Restructure shutdown flow and behavior for improved robustness * file-editor-interface.h (file_editor_interface::check_closing): Remove closing_state argument from input. * file-editor-tab.cc (file_editor_tab::_cancelled): New static variable for managing chain of file closes. (file_editor_tab::file_editor_tab): Discard _app_closing and _modal_dialog initializations. (file_editor_tab::closeEvent): Upon accepting the close event, als request tab removal. (file_editor_tab::check_modified_file): New simple routine checking for modified file if there hasn't been cancellation yet. (file_editor_tab::run_file): Remove use of _modal_dialog. (file_editor_tab::show_dialog): Add modal input setting. Remove use of _app_closing and _modal_dialog. (file_editor_tab::check_file_modified): Remove situational message for just one. If modified, call show_dialog with modal true, return QMessageBox::Cancel if anything cancelled, otherwise the user decision. (file_editor_tab::handle_file_modified_answer): Do not remove file editor tab in any case. If user cancelled, set _cancelled true. (file_editor_tab::save_file): Add "false" (non-modal) to show_dialog() call. (file_editor_tab::save_file_as): Add "false" (non-modal) to show_dialog() call. (file_editor_tab::conditional_close): Remove input argument and use of variable _app_closing. * file-editor-tab.h (file_editor_tab::conditional_close): Remove input argument. (file_editor_tab::reset_cancel): New member function declaration for managing cancellation of tab chain saves. (file_editor_tab::was_cancel): New member function for indicating any cancellation when saving modified files. (file_editor_tab::check_modified_file): New slot declaration for checking and saving file modifications. (file_editor_tab::show_dialog): Add modal option input argument. (file_editor_tab::_app_closing, file_editor_tab::_modal_dialog): Remove. (file_editor_tab::_cancelled): Add. * file-editor.cc (file_editor::file_editor): Remove _check_closing_done initialization. (file_editor::~file_editor): Remove use of _check_closing_done and check_closing(). (file_editor::check_closing): Clear cancellation history and check all files for modifications, without closing. Close all tabs and delete associated widgets if no cancellation. Remove use of _check_closing_done. (file_editor::request_close_file): Remove argument from conditional_close() function call. (file_editor::request_close_all_files): Ditto. (file_editor::request_close_other_files): Ditto. (file_editor::handle_tab_close_request): Ditto. (file_editor::handle_tab_remove_request): Add comment about deleting sender. (file_editor::add_file_editor_tab): Connect fetab_check_modified_file signal to check_modified_file slot. * file-editor.h (file_editor::fetab_check_modified_file): New signal. (file_editor::check_closing): Remove input argument. (file_editor::_check_closing_done): Remove. * main-window.cc (main_window::confirm_shutdown_octave): Rename of member function main_window::confirm_exit_octave(). Change return type to void. Set octave/qt link confirmation result then awake worker process. (main_window::exit_app): Rename of member function main_window::exit(). (main_window::closeEvent): Rather than post callback event, queue "exit" in the command buffer. (main_window::construct_octave_qt_link): Connect confirm_shutdown_signal to confirm_shutdown_octave slot. Connect exit_app_signal to exit_app slot. (main_window::exit_callback): Remove. (main_window::confirm_exit_octave): Renamed as confirm_shutdown_octave(). * main-window.h (main_window::confirm_shutdown_octave): Rename of slot confirm_exit_octave(). (main_window::exit): Renamed exit_app(). (main_window::exit_callback): Removed declaration. (main_window::confirm_exit_octave): Renamed confirm_shutdown_octave(). * octave-qt-link.cc (octave_qt_link::do_confirm_shutdown): New virtual function definition for initiating GUI shutdown and confirm exit. Worker process goes into sleep mode after issuing cross-thread signal. Return confirmation result. (octave_qt_link::do_exit): Change exit_signal to exit_app_signal. octave-qt-link.h (octave_qt_link::do_confirm_shutdown): New virtual function declaration for qt GUI. (octave_qt_link::mutex): Added. A QMutex for communicating with Qt GUI. (octave_qt_link::waitcondition): Added. For process wait. (octave_qt_link::shutdown_confirmation): Added. Store confirmation result. (octave_qt_link::_shutdown_confirm_result): Added. Confirmation result. (octave_qt_link::exit_signal): Signal renamed exit_app_signal. (octave_qt_link::confirm_shutdown_signal): Added. (octave_qt_link::exit_app_signal): Renamed of exit_signal. octave-link.h (octave_link::confirm_shutdown): Added. Access virtual function do_confirm_shutdown. (octave_link::do_confirm_shutdown): Added. Virtual function for GUI link. toplev.cc (clean_up_and_exit): Change 'retval' to 'status', as header file uses argument name 'status'. (quit): First initiate GUI shutdown via octave_link::confirm_shutdown() and if not confirmed, immediately return thereby avoiding exit sequence.

--- a/libgui/src/main-window.cc
+++ b/libgui/src/main-window.cc
@@ -777,6 +777,33 @@
   resource_manager::update_network_settings ();
 }
 
+void
+main_window::confirm_shutdown_octave (void)
+{
+  bool closenow = true;
+
+  QSettings *settings = resource_manager::get_settings ();
+
+  if (settings->value ("prompt_to_exit", false).toBool ())
+    {
+      int ans = QMessageBox::question (this, tr ("Octave"),
+         tr ("Are you sure you want to exit Octave?"),
+          QMessageBox::Ok | QMessageBox::Cancel, QMessageBox::Ok);
+
+      if (ans !=  QMessageBox::Ok)
+        closenow = false;
+    }
+
+#ifdef HAVE_QSCINTILLA
+  if (closenow)
+    closenow = editor_window->check_closing ();
+#endif
+
+  _octave_qt_link->shutdown_confirmation (closenow);
+
+  // Awake the worker thread so that it continues shutting down (or not).
+  _octave_qt_link->waitcondition.wakeAll ();
+}
 
 void
 main_window::prepare_to_exit (void)
@@ -785,7 +812,7 @@
 }
 
 void
-main_window::exit (int status)
+main_window::exit_app (int status)
 {
   qApp->exit (status);
 }
@@ -985,8 +1012,7 @@
 main_window::closeEvent (QCloseEvent *e)
 {
   e->ignore ();
-  if (confirm_exit_octave())
-    octave_link::post_event (this, &main_window::exit_callback);
+  queue_command ("exit");
 }
 
 void
@@ -1435,8 +1461,11 @@
 {
   _octave_qt_link = new octave_qt_link (this);
 
-  connect (_octave_qt_link, SIGNAL (exit_signal (int)),
-           this, SLOT (exit (int)));
+  connect (_octave_qt_link, SIGNAL (confirm_shutdown_signal ()),
+           this, SLOT (confirm_shutdown_octave ()));
+
+  connect (_octave_qt_link, SIGNAL (exit_app_signal (int)),
+           this, SLOT (exit_app (int)));
 
   connect (_octave_qt_link,
            SIGNAL (set_workspace_signal
@@ -2138,12 +2167,6 @@
 }
 
 void
-main_window::exit_callback (void)
-{
-  Fquit ();
-}
-
-void
 main_window::find_files (const QString &start_dir)
 {
 
@@ -2358,29 +2381,3 @@
   _clipboard->clear (QClipboard::Clipboard);
 }
 
-bool
-main_window::confirm_exit_octave ()
-{
-  bool closenow = true;
-
-  QSettings *settings = resource_manager::get_settings ();
-
-  if (settings->value ("prompt_to_exit", false).toBool ())
-    {
-      int ans = QMessageBox::question (this, tr ("Octave"),
-         tr ("Are you sure you want to exit Octave?"),
-          QMessageBox::Ok | QMessageBox::Cancel, QMessageBox::Ok);
-
-      if (ans !=  QMessageBox::Ok)
-        return false;
-
-    }
-
-#ifdef HAVE_QSCINTILLA
-  closenow = editor_window->check_closing (1);  // 1: exit request from gui
-#endif
-
-  return closenow;
-}
-
-