Flaky `test_host_uses_scheduler_protocol`

[gjoseph92]

Failed on macOS, 3.8. The timeout error is remarkably inscrutable, it's not clear where in the test it's timing out. I would assume it's something about opening connections as usual, probably the worker trying to connect to the scheduler.

distributed/distributed/tests/test_worker.py

Lines 1446 to 1463 in 1bb0ce7

	@gen_test()
	async def test_host_uses_scheduler_protocol(monkeypatch):
	# Ensure worker uses scheduler's protocol to determine host address, not the default scheme
	# See https://github.com/dask/distributed/pull/4883
	from distributed.comm.tcp import TCPBackend
	class BadBackend(TCPBackend):
	def get_address_host(self, loc):
	raise ValueError("asdf")
	monkeypatch.setitem(backends, "foo", BadBackend())
	with dask.config.set({"distributed.comm.default-scheme": "foo"}):
	async with Scheduler(protocol="tcp", dashboard_address=":0") as s:
	async with Worker(s.address):
	# Ensure that worker is able to properly start up
	# without BadBackend.get_address_host raising a ValueError
	pass

______________________ test_host_uses_scheduler_protocol _______________________

args = ()
kwds = {'monkeypatch': <_pytest.monkeypatch.MonkeyPatch object at 0x7fb435861040>}

    @wraps(func)
    def inner(*args, **kwds):
        with self._recreate_cm():
>           return func(*args, **kwds)

../../../miniconda3/envs/dask-distributed/lib/python3.8/contextlib.py:75: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../../miniconda3/envs/dask-distributed/lib/python3.8/contextlib.py:75: in inner
    return func(*args, **kwds)
distributed/utils_test.py:728: in test_func
    return _run_and_close_tornado(async_fn_outer, func, *args, **kwargs)
distributed/utils_test.py:376: in _run_and_close_tornado
    return asyncio.run(inner_fn())
../../../miniconda3/envs/dask-distributed/lib/python3.8/asyncio/runners.py:44: in run
    return loop.run_until_complete(main)
../../../miniconda3/envs/dask-distributed/lib/python3.8/asyncio/base_events.py:616: in run_until_complete
    return future.result()
distributed/utils_test.py:373: in inner_fn
    return await async_fn(*args, **kwargs)
distributed/utils_test.py:716: in async_fn_outer
    return await asyncio.wait_for(
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

fut = <Task cancelled name='Task-117593' coro=<test_host_uses_scheduler_protocol() done, defined at /Users/runner/work/distributed/distributed/distributed/tests/test_worker.py:1446>>
timeout = 30

    async def wait_for(fut, timeout, *, loop=None):
        """Wait for the single Future or coroutine to complete, with timeout.
    
        Coroutine will be wrapped in Task.
    
        Returns result of the Future or coroutine.  When a timeout occurs,
        it cancels the task and raises TimeoutError.  To avoid the task
        cancellation, wrap it in shield().
    
        If the wait is cancelled, the task is also cancelled.
    
        This function is a coroutine.
        """
        if loop is None:
            loop = events.get_running_loop()
        else:
            warnings.warn("The loop argument is deprecated since Python 3.8, "
                          "and scheduled for removal in Python 3.10.",
                          DeprecationWarning, stacklevel=2)
    
        if timeout is None:
            return await fut
    
        if timeout <= 0:
            fut = ensure_future(fut, loop=loop)
    
            if fut.done():
                return fut.result()
    
            await _cancel_and_wait(fut, loop=loop)
            try:
                fut.result()
            except exceptions.CancelledError as exc:
                raise exceptions.TimeoutError() from exc
            else:
                raise exceptions.TimeoutError()
    
        waiter = loop.create_future()
        timeout_handle = loop.call_later(timeout, _release_waiter, waiter)
        cb = functools.partial(_release_waiter, waiter)
    
        fut = ensure_future(fut, loop=loop)
        fut.add_done_callback(cb)
    
        try:
            # wait until the future completes or the timeout
            try:
                await waiter
            except exceptions.CancelledError:
                if fut.done():
                    return fut.result()
                else:
                    fut.remove_done_callback(cb)
                    # We must ensure that the task is not running
                    # after wait_for() returns.
                    # See https://bugs.python.org/issue32751
                    await _cancel_and_wait(fut, loop=loop)
                    raise
    
            if fut.done():
                return fut.result()
            else:
                fut.remove_done_callback(cb)
                # We must ensure that the task is not running
                # after wait_for() returns.
                # See https://bugs.python.org/issue32751
                await _cancel_and_wait(fut, loop=loop)
>               raise exceptions.TimeoutError()
E               asyncio.exceptions.TimeoutError

../../../miniconda3/envs/dask-distributed/lib/python3.8/asyncio/tasks.py:501: TimeoutError

https://github.com/dask/distributed/runs/7999878381?check_suite_focus=true#step:11:1718