For python<3.10 ensure control_lock created in thread that uses it

Author: ianthomas23

ipykernel/kernelbase.py

@@ -247,7 +247,7 @@ def _parent_header(self):
     execution_count = 0
 
     # Asyncio lock to ensure only one control queue message is processed at a time.
-    _control_lock = asyncio.Lock()
+    _control_lock = asyncio.Lock
 
     msg_types = [
         "execute_request",
@@ -543,6 +543,10 @@ def schedule_dispatch(self, dispatch, *args):
         # ensure the eventloop wakes up
         self.io_loop.add_callback(lambda: None)
 
+    async def _create_control_lock(self):
+        # This can be removed when minimum python increases to 3.10
+        self._control_lock = asyncio.Lock()
+
     def start(self):
         """register dispatchers for streams"""
         self.io_loop = ioloop.IOLoop.current()
@@ -552,6 +556,14 @@ def start(self):
         if self.control_stream:
             self.control_stream.on_recv(self.dispatch_control, copy=False)
 
+        if self.control_thread and sys.version_info < (3, 10):
+            # Before Python 3.10 we need to ensure the _control_lock is created in the
+            # thread that uses it. When our minimum python is 3.10 we can remove this
+            # and always use the else below, or just assign it where it is declared.
+            self.control_thread.io_loop.add_callback(self._create_control_lock)
+        else:
+            self._control_lock = asyncio.Lock()
+
         if self.shell_stream:
             self.shell_stream.on_recv(
                 partial(