Problem with `timed_window` with asyncio

[snth]

Hi,

When I try to use the timed_window function with the asyncio event loop I get the following error:

AttributeError: 'AsyncIOMainLoop' object has no attribute '_running'

For example if you change line 12 of the `fib_asyncio.py" example to:

s.timed_window(1.0).sink(lambda x: print(x))

then I get:

$ python fib_asyncio.py
Traceback (most recent call last):
  File "fib_asyncio.py", line 14, in <module>
    source.emit(0)                          # seed with initial values
  File "/opt/venv-numismatic/lib/python3.6/site-packages/streamz/core.py", line 219, in emit
    return sync(self.loop, _)
  File "/opt/venv-numismatic/lib/python3.6/site-packages/streamz/core.py", line 1068, in sync
    if not loop._running:
AttributeError: 'AsyncIOMainLoop' object has no attribute '_running'

[mrocklin]

Yeah, that's a bug. The check on IOLoop._running is Tornado-specific. Fortunately, that check is also a historical artifact, and can be removed without a problem. @snth do you have any interest in submitting a PR that removes this conditional block and perhaps also includes a small test? We should have some asyncio tests.

[snth]

@mrocklin Could you describe why it is safe to remove those checks? I didn't look at more than 2 or 3 lines around the line that caused the problem so don't understand the overall context and how that code integrates into the bigger picture.

[mrocklin]

They aren't used within this project. The utility sync function was pulled from Dask, where that functionality was previously needed. It has no effect in this project.