Make kernelbase._eventloop_set event thread-safe

Author: davidbrochart

ipykernel/kernelapp.py

@@ -20,7 +20,7 @@
 
 import zmq
 import zmq.asyncio
-from anyio import create_task_group, run
+from anyio import create_task_group, run, to_thread
 from IPython.core.application import (  # type:ignore[attr-defined]
     BaseIPythonApplication,
     base_aliases,
@@ -791,7 +791,7 @@ def start(self) -> None:
         run(self._start, backend=backend)
 
     async def _wait_to_enter_eventloop(self) -> None:
-        await self.kernel._eventloop_set.wait()
+        await to_thread.run_sync(self.kernel._eventloop_set.wait)
         await self.kernel.enter_eventloop()
 
     async def main(self) -> None:

ipykernel/kernelbase.py

@@ -235,7 +235,7 @@ def _parent_header(self):
         "list_subshell_request",
     ]
 
-    _eventloop_set: Event = Event()
+    _eventloop_set = threading.Event()
 
     def __init__(self, **kwargs):
         """Initialize the kernel."""