Merge pull request #2294 from bfroehle/inputhook_qt4_alt

inputhook_qt4: Use QEventLoop instead of starting up the QCoreApplication

IPython/lib/inputhookqt4.py

@@ -1,122 +1,144
 # -*- coding: utf-8 -*-
 """
 Qt4's inputhook support function
 
 Author: Christian Boos
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 from IPython.core.interactiveshell import InteractiveShell
 from IPython.external.qt_for_kernel import QtCore, QtGui
 from IPython.lib.inputhook import allow_CTRL_C, ignore_CTRL_C, stdin_ready
 
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
 def create_inputhook_qt4(mgr, app=None):
     """Create an input hook for running the Qt4 application event loop.
 
     Parameters
     ----------
     mgr : an InputHookManager
 
     app : Qt Application, optional.
         Running application to use.  If not given, we probe Qt for an
         existing application object, and create a new one if none is found.
 
     Returns
     -------
     A pair consisting of a Qt Application (either the one given or the
     one found or created) and a inputhook.
 
     Notes
     -----
     We use a custom input hook instead of PyQt4's default one, as it
     interacts better with the readline packages (issue #481).
 
     The inputhook function works in tandem with a 'pre_prompt_hook'
     which automatically restores the hook as an inputhook in case the
     latter has been temporarily disabled after having intercepted a
     KeyboardInterrupt.
     """
 
     if app is None:
         app = QtCore.QCoreApplication.instance()
         if app is None:
             app = QtGui.QApplication([" "])
 
     # Re-use previously created inputhook if any
     ip = InteractiveShell.instance()
     if hasattr(ip, '_inputhook_qt4'):
         return app, ip._inputhook_qt4
 
     # Otherwise create the inputhook_qt4/preprompthook_qt4 pair of
     # hooks (they both share the got_kbdint flag)
 
     got_kbdint = [False]
 
     def inputhook_qt4():
         """PyOS_InputHook python hook for Qt4.
 
         Process pending Qt events and if there's no pending keyboard
         input, spend a short slice of time (50ms) running the Qt event
         loop.
 
         As a Python ctypes callback can't raise an exception, we catch
         the KeyboardInterrupt and temporarily deactivate the hook,
         which will let a *second* CTRL+C be processed normally and go
         back to a clean prompt line.
         """
         try:
             allow_CTRL_C()
             app = QtCore.QCoreApplication.instance()
             if not app: # shouldn't happen, but safer if it happens anyway...
                 return 0
             app.processEvents(QtCore.QEventLoop.AllEvents, 300)
             if not stdin_ready():
+                # Generally a program would run QCoreApplication::exec()
+                # from main() to enter and process the Qt event loop until
+                # quit() or exit() is called and the program terminates.
+                #
+                # For our input hook integration, we need to repeatedly
+                # enter and process the Qt event loop for only a short
+                # amount of time (say 50ms) to ensure that Python stays
+                # responsive to other user inputs.
+                #
+                # A naive approach would be to repeatedly call
+                # QCoreApplication::exec(), using a timer to quit after a
+                # short amount of time. Unfortunately, QCoreApplication
+                # emits an aboutToQuit signal before stopping, which has
+                # the undesirable effect of closing all modal windows.
+                #
+                # To work around this problem, we instead create a
+                # QEventLoop and call QEventLoop::exec(). Other than
+                # setting some state variables which do not seem to be
+                # used anywhere, the only thing QCoreApplication adds is
+                # the aboutToQuit signal which is precisely what we are
+                # trying to avoid.
                 timer = QtCore.QTimer()
-                timer.timeout.connect(app.quit)
+                event_loop = QtCore.QEventLoop()
+                timer.timeout.connect(event_loop.quit)
                 while not stdin_ready():
                     timer.start(50)
-                    app.exec_()
+                    event_loop.exec_()
                     timer.stop()
         except KeyboardInterrupt:
             ignore_CTRL_C()
             got_kbdint[0] = True
             print("\nKeyboardInterrupt - Ctrl-C again for new prompt")
             mgr.clear_inputhook()
         except: # NO exceptions are allowed to escape from a ctypes callback
             ignore_CTRL_C()
             from traceback import print_exc
             print_exc()
             print("Got exception from inputhook_qt4, unregistering.")
             mgr.clear_inputhook()
         finally:
             allow_CTRL_C()
         return 0
 
     def preprompthook_qt4(ishell):
         """'pre_prompt_hook' used to restore the Qt4 input hook
 
         (in case the latter was temporarily deactivated after a
         CTRL+C)
         """
         if got_kbdint[0]:
             mgr.set_inputhook(inputhook_qt4)
         got_kbdint[0] = False
 
     ip._inputhook_qt4 = inputhook_qt4
     ip.set_hook('pre_prompt_hook', preprompthook_qt4)
 
     return app, inputhook_qt4