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Worker with ZeroMQ does not work on Windows with default configuration #524
Description
Asynchronous ZeroMQ does not work on Windows with default asyncio.WindowsProactorEventLoopPolicy.
It raises:
RuntimeError: Proactor event loop does not implement add_reader family of methods required for zmq. zmq will work with proactor if tornado >= 6.1 can be found.
Use `asyncio.set_event_loop_policy(WindowsSelectorEventLoopPolicy())` or install 'tornado>=6.1' to avoid this error.
If I install tornado as required by the exception, then the worker starts, but there is a warning that I need to configure the eventloop.
RuntimeWarning: Proactor event loop does not implement add_reader family of methods required for zmq. Registering an additional selector thread for add_reader support via tornado. Use `asyncio.set_event_loop_policy(WindowsSelectorEventLoopPolicy())` to avoid this warning.
self._get_loop()
Adding asyncio.set_event_loop_policy(WindowsSelectorEventLoopPolicy()) to the application code has no effect for worker
Activity
raidzin commentedon Oct 24, 2025
@s3rius, I see two ways to solve this problem:
tornadoas a platform-specific dependency when we use the optionalzmqdependency. With this, the worker will start, but the warning will remainpyzmqis installed andos.name == 'nt'and then change the defaultEventLoopPolicytoWindowsSelectorEventLoopPolicywhen worker startsTo be honest, I can't say exactly what side effects the second option might have, but I tested on pure
pyzmqand it worked without atornado[-]Bug: Worker with ZeroMQ does not work on Windows with default configuration[/-][+]Worker with ZeroMQ does not work on Windows with default configuration[/+]danfimov commentedon Sep 17, 2026
The second option seems more optimal to me. I don't have Windows handy to test it myself, so if you try it out and come up with a fix, I'd be happy to review it)