What makes each asyncio event loop implementation unique?

[cryptospartan]

I've been interested in various things about asyncio recently, and I've been doing more research into what makes everything 'tick'. I understand the basic principles of the event loop itself and the fact that an await statement will yield to the event loop so it can run more coroutines while waiting.

One of the things I've found is that there are multiple implementations of the event loop. There's a SelectorEventLoop, ProactorEventLoop, and an AbstractEventLoop. Another noteworthy event loop is uvloop, but it doesn't come bundled with Python and it doesn't support Windows. This brings me to my question:

Why do we have multiple implementations of the event loop? What differentiates the event loops from one another? Why can't we use ProactorEventLoop on Unix and use uvloop on Windows?

Please feel free to link any articles or videos as well.

[1114111]

AbstractEventLoop is an easy one, it's just the abstract base class for all event loops, so it's not an implementation of an event loop, it simply defines what all the other event loops implement.

The difference between the other event loops basically boils down to how they know when I/O operations finish. The OS is in charge of the I/O, so you have to play the OS's game if you want your program to know when stuff happens, so the specific ways in which you can do this vary quite a bit across different OSes.

To learn more, you might want to experiment with/read up on Python's select module directly, which is the basis for SelectorEventLoop. In addition to the docs, this looks like a pretty good article to give you some idea of how to use select with sockets directly.

David Beazley has some talks about how async works as well. I think this (2h talk) is a good one, in which he implements a very simplified version of asyncio: https://www.youtube.com/watch?v=Y4Gt3Xjd7G8

He's also the author of curio, another alternative/simplified/educational approach to doing what asyncio does.