkReply *reply = album_cover_replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     if (reply->isRunning()) reply->abort();
     reply->deleteLater();
   }

src/subsonic/subsonicservice.cpp

@@ -95,7 +95,14 @@ SubsonicService::SubsonicService(Application *app, QObject *parent)
 }
 
 SubsonicService::~SubsonicService() {
-  collection_backend_->deleteLater();
+  delete collection_backend_;
+}
+
+void SubsonicService::Exit() {
+
+  connect(collection_backend_, SIGNAL(ExitFinished()), this, SIGNAL(ExitFinished()));
+  collection_backend_->ExitAsync();
+
 }
 
 void SubsonicService::ShowConfig() {
@@ -317,8 +324,8 @@ void SubsonicService::CheckConfiguration() {
 
 void SubsonicService::ResetSongsRequest() {
 
-  if (songs_request_.get()) {
+  if (songs_request_.get()) {  // WARNING: Don't disconnect everything. NewClosure() relies on destroyed()!!!
-    disconnect(songs_request_.get(), 0, nullptr, 0);
+    disconnect(songs_request_.get(), 0, this, 0);
     disconnect(this, 0, songs_request_.get(), 0);
     songs_request_.reset();
   }

src/subsonic/subsonicservice.h

@@ -60,6 +60,7 @@ class SubsonicService : public InternetService {
   static const Song::Source kSource;
 
   void ReloadSettings();
+  void Exit();
 
   Application *app() { return app_; }
 

src/tidal/tidalbaserequest.cpp

@@ -52,7 +52,7 @@ TidalBaseRequest::~TidalBaseRequest() {
 
   while (!replies_.isEmpty()) {
     QNetworkReply *reply = replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     if (reply->isRunning()) reply->abort();
     reply->deleteLater();
   }

src/tidal/tidalfavoriterequest.cpp

@@ -50,7 +50,7 @@ TidalFavoriteRequest::~TidalFavoriteRequest() {
 
   while (!replies_.isEmpty()) {
     QNetworkReply *reply = replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     reply->abort();
     reply->deleteLater();
   }

src/tidal/tidalrequest.cpp

@@ -80,7 +80,7 @@ TidalRequest::~TidalRequest() {
 
   while (!album_cover_replies_.isEmpty()) {
     QNetworkReply *reply = album_cover_replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     if (reply->isRunning()) reply->abort();
     reply->deleteLater();
   }

src/tidal/tidalservice.cpp

@@ -182,13 +182,35 @@ TidalService::~TidalService() {
 
   while (!stream_url_requests_.isEmpty()) {
     TidalStreamURLRequest *stream_url_req = stream_url_requests_.takeFirst();
-    disconnect(stream_url_req, 0, nullptr, 0);
+    disconnect(stream_url_req, 0, this, 0);
     stream_url_req->deleteLater();
   }
 
-  artists_collection_backend_->deleteLater();
+  delete artists_collection_backend_;
-  albums_collection_backend_->deleteLater();
+  delete albums_collection_backend_;
-  songs_collection_backend_->deleteLater();
+  delete songs_collection_backend_;
+
+}
+
+void TidalService::Exit() {
+
+  wait_for_exit_ << artists_collection_backend_ << albums_collection_backend_ << songs_collection_backend_;
+
+  connect(artists_collection_backend_, SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  connect(albums_collection_backend_, SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+  connect(songs_collection_backend_, SIGNAL(ExitFinished()), this, SLOT(ExitReceived()));
+
+  artists_collection_backend_->ExitAsync();
+  albums_collection_backend_->ExitAsync();
+  songs_collection_backend_->ExitAsync();
+
+}
+
+void TidalService::ExitReceived() {
+
+  disconnect(sender(), 0, this, 0);
+  wait_for_exit_.removeAll(sender());
+  if (wait_for_exit_.isEmpty()) emit ExitFinished();
 
 }
 
@@ -639,7 +661,7 @@ void TidalService::TryLogin() {
 void TidalService::ResetArtistsRequest() {
 
   if (artists_request_.get()) {
-    disconnect(artists_request_.get(), 0, nullptr, 0);
+    disconnect(artists_request_.get(), 0, this, 0);
     disconnect(this, 0, artists_request_.get(), 0);
     artists_request_.reset();
   }
@@ -694,7 +716,7 @@ void TidalService::ArtistsUpdateProgressReceived(const int id, const int progres
 void TidalService::ResetAlbumsRequest() {
 
   if (albums_request_.get()) {
-    disconnect(albums_request_.get(), 0, nullptr, 0);
+    disconnect(albums_request_.get(), 0, this, 0);
     disconnect(this, 0, albums_request_.get(), 0);
     albums_request_.reset();
   }
@@ -747,7 +769,7 @@ void TidalService::AlbumsUpdateProgressReceived(const int id, const int progress
 void TidalService::ResetSongsRequest() {
 
   if (songs_request_.get()) {
-    disconnect(songs_request_.get(), 0, nullptr, 0);
+    disconnect(songs_request_.get(), 0, this, 0);
     disconnect(this, 0, songs_request_.get(), 0);
     songs_request_.reset();
   }

src/tidal/tidalservice.h

@@ -61,6 +61,7 @@ class TidalService : public InternetService {
 
   static const Song::Source kSource;
 
+  void Exit();
   void ReloadSettings();
 
   void Logout();
@@ -132,6 +133,7 @@ class TidalService : public InternetService {
   void ResetSongsRequest();
 
  private slots:
+  void ExitReceived();
   void StartAuthorisation();
   void AuthorisationUrlReceived(const QUrl &url);
   void HandleLoginSSLErrors(QList<QSslError> ssl_errors);
@@ -245,6 +247,8 @@ class TidalService : public InternetService {
 
   QStringList login_errors_;
 
+  QList<QObject*> wait_for_exit_;
+
 };
 
 #endif  // TIDALSERVICE_H

src/tidal/tidalstreamurlrequest.cpp

@@ -52,7 +52,7 @@ TidalStreamURLRequest::TidalStreamURLRequest(TidalService *service, NetworkAcces
 TidalStreamURLRequest::~TidalStreamURLRequest() {
 
   if (reply_) {
-    disconnect(reply_, 0, nullptr, 0);
+    disconnect(reply_, 0, this, 0);
     if (reply_->isRunning()) reply_->abort();
     reply_->deleteLater();
   }
@@ -109,7 +109,7 @@ void TidalStreamURLRequest::GetStreamURL() {
   ++tries_;
 
   if (reply_) {
-    disconnect(reply_, 0, nullptr, 0);
+    disconnect(reply_, 0, this, 0);
     if (reply_->isRunning()) reply_->abort();
     reply_->deleteLater();
   }
@@ -144,7 +144,7 @@ void TidalStreamURLRequest::GetStreamURL() {
 void TidalStreamURLRequest::StreamURLReceived() {
 
   if (!reply_) return;
-  disconnect(reply_, 0, nullptr, 0);
+  disconnect(reply_, 0, this, 0);
   reply_->deleteLater();
 
   QByteArray data = GetReplyData(reply_, true);