Initiate saving state from main thread

This is architecturally more consistent, but also necessary for the
coming change of being able to reload bridges, to not get concurrent
access on the bridge configs.

mainapp.cpp

@@ -109,7 +109,7 @@ MainApp::MainApp(const std::string &configFilePath) :
         subscriptionStore->loadSessionsAndSubscriptions(settings.getSessionsDBFile());
     }
 
-    auto fSaveState = std::bind(&MainApp::saveStateInThread, this);
+    auto fSaveState = std::bind(&MainApp::queueSaveStateInThread, this);
     timer.addCallback(fSaveState, 900000, "Save state.");
 
     auto fSendPendingWills = std::bind(&MainApp::queueSendQueuedWills, this);
@@ -280,8 +280,18 @@ void MainApp::saveStateInThread()
 
     auto f = std::bind(&MainApp::saveState, this->settings, bridgeInfos, true);
     this->bgWorker.addTask(f);
+}
 
-
+/**
+ * @brief MainApp::queueSaveStateInThread is a wrapper to be called from another thread, to make sure saveStateInThread() is called
+ * on the main loop.
+ */
+void MainApp::queueSaveStateInThread()
+{
+    std::lock_guard<std::mutex> locker(eventMutex);
+    auto f = std::bind(&MainApp::saveStateInThread, this);
+    taskQueue.push_back(f);
+    wakeUpThread();
 }
 
 void MainApp::queueSendQueuedWills()

mainapp.h

@@ -88,6 +88,7 @@ class MainApp
     static void saveBridgeInfo(const std::string &filePath, const std::list<BridgeInfoForSerializing> &bridgeInfos);
     void loadBridgeInfo();
     void saveStateInThread();
+    void queueSaveStateInThread();
     void queueSendQueuedWills();
     void waitForWillsQueued();
     void waitForDisconnectsInitiated();