fix: there can be only one comm_manager

ipykernel/ipkernel.py

@@ -5,6 +5,7 @@
 import getpass
 import signal
 import sys
+import threading
 import typing as t
 from contextlib import contextmanager
 from functools import partial
@@ -46,9 +47,19 @@ def _create_comm(*args, **kwargs):
     return BaseComm(*args, **kwargs)
 
 
+# there can only be one comm manager in a ipykernel process
+lock = threading.Lock()
+comm_manager : t.Optional[CommManager] = None
+
+
 def _get_comm_manager(*args, **kwargs):
     """Create a new CommManager."""
-    return CommManager(*args, **kwargs)
+    global comm_manager
+    if comm_manager is None:
+        with lock:
+            if comm_manager is None:
+                comm_manager = CommManager(*args, **kwargs)
+    return comm_manager
 
 
 comm.create_comm = _create_comm

ipykernel/tests/test_comm.py

@@ -1,7 +1,13 @@
 from ipykernel.comm import Comm
-
+from .utils import kernel
+from ipykernel.ipkernel import IPythonKernel
 
 async def test_comm(kernel):
     c = Comm()
     c.kernel = kernel  # type:ignore
     c.publish_msg("foo")
+
+
+def test_comm_in_manager(ipkernel: IPythonKernel):
+    comm = Comm()
+    assert comm.comm_id in ipkernel.comm_manager.comms