Starting a viewer in a separate thread with multiprocessing fails with tornado 6.0.3

[mvdoc]

It works with tornado 4.3. This comes from our realtimefmri pipeline. The error appears before the client can connect. Traceback:

realtimefmri_1_96c86fa3cd6a | Started server on port 8051
realtimefmri_1_96c86fa3cd6a | <IPython.core.display.HTML object>
realtimefmri_1_96c86fa3cd6a | Process Process-5:
realtimefmri_1_96c86fa3cd6a | Traceback (most recent call last):
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/multiprocessing/process.py", line 297, in _bootstrap
realtimefmri_1_96c86fa3cd6a |     self.run()
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/multiprocessing/process.py", line 99, in run
realtimefmri_1_96c86fa3cd6a |     self._target(*self._args, **self._kwargs)
realtimefmri_1_96c86fa3cd6a |   File "/app/realtimefmri/realtimefmri/viewer.py", line 80, in serve
realtimefmri_1_96c86fa3cd6a |     viewer = PyCortexViewer(surface, transform, mask_type, vmin, vmax)
realtimefmri_1_96c86fa3cd6a |   File "/app/realtimefmri/realtimefmri/viewer.py", line 32, in __init__
realtimefmri_1_96c86fa3cd6a |     view = server.get_client()
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/site-packages/cortex/webgl/view.py", line 802, in get_client
realtimefmri_1_96c86fa3cd6a |     return JSMixer(self.send, "window.viewer")
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/site-packages/cortex/webgl/serve.py", line 318, in __init__
realtimefmri_1_96c86fa3cd6a |     self.attrs = self.send(method='query', params=[self.name])[0]
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/site-packages/cortex/webgl/serve.py", line 301, in send
realtimefmri_1_96c86fa3cd6a |     sock.write_message(msg)
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/site-packages/tornado/websocket.py", line 342, in write_message
realtimefmri_1_96c86fa3cd6a |     return self.ws_connection.write_message(message, binary=binary)
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/site-packages/tornado/websocket.py", line 1098, in write_message
realtimefmri_1_96c86fa3cd6a |     fut = self._write_frame(True, opcode, message, flags=flags)
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/site-packages/tornado/websocket.py", line 1075, in _write_frame
realtimefmri_1_96c86fa3cd6a |     return self.stream.write(frame)
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/site-packages/tornado/iostream.py", line 555, in write
realtimefmri_1_96c86fa3cd6a |     future = Future()  # type: Future[None]
realtimefmri_1_96c86fa3cd6a |   File "/usr/local/lib/python3.7/asyncio/events.py", line 644, in get_event_loop
realtimefmri_1_96c86fa3cd6a |     % threading.current_thread().name)
realtimefmri_1_96c86fa3cd6a | RuntimeError: There is no current event loop in thread 'Thread-1068'.