Turn off parallel SQL updates for MySQL.

src/core/feeddownloader.cpp

@@ -41,7 +41,7 @@ bool FeedDownloader::isUpdateRunning() const {
 }
 
 void FeedDownloader::updateFeeds(const QList<Feed*> &feeds) {
-  qDebug().nospace() << "Performing feed updates in thread: \'" << QThread::currentThreadId() << "\'.";
+  qDebug().nospace() << "Starting feed updates from worker in thread: \'" << QThread::currentThreadId() << "\'.";
 
   // It may be good to disable "stop" action when batch feed update
   // starts.

src/miscellaneous/application.cpp

@@ -40,7 +40,7 @@
 
 Application::Application(const QString &id, int &argc, char **argv)
   : QtSingleApplication(id, argc, argv),
-    m_updateFeedsLock(NULL), m_feedServices(QList<ServiceEntryPoint*>()), m_userActions(QList<QAction*>()), m_mainForm(NULL),
+    m_updateFeedsLock(NULL), m_updateMessagesLock(NULL), m_feedServices(QList<ServiceEntryPoint*>()), m_userActions(QList<QAction*>()), m_mainForm(NULL),
     m_trayIcon(NULL), m_settings(NULL), m_system(NULL), m_skins(NULL),
     m_localization(NULL), m_icons(NULL), m_database(NULL), m_downloadManager(NULL) {
   connect(this, SIGNAL(aboutToQuit()), this, SLOT(onAboutToQuit()));
@@ -123,6 +123,16 @@ Mutex *Application::feedUpdateLock() {
   return m_updateFeedsLock.data();
 }
 
+Mutex *Application::messageUpdateLock() {
+  if (m_updateMessagesLock.isNull()) {
+    // NOTE: Cannot use parent hierarchy because this method can be usually called
+    // from any thread.
+    m_updateMessagesLock.reset(new Mutex());
+  }
+
+  return m_updateMessagesLock.data();
+}
+
 void Application::backupDatabaseSettings(bool backup_database, bool backup_settings,
                                          const QString &target_path, const QString &backup_name) {
   if (!QFileInfo(target_path).isWritable()) {

src/miscellaneous/application.h

@@ -112,6 +112,7 @@ class Application : public QtSingleApplication {
 
     // Access to application-wide close lock.
     Mutex *feedUpdateLock();
+    Mutex *messageUpdateLock();
 
     inline FormMain *mainForm() {
       return m_mainForm;
@@ -184,6 +185,8 @@ class Application : public QtSingleApplication {
     // tries to lock the lock for writing), then no other
     // action will be allowed to lock for reading.
     QScopedPointer<Mutex> m_updateFeedsLock;
+    QScopedPointer<Mutex> m_updateMessagesLock;
+
     QList<ServiceEntryPoint*> m_feedServices;
     QList<QAction*> m_userActions;
     FormMain *m_mainForm;

src/services/abstract/feed.cpp

@@ -19,10 +19,13 @@
 
 #include "definitions/definitions.h"
 #include "miscellaneous/application.h"
+#include "miscellaneous/mutex.h"
 #include "miscellaneous/databasequeries.h"
 #include "services/abstract/recyclebin.h"
 #include "services/abstract/serviceroot.h"
 
+#include <QThread>
+
 
 Feed::Feed(RootItem *parent)
   : RootItem(parent), m_url(QString()), m_status(Normal), m_autoUpdateType(DefaultAutoUpdate),
@@ -131,6 +134,8 @@ void Feed::updateCounts(bool including_total_count) {
 }
 
 void Feed::run() {
+  qDebug().nospace() << "Updating feed " << customId() << " in thread: \'" << QThread::currentThreadId() << "\'.";
+
   emit updated(update());
 }
 
@@ -139,6 +144,13 @@ int Feed::updateMessages(const QList<Message> &messages) {
   int account_id = getParentServiceRoot()->accountId();
   bool anything_updated = false;
   bool ok;
+
+  // MySQL seems to be more error prone with transactions when called
+  // from more threads in the same time. SQLite does not have that limitation.
+  if (qApp->database()->activeDatabaseDriver() == DatabaseFactory::MYSQL) {
+    qApp->messageUpdateLock()->lock();
+  }
+
   QSqlDatabase database = qApp->database()->connection(metaObject()->className(), DatabaseFactory::FromSettings);
   int updated_messages = DatabaseQueries::updateMessages(database, messages, custom_id, account_id, url(),
                                                          &anything_updated, &ok);
@@ -164,5 +176,9 @@ int Feed::updateMessages(const QList<Message> &messages) {
     getParentServiceRoot()->itemChanged(items_to_update);
   }
 
+  if (qApp->database()->activeDatabaseDriver() == DatabaseFactory::MYSQL) {
+    qApp->messageUpdateLock()->unlock();
+  }
+
   return updated_messages;
 }