Use tornado 6.2's PeriodicCallback in restarter

.github/workflows/downstream.yml

@@ -76,7 +76,6 @@ jobs:
           git clone https://github.com/jupyter/jupyter_kernel_test.git
           cd jupyter_kernel_test
           conda env update --name jupyter_kernel_test --file environment.yml
-          conda install -c conda-forge xeus-cling
           pip install -e ".[test]"
           python -m unittest -v
 

jupyter_client/ioloop/restarter.py

@@ -5,15 +5,12 @@
 """
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
-import asyncio
 import time
 import warnings
 
 from traitlets import Instance
-from zmq.eventloop import ioloop
 
 from jupyter_client.restarter import KernelRestarter
-from jupyter_client.utils import run_sync
 
 
 class IOLoopKernelRestarter(KernelRestarter):
@@ -27,19 +24,19 @@ def _loop_default(self):
             DeprecationWarning,
             stacklevel=4,
         )
+        from zmq.eventloop import ioloop
+
         return ioloop.IOLoop.current()
 
     _pcallback = None
 
     def start(self):
         """Start the polling of the kernel."""
         if self._pcallback is None:
-            if asyncio.iscoroutinefunction(self.poll):
-                cb = run_sync(self.poll)
-            else:
-                cb = self.poll
-            self._pcallback = ioloop.PeriodicCallback(
-                cb,
+            from tornado.ioloop import PeriodicCallback
+
+            self._pcallback = PeriodicCallback(
+                self.poll,
                 1000 * self.time_to_dead,
             )
             self._pcallback.start()

pyproject.toml

@@ -29,7 +29,7 @@ dependencies = [
     "nest-asyncio>=1.5.4",
     "python-dateutil>=2.8.2",
     "pyzmq>=23.0",
-    "tornado>=6.0",
+    "tornado>=6.2",
     "traitlets",
 ]