use Qt signals to pass interpreter callbacks to octave-qobject * interpreter-qobject.h, interpreter-qobject.cc (interpreter_qobject::m_interpreter): New data member. (interpreter_qobject::execute): Cache pointer to interpreter after it is created. Set it to nullptr before exiting to disable interpreter events. (interpreter_qobject::interpreter_event): New functions. * octave-qobject.h, octave-qobject.cc (octave_qapplication::interpreter_event): New signals. (base_qobject::interpreter_event): New slots. Forward action to m_interpreter object interpreter_event functions. (base_qobject::base_qobject): Connect interpreter_event signals for octave_qapplication to the base_qobject::interpreter_event slots. (octave_qapplication::notify): Emit interpreter_event signal instead of using event_manager::post_exception. * qt-interpreter-events.cc: Declare and register octave::fcn_callback and octave::meth_callback as Qt meta types. * event-manager.h, event-manager.cc (event_manager::m_interpreter): New data member. Update constructor, change all uses. (octave::fcn_callback, octave::meth_callback): New typedefs. (event_manager::post_event): Limit allowable callback function signatures. For meth_callback functions, arrange for a reference to the interpreter object to be passed as the first argument. (event_manager::post_exception): Delete. (event_manager::rethrow_exception_callback): Delete. * GLCanvas.cc (GLCanvas::do_print): Use event_manager::post_event instead of event_manager::post_exception. * file-editor-tab.h (file_eitor_tab::interpreter_event): New signals. * file-editor.cc (file_editor::add_file_editor_tab): Forward interpreter_event signal from newly constructed file_editor_tab object to the interpreter_event signal of the file_editor object. * main-window.h, main-window.cc (main_window::construct): Connect the interpreter_event signal from the main_window object to the parent octave_qobject object. (main_window::interpreter_event): New signals. * octave-dock-widget.h, octave-dock-widget.cc (octave_dock_widget::octave_dock_widget) Forward the interpreter_event signal from the octave_dock_widget object to the interpreter_event signal for parent main_window object. (octave_dock_widget::interpreter_event): New signals. * variable-editor-model.h, variable-editor-model.cc (variable_editor_model::init_from_oct, variable_editor_model::retrieve_variable): Accept reference to interpreter object as an argument. Change all uses. (variable_editor_model::interpreter_event): New signals. * variable-editor.cc (variable_editor::edit_variable): Forward interpreter_event signal from newly constructed variable_editor_model to interpreter_event signal fro variable_editor object. * files-dock-widget.cc, file-editor-tab.cc, main-window.cc, variable-editor-model.cc: In all functions that need to perform interpreter actions, emit an interpreter_event signal instead of accessing the interprter event_manager and calling post_interpreter_event directly.

--- a/libinterp/corefcn/interpreter.cc	Sun Jul 28 17:24:42 2019 -0400
+++ b/libinterp/corefcn/interpreter.cc	Mon Jul 29 10:43:04 2019 -0400
@@ -381,7 +381,7 @@
       m_url_handle_manager (),
       m_cdef_manager (*this),
       m_gtk_manager (),
-      m_event_manager (),
+      m_event_manager (*this),
       m_interactive (false),
       m_read_site_files (true),
       m_read_init_files (m_app_context != nullptr),