How to implement an async message bus

[Nagy László Zsolt]

>>>>     try:
>>>>         return await waiter
>>>>     finally:
>>>>         # TODO: Use a context manager to add and remove the keys.
>>>>         for key in keys:
>>>>             self._waiters[key].discard(waiter)
>>>>         if handle:
>>>>             handle.cancel()
>>>>
>>>> def notify(self, key, message):
>>>>     if key in self._waiters and self._waiters[key]:
>>>>         waiter = next(iter(self._waiters[key]))
>>>>         waiter.set_result((key, message))
>>> I think this is what I needed. I'm going to try this tomorrow.
>> Yes, putting aside the asyncio/tornado distinction, I think a Future
>> will still solve the problem for you.
> No, it won't. :-( 
>
> Finally, I got it working, by replacing asyncio.Future with
> tornado.concurrent.Future.
>
> At least it is consistent. But it is also missing key features. For
> example, there is no tornado.concurrent.Condition.
I was corrected, as follows:

> asyncio.Futures depend on the asyncio event loop, so you must
> configure Tornado to use the asyncio loop:
>
>    
> tornado.ioloop.IOLoop.configure('tornado.platform.asyncio.AsyncIOMainLoop')
>
> This could definitely use some better documentation. It would be nice
> if it could fail in a more graceful way (give an error message instead
> of hanging), but I'm not sure if there's any way to do that.
>

So tornado can be used with asyncio, but it requires configuration (and
it is not yet very well documented).

> Also, for your python-list message: there is now (since 4.2) a Tornado
> Condition class, but it lives in tornado.locks instead of
> tornado.concurrent.

There is a little incosistency here, but at least there is a Condition
class.

I think the tornado team is trying to make tornado fully compatible with
asyncio, just the are not there yet.


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