Quick update before I head to bed.

Thank you for the input, I had gotten the individual async calls working a couple days ago, and I was just working to replace the communicate() method for Windows.

Yes, I'm using asyncio._overlapped, though asyncio uses subprocessing, so I needed to defer import of _overlapped until one of a couple crucial methods were being called in order to prevent issues relating to circular imports.

I also ended up moving asyncio.windows_utils.pipe out to subprocess, as copying/pasting it for a third 'create an overlapped-io pipe' implementation for the standard library just doesn't make a lot of sense, and another circular import seemed like a bad idea. If/when subprocess goes away completely, someone else can move the function back.

With overlapped IOs able to be cancelled, it's not all that bad to make a completely re-entrant communicate() without threads, though I made a few mistakes in my first pass tonight that I need to fix tomorrow.