Folly Futures to Python Asyncio Futures Bridge

Folly Futures to Python Asyncio Futures Bridge

Summary:
folly/python/futures.h provides some helper functions for bridging folly::future to asyncio.Future.

folly/python/NotificationQueueExecutor.h is a Driveable executor that has a fileno() method that can be monitored using (select, epoll) to determine if the drive method should be called.

folly/python/executor.pyx is an implementation of a "driver" for the NotificationQueueExecutor from the python asyncio side. It tracks also keeps track of asyncio eventloops to Executor mappings.

the getExecutor() from folly/python/futures.h uses that mapping to return the correct executor for this python thread.

Reviewed By: andriigrynenko, yfeldblum

Differential Revision: D4687029

fbshipit-source-id: e79314606ffa18cb6933fe6b749991bfea646cde