I got really curious about this and went and did some research.  With some really platform-specific hackery on every platform, you can mostly figure it out; completely on OS X and Windows, although (as far as I can tell) only partially on Linux and FreeBSD.

I'm not sure if it's possible to make use of these facilities without a Twisted-style event-loop though.  If anybody's interested, I recorded the results of my research in a comment on the Twisted ticket for this: <http://twistedmatrix.com/trac/ticket/2424#comment:26>.

-glyph