Try to reuse already created connection and channel while emitting from external processes

[theDigitalGuy]

to avoid rabbitmq starting to block connections.

Problem description: theDigitalGuy@4ff70fb#commitcomment-76278910

[miguelgrinberg]

Hi, thanks for this. There's two problems:

1. Your solution is not robust enough. It should handle random disconnects and retries. See the Redis implementations to have an idea of what is expected.
2. The Kombu and aiopika implementations are more or less the same. If one is improved, the other should be improved in the same way.

Do you think you can address these?

[sillyfrog]

Regarding (1), the RobustConnection object returned by connect_robust actively reconnects on errors/disconnects etc. I've done extensive testing in single node and clustered configurations to confirm it's very robust.

While there is no connection to the server an error is raised, but as soon as connectivity is restored, things start working again as you would hope, (probably) negating the need for this to be re-implemented in python-socketio.

[sillyfrog]

This should have a lock around it as if there are several calls in close succession, it'll create several new connections. See #1142 for an example of this in use.

[miguelgrinberg]

Fixed by cd7f781.