Insure canvas rendering jobs are cancelled when exiting QGIS

src/app/qgisapp.cpp

@@ -1362,8 +1362,6 @@ QgisApp::QgisApp()
 
 QgisApp::~QgisApp()
 {
-  stopRendering();
-
   delete mInternalClipboard;
   delete mQgisInterface;
   delete mStyleSheetBuilder;
@@ -1452,6 +1450,12 @@ QgisApp::~QgisApp()
   qDeleteAll( mCustomDropHandlers );
   qDeleteAll( mCustomLayoutDropHandlers );
 
+  const QList<QgsMapCanvas *> canvases = mapCanvases();
+  for ( QgsMapCanvas *canvas : canvases )
+  {
+    delete canvas;
+  }
+
   // This function *MUST* be the last one called, as it destroys in
   // particular GDAL. As above objects can hold GDAL/OGR objects, it is not
   // safe destroying them afterwards

src/gui/qgsmapcanvas.cpp

@@ -211,6 +211,16 @@ QgsMapCanvas::~QgsMapCanvas()
     delete mJob;
   }
 
+  QList< QgsMapRendererQImageJob * >::const_iterator previewJob = mPreviewJobs.constBegin();
+  for ( ; previewJob != mPreviewJobs.constEnd(); ++previewJob )
+  {
+    if ( *previewJob )
+    {
+      whileBlocking( *previewJob )->cancel();
+      delete *previewJob;
+    }
+  }
+
   // delete canvas items prior to deleting the canvas
   // because they might try to update canvas when it's
   // already being destructed, ends with segfault