Backport PR matplotlib#30209: Clean up Qt socket notifier to avoid spurious interrupt handler calls

Author: anntzer

lib/matplotlib/backend_bases.py

@@ -1616,7 +1616,8 @@ def _allow_interrupt(prepare_notifier, handle_sigint):
     If SIGINT was indeed caught, after exiting the on_signal() function the
     interpreter reacts to the signal according to the handler function which
     had been set up by a signal.signal() call; here, we arrange to call the
-    backend-specific *handle_sigint* function.  Finally, we call the old SIGINT
+    backend-specific *handle_sigint* function, passing the notifier object
+    as returned by prepare_notifier().  Finally, we call the old SIGINT
     handler with the same arguments that were given to our custom handler.
 
     We do this only if the old handler for SIGINT was not None, which means
@@ -1626,7 +1627,7 @@ def _allow_interrupt(prepare_notifier, handle_sigint):
     Parameters
     ----------
     prepare_notifier : Callable[[socket.socket], object]
-    handle_sigint : Callable[[], object]
+    handle_sigint : Callable[[object], object]
     """
 
     old_sigint_handler = signal.getsignal(signal.SIGINT)
@@ -1642,9 +1643,10 @@ def _allow_interrupt(prepare_notifier, handle_sigint):
     notifier = prepare_notifier(rsock)
 
     def save_args_and_handle_sigint(*args):
-        nonlocal handler_args
+        nonlocal handler_args, notifier
         handler_args = args
-        handle_sigint()
+        handle_sigint(notifier)
+        notifier = None
 
     signal.signal(signal.SIGINT, save_args_and_handle_sigint)
     try:

lib/matplotlib/backends/backend_qt.py

@@ -169,9 +169,14 @@ def _may_clear_sock():
                 # be forgiving about reading an empty socket.
                 pass
 
-        return sn  # Actually keep the notifier alive.
-
-    def handle_sigint():
+        # We return the QSocketNotifier so that the caller holds a reference, and we
+        # also explicitly clean it up in handle_sigint(). Without doing both, deletion
+        # of the socket notifier can happen prematurely or not at all.
+        return sn
+
+    def handle_sigint(sn):
+        sn.deleteLater()
+        QtCore.QCoreApplication.sendPostedEvents(sn, QtCore.QEvent.Type.DeferredDelete)
         if hasattr(qapp_or_eventloop, 'closeAllWindows'):
             qapp_or_eventloop.closeAllWindows()
         qapp_or_eventloop.quit()

src/_macosx.m

@@ -258,7 +258,7 @@ static void lazy_init(void) {
 }
 
 static PyObject*
-stop(PyObject* self)
+stop(PyObject* self, PyObject* _ /* ignored */)
 {
     stopWithEvent();
     Py_RETURN_NONE;
@@ -1863,7 +1863,7 @@ - (void)flagsChanged:(NSEvent *)event
             "written on the file descriptor given as argument.")},
         {"stop",
          (PyCFunction)stop,
-         METH_NOARGS,
+         METH_VARARGS,
          PyDoc_STR("Stop the NSApp.")},
         {"show",
          (PyCFunction)show,