From 953eb4b1457ba2384ba6b8daf480292a5acacca8 Mon Sep 17 00:00:00 2001
From: RK <rollokb+github@gmail.com>
Date: Mon, 1 Feb 2021 09:44:10 +0000
Subject: [PATCH] Issue #12786: Create hook for dispatching messages out of
 order

---
 ipykernel/inprocess/client.py |  4 +---
 ipykernel/kernelbase.py       | 37 ++++++++++++++++++++++++++---------
 2 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/ipykernel/inprocess/client.py b/ipykernel/inprocess/client.py
index 1784a6eaa..f424eedee 100644
--- a/ipykernel/inprocess/client.py
+++ b/ipykernel/inprocess/client.py
@@ -173,10 +173,8 @@ def _dispatch_to_kernel(self, msg):
             raise RuntimeError('Cannot send request. No kernel exists.')
 
         stream = kernel.shell_stream
-        self.session.send(stream, msg)
-        msg_parts = stream.recv_multipart()
         loop = asyncio.get_event_loop()
-        loop.run_until_complete(kernel.dispatch_shell(msg_parts))
+        loop.run_until_complete(kernel.dispatch_shell(msg))
         idents, reply_msg = self.session.recv(stream, copy=False)
         self.shell_channel.call_handlers_later(reply_msg)
 
diff --git a/ipykernel/kernelbase.py b/ipykernel/kernelbase.py
index e391411e4..36f15f5a4 100644
--- a/ipykernel/kernelbase.py
+++ b/ipykernel/kernelbase.py
@@ -306,12 +306,8 @@ async def dispatch_shell(self, msg):
         # flush control queue before handling shell requests
         await self._flush_control_queue()
 
-        idents, msg = self.session.feed_identities(msg, copy=False)
-        try:
-            msg = self.session.deserialize(msg, content=True, copy=False)
-        except Exception:
-            self.log.error("Invalid Message", exc_info=True)
-            return
+        if idents is None:
+            idents = []
 
         # Set the parent message for side effects.
         self.set_parent(idents, msg, channel='shell')
@@ -465,15 +461,38 @@ async def dispatch_queue(self):
     def _message_counter_default(self):
         return itertools.count()
 
-    def schedule_dispatch(self, dispatch, *args):
+    def should_dispatch_immediately(self, msg):
+        """
+        This provides a hook for dispatching incoming messages
+        from the frontend immediately, and out of order.
+
+        It could be used to allow asynchronous messages from
+        GUIs to be processed.
+        """
+        return False
+
+    def schedule_dispatch(self, msg, dispatch):
         """schedule a message for dispatch"""
+
+        idents, msg = self.session.feed_identities(msg, copy=False)
+        try:
+            msg = self.session.deserialize(msg, content=True, copy=False)
+        except:
+            self.log.error("Invalid shell message", exc_info=True)
+            return
+
+        new_args = (msg, idents)
+
+        if self.should_dispatch_immediately(msg):
+            return self.io_loop.add_callback(dispatch, *new_args)
+
         idx = next(self._message_counter)
 
         self.msg_queue.put_nowait(
             (
                 idx,
                 dispatch,
-                args,
+                new_args,
             )
         )
         # ensure the eventloop wakes up
@@ -497,7 +516,7 @@ def start(self):
         self.shell_stream.on_recv(
             partial(
                 self.schedule_dispatch,
-                self.dispatch_shell,
+                dispatch=self.dispatch_shell,
             ),
             copy=False,
         )