Support control<>iopub messages to e.g. unblock comm_msg from command execution

ipykernel/comm/comm.py

@@ -3,6 +3,7 @@
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
+import threading
 import uuid
 from typing import Optional
 from warnings import warn
@@ -11,6 +12,7 @@
 import traitlets.config
 from traitlets import Bool, Bytes, Instance, Unicode, default
 
+from ipykernel.control import CONTROL_THREAD_NAME
 from ipykernel.jsonutil import json_clean
 from ipykernel.kernelbase import Kernel
 
@@ -30,6 +32,11 @@ def publish_msg(self, msg_type, data=None, metadata=None, buffers=None, **keys):
         metadata = {} if metadata is None else metadata
         content = json_clean(dict(data=data, comm_id=self.comm_id, **keys))
 
+        if threading.current_thread().name == CONTROL_THREAD_NAME:
+            channel_from_which_to_get_parent_header = "control"
+        else:
+            channel_from_which_to_get_parent_header = "shell"
+
         if self.kernel is None:
             self.kernel = Kernel.instance()
 
@@ -38,7 +45,7 @@ def publish_msg(self, msg_type, data=None, metadata=None, buffers=None, **keys):
             msg_type,
             content,
             metadata=json_clean(metadata),
-            parent=self.kernel.get_parent("shell"),
+            parent=self.kernel.get_parent(channel_from_which_to_get_parent_header),
             ident=self.topic,
             buffers=buffers,
         )

ipykernel/control.py

@@ -3,20 +3,22 @@
 
 from tornado.ioloop import IOLoop
 
+CONTROL_THREAD_NAME = "Control"
+
 
 class ControlThread(Thread):
     """A thread for a control channel."""
 
     def __init__(self, **kwargs):
         """Initialize the thread."""
-        Thread.__init__(self, name="Control", **kwargs)
+        Thread.__init__(self, name=CONTROL_THREAD_NAME, **kwargs)
         self.io_loop = IOLoop(make_current=False)
         self.pydev_do_not_trace = True
         self.is_pydev_daemon_thread = True
 
     def run(self):
         """Run the thread."""
-        self.name = "Control"
+        self.name = CONTROL_THREAD_NAME
         try:
             self.io_loop.start()
         finally: