websocket: Task was destroyed but it is pending!

[gdbrianlu]

[E 191029 10:54:51 base_events:1608] Task was destroyed but it is pending!
task: <Task pending coro=<WebSocketProtocol13._receive_frame_loop() done, defined at D:\AndroidControl\Python37\lib\site-packages\tornado\websocket.py:1115> wait_for=<Future pending cb=[IOLoop.add_future..() at D:\AndroidControl\Python37\lib\site-packages\tornado\ioloop.py:690, <TaskWakeupMethWrapper object at 0x000002AC48174468>()]> cb=[IOLoop.add_future..() at D:\AndroidControl\Python37\lib\site-packages\tornado\ioloop.py:690]>

[bdarnell]

If this message occurs while the process is shutting down, it's generally harmless - it just means that the process is only partially cleaning up after itself. I recommend ignoring it, but if you want to work towards a cleaner shutdown, you need to close all your websocket connections before stopping the event loop.

This message comes from asyncio rather than Tornado, so there's not much Tornado can do to control it.

[afzoun]

If this message occurs while the process is shutting down, it's generally harmless - it just means that the process is only partially cleaning up after itself. I recommend ignoring it, but if you want to work towards a cleaner shutdown, you need to close all your websocket connections before stopping the event loop.

This message comes from asyncio rather than Tornado, so there's not much Tornado can do to control it.

I have the same RuntimeWarning, but it doesn't occur only on shut down. I get this warning constantly while my websocket is open. I know it comes from asyncio, but the Tornado is talking to asyncio.

I am using tornado 6.0.3 with python 3.7

[bdarnell]

Hmm. There's only one receive_frame_loop call per websocket connection, so it shouldn't be possible to see this more than once while the connection is alive. Are you sure something's not closing and reopening the connection? But even if it is, it's not expected to see this message at any time but shutdown. Can you provide any kind of reproducible test case?

Are you also on windows? There are reports of issues with websockets on windows that are not understood: #2136.

[tankienleong]

Hi @bdarnell , I faced the same problem as @afzoun.

you can reproduce the error by running the cam_server.py.

Please rename the index.txt to index.html (github does not allow me upload html file)
index.txt

Please rename the cam_server.txt to cam_server.py (github does not allow me upload python file)
cam_server.txt

[ploxiln]

@tankienleong in your example you call write_message() on CamWSHandler instances from the gstreamer callback pull_frame(), which runs in a different thread than the ioloop of the async http/websocket server. That is a problem, you are not supposed to do that. The only thing you can do to interact with tornado stuff from other threads, is call the appropriate ioloop's add_callback() method, and then do the other tornado related calls in that callback. I think that AnyThreadEventLoopPolicy does not really help you here.