Allow interrupting input() on Windows, as part of effort to make pdb interruptible

ipykernel/kernelbase.py

@@ -867,6 +867,7 @@ def _input_request(self, prompt, ident, parent, password=False):
         # Flush output before making the request.
         sys.stderr.flush()
         sys.stdout.flush()
+
         # flush the stdin socket, to purge stale replies
         while True:
             try:
@@ -885,14 +886,20 @@ def _input_request(self, prompt, ident, parent, password=False):
         # Await a response.
         while True:
             try:
-                ident, reply = self.session.recv(self.stdin_socket, 0)
-            except Exception:
+                ident, reply = self.session.recv(self.stdin_socket)
+            except Exception as e:
                 self.log.warning("Invalid Message:", exc_info=True)
             except KeyboardInterrupt:
                 # re-raise KeyboardInterrupt, to truncate traceback
                 raise KeyboardInterrupt("Interrupted by user") from None
             else:
-                break
+                # Use polling with sleep so KeyboardInterrupts can get through;
+                # doing a blocking recv() means stdin reads are uninterruptible
+                # on Windows:
+                if (ident, reply) == (None, None):
+                    time.sleep(0.001)
+                else:
+                    break
         try:
             value = py3compat.unicode_to_str(reply['content']['value'])
         except:

ipykernel/tests/test_kernel.py

@@ -330,3 +330,20 @@ def test_shutdown():
             else:
                 break
         assert not km.is_alive()
+
+
+def test_interrupt_during_input():
+    """The kernel exits after being interrupted, while waiting in input().
+
+    input() appears to have issues other functions don't, and it needs to be
+    interruptible in order for pdb to be interruptible.
+    """
+    with new_kernel() as kc:
+        km = kc.parent
+        msg_id = kc.execute("input()")
+        time.sleep(1)  # Make sure it's actually waiting for input.
+        km.interrupt_kernel()
+        # If we failed to interrupt interrupt, this will timeout:
+        reply = kc.get_shell_msg(timeout=TIMEOUT)
+        from .test_message_spec import validate_message
+        validate_message(reply, 'execute_reply', msg_id)