From e9301c9b52a1ebd4f72527098da896097f46c5fa 2016-07-06 10:20:00
From: Thomas Kluyver <thomas@kluyver.me.uk>
Date: 2016-07-06 10:20:00
Subject: [PATCH] Try to fix Qt event loop, take III

This involves neither threads nor calling in to the old inputhook
machinery.

---

diff --git a/IPython/terminal/pt_inputhooks/qt.py b/IPython/terminal/pt_inputhooks/qt.py
index 1fd4e92..ebf3a94 100644
--- a/IPython/terminal/pt_inputhooks/qt.py
+++ b/IPython/terminal/pt_inputhooks/qt.py
@@ -1,3 +1,4 @@
+import sys
 from IPython.external.qt_for_kernel import QtCore, QtGui
 
 def inputhook(context):
@@ -5,7 +6,20 @@ def inputhook(context):
     if not app:
         return
     event_loop = QtCore.QEventLoop(app)
-    notifier = QtCore.QSocketNotifier(context.fileno(), QtCore.QSocketNotifier.Read)
-    notifier.setEnabled(True)
-    notifier.activated.connect(event_loop.exit)
-    event_loop.exec_()
+
+    if sys.platform == 'win32':
+        # The QSocketNotifier method doesn't appear to work on Windows.
+        # Use polling instead.
+        timer = QtCore.QTimer()
+        timer.timeout.connect(event_loop.quit)
+        while not context.input_is_ready():
+            timer.start(50)  # 50 ms
+            event_loop.exec_()
+            timer.stop()
+    else:
+        # On POSIX platforms, we can use a file descriptor to quit the event
+        # loop when there is input ready to read.
+        notifier = QtCore.QSocketNotifier(context.fileno(), QtCore.QSocketNotifier.Read)
+        notifier.setEnabled(True)
+        notifier.activated.connect(event_loop.exit)
+        event_loop.exec_()