Fix thread unsafe simulator shutdown. Use a signal/slot connection to execute on correct thread

src/comm/QGCFlightGearLink.cc

@@ -70,6 +70,7 @@ QGCFlightGearLink::QGCFlightGearLink(UASInterface* mav, QString startupArguments
     
     // We need a mechanism so show error message from our FGLink thread on the UI thread. This signal connection will do that for us.
     connect(this, &QGCFlightGearLink::showCriticalMessageFromThread, qgcApp(), &QGCApplication::criticalMessageBoxOnMainThread);
+    connect(this, &QGCFlightGearLink::disconnectSim, this, &QGCFlightGearLink::disconnectSimulation);
 }
 
 QGCFlightGearLink::~QGCFlightGearLink()
@@ -496,13 +497,13 @@ bool QGCFlightGearLink::disconnectSimulation()
     if (_fgProcess)
     {
         _fgProcess->close();
-        delete _fgProcess;
+        _fgProcess->deleteLater();
         _fgProcess = NULL;
     }
     if (_udpCommSocket)
     {
         _udpCommSocket->close();
-        delete _udpCommSocket;
+        _udpCommSocket->deleteLater();
         _udpCommSocket = NULL;
     }
 

src/comm/QGCHilLink.h

@@ -83,6 +83,11 @@ signals:
      **/
     void simulationDisconnected();
 
+    /**
+     * @brief Thread safe signal to disconnect simulator from other threads
+     **/
+    void disconnectSim();
+
     /**
      * @brief This signal is emitted instantly when the link status changes
      **/

src/uas/UAS.cc

@@ -3227,7 +3227,7 @@ void UAS::startHil()
 void UAS::stopHil()
 {
     if (simulation && simulation->isConnected()) {
-        simulation->disconnectSimulation();
+        simulation->disconnectSim();
         setMode(base_mode & ~MAV_MODE_FLAG_HIL_ENABLED, custom_mode);
         qDebug() << __FILE__ << __LINE__ << "HIL is onboard not enabled, trying to disable.";
     }