Fix compatibility with tornado 6.2 beta (#956)

Co-authored-by: Steven Silvester <steven.silvester@ieee.org>

ipykernel/control.py

@@ -1,24 +1,17 @@
 from threading import Thread
 
-import zmq
-
-if zmq.pyzmq_version_info() >= (17, 0):
-    from tornado.ioloop import IOLoop
-else:
-    # deprecated since pyzmq 17
-    from zmq.eventloop.ioloop import IOLoop
+from tornado.platform.asyncio import AsyncIOLoop
 
 
 class ControlThread(Thread):
     def __init__(self, **kwargs):
         Thread.__init__(self, name="Control", **kwargs)
-        self.io_loop = IOLoop(make_current=False)
+        self.io_loop = AsyncIOLoop(make_current=False)
         self.pydev_do_not_trace = True
         self.is_pydev_daemon_thread = True
 
     def run(self):
         self.name = "Control"
-        self.io_loop.make_current()
         try:
             self.io_loop.start()
         finally:

ipykernel/iostream.py

@@ -17,14 +17,11 @@
 from weakref import WeakSet
 
 import zmq
-
-if zmq.pyzmq_version_info() >= (17, 0):
-    from tornado.ioloop import IOLoop
-else:
-    # deprecated since pyzmq 17
-    from zmq.eventloop.ioloop import IOLoop
-
 from jupyter_client.session import extract_header
+
+# AsyncIOLoop always creates a new asyncio event loop,
+# rather than the default AsyncIOMainLoop
+from tornado.platform.asyncio import AsyncIOLoop
 from zmq.eventloop.zmqstream import ZMQStream
 
 # -----------------------------------------------------------------------------
@@ -63,7 +60,7 @@ def __init__(self, socket, pipe=False):
         self.background_socket = BackgroundSocket(self)
         self._master_pid = os.getpid()
         self._pipe_flag = pipe
-        self.io_loop = IOLoop(make_current=False)
+        self.io_loop = AsyncIOLoop(make_current=False)
         if pipe:
             self._setup_pipe_in()
         self._local = threading.local()
@@ -78,7 +75,6 @@ def __init__(self, socket, pipe=False):
 
     def _thread_main(self):
         """The inner loop that's actually run in a thread"""
-        self.io_loop.make_current()
         self.io_loop.start()
         self.io_loop.close(all_fds=True)