Separate updating and networking code

Author: Quentin Peter

ipykernel/kernelbase.py

@@ -31,7 +31,7 @@
 from traitlets.config.configurable import SingletonConfigurable
 from IPython.core.error import StdinNotImplementedError, UsageError
 from ipython_genutils import py3compat
-from ipython_genutils.py3compat import unicode_type, string_types
+from ipython_genutils.py3compat import unicode_type, string_types, PY3
 from ipykernel.jsonutil import json_clean
 from traitlets import (
     Any, Instance, Float, Dict, List, Set, Integer, Unicode, Bool,
@@ -920,8 +920,8 @@ def _input_request(self, prompt, ident, parent, password=False):
             self._stdin_msg = None
             # Send the input request.
             content = json_clean(dict(prompt=prompt, password=password))
-            self.session.send(self.stdin_socket, u'input_request', content, parent,
-                              ident=ident)
+            self.session.send(self.stdin_socket, u'input_request',
+                              content, parent, ident=ident)
             # Await a response.
             reply = self._wait_input_request_reply()
 
@@ -943,32 +943,41 @@ def _wait_input_request_reply(self):
         KeyboardInterrupt if a keyboard interrupt is recieved.
         """
         # Await a response.
-        reply = None
-        while reply is None:
+        while True:
             try:
-                reply = self._input_request_loop_step()
+                # Try a non blocking recv
+                ident, reply = self.session.recv(
+                    self.stdin_socket, zmq.NOBLOCK)
+                if reply:
+                    return reply
+                if not self._input_request_loop_step():
+                    # Wait until a reply is recieved
+                    ident, reply = self.session.recv(self.stdin_socket, 0)
+                    return reply
             except Exception:
                 self.log.warning("Invalid Message:", exc_info=True)
             except KeyboardInterrupt:
                 # re-raise KeyboardInterrupt, to truncate traceback
                 raise KeyboardInterrupt
-        return reply
 
     def _input_request_loop_step(self):
-        """Do one step of the input request loop."""
+        """
+        Do one step of the input request loop.
+
+        Returns False if no additional steps are needed, otherwise True.
+        """
         # Allow GUI event loop to update
-        if sys.version_info >= (3, 4):
-            is_main_thread = (threading.current_thread() is
-                              threading.main_thread())
+        if PY3:
+            is_main_thread = (
+                threading.current_thread() is threading.main_thread())
         else:
-            is_main_thread = isinstance(threading.current_thread(),
-                                        threading._MainThread)
+            is_main_thread = isinstance(
+                threading.current_thread(), threading._MainThread)
         if is_main_thread and self.eventloop and self._input_eventloop:
             self.eventloop(self)
-            return self._stdin_msg
-        else:
-            ident, reply = self.session.recv(self.stdin_socket, 0)
-            return reply
+            return True
+        # No more steps are needed
+        return False
 
     def _at_shutdown(self):
         """Actions taken at shutdown by the kernel, called by python's atexit.