Fix kernel restart

jupyter_server_documents/kernels/kernel_client.py

@@ -80,7 +80,7 @@ async def stop_listening(self):
         """
         # If the listening task isn't defined yet
         # do nothing.
-        if not self._listening_task:
+        if not hasattr(self, '_listening_task') or not self._listening_task:
             return
 
         # Attempt to cancel the task.
@@ -93,6 +93,9 @@ async def stop_listening(self):
         # Log any exceptions that were raised.
         except Exception as err:
             self.log.error(err)
+        finally:
+            # Clear the task reference
+            self._listening_task = None
 
     _listening_task: t.Optional[t.Awaitable] = Any(allow_none=True)
 

jupyter_server_documents/kernels/kernel_manager.py

@@ -127,8 +127,9 @@ async def connect(self):
             await asyncio.sleep(0.1)
 
     async def disconnect(self):
-        await self.main_client.stop_listening()
-        self.main_client.stop_channels()
+        if self.main_client:
+            await self.main_client.stop_listening()
+            self.main_client.stop_channels()
 
     async def broadcast_state(self):
         """Broadcast state to all listeners"""

jupyter_server_documents/kernels/multi_kernel_manager.py

@@ -7,4 +7,11 @@ def start_watching_activity(self, kernel_id):
         pass
 
     def stop_buffering(self, kernel_id):
-        pass
+        pass
+
+    # NOTE: Since we disable watching activity and buffering here, 
+    # this method needs to be forked and remove code related to these things. 
+    async def restart_kernel(self, kernel_id, now=False):
+        """Restart a kernel by kernel_id"""
+        self._check_kernel_id(kernel_id)
+        await self.pinned_superclass._async_restart_kernel(self, kernel_id, now=now)