[RFC] EventListener design for Python Async QMP library

[John Snow]

Hi all: I am continuing work on my asyncio-based QMP library for Python, 
which adds support for OOB executions, multiple simultaneous pending 
executions, and truly asynchronous event handling.

The library is what will fundamentally power the new qmp-shell that 
Niteesh is working on for his GSoC project this summer.

I would like to solicit feedback on one component of the design in 
particular: An interface I call the EventListener, which is an API 
designed to allow multiple concurrent coroutines to safely wait for and 
consume QMP events.

I have a document explaining their use on my GitLab fork. At the bottom 
of the document is a list of my own complaints about my design. If you'd 
like to take a peek at what I am cooking up and would like to offer 
feedback, now would be a pretty good time to do it before we get too far 
into development for the new qmp-shell.

The document is here: https://gitlab.com/jsnow/qemu/-/snippets/2133449

Any feedback, thoughts, etc are appreciated.

Thanks,
--js


Oh, and: The full library (Warning, with outdated docs, no tests, and 
quite a few TODO/FIXMEs scattered about) is here:

https://gitlab.com/jsnow/qemu/-/tree/python-async-qmp-aqmp/python/qemu/aqmp

But it's not in a state to ask for critique on the entire architecture 
just yet, there are still a few more suggestions from Stefan to 
implement from the last time I did so.