[Web-SIG] [PEP 444] Future- and Generator-Based Async Idea

[Alice Bevan–McGregor]

Warning: this assumes we're running on bizzaro-world PEP 444 that 
mandates applications are generators.  Please do not dismiss this idea 
out of hand but give it a good look and maybe some feedback.  ;)

--

Howdy!

I've finished touching up the p-code illustrating my idea of using 
generators to implement async functionality within a WSGI application 
and middleware, including the idea of a wsgi2ref-supplied decorator to 
simplify middleware.

	https://gist.github.com/770743

There may be a few typos in there; I switched from the idea of passing 
back the returned value of the future to passing back the future itself 
in order to better handle exception handling (i.e. not requiring utter 
insanity in the middleware to determine the true source of an exception 
and the need to pass it along).

The second middleware demonstration (using a decorator) makes 
middleware look a lot more like an application: yielding futures, or a 
response, with the addition of yielding an application callable not 
explored in the first (long, but trivial) example.  I believe this 
should cover 99% of middleware use cases, including interactive 
debugging, request routing, etc. and the syntax isn't too bad, if you 
don't mind standardized decorators.

This should be implementable within the context of Marrow HTTPd 
(http://bit.ly/fLfamO) without too much difficulty.

As a side note, I'll be adding threading support to the server 
(actually, marrow.server, the underlying server/protocol abstraction 
m.s.http utilizes) using futures some time over the week-end by 
wrapping the async callback that calls the application with a call to 
an executor, making it immune to blocking, but I suspect the overhead 
will outweigh the benefit for speedy applications.

Testing multi-process vs. multi-threaded using 2 workers each and the 
prime calculation example, threading is 1.5x slower for CPU-intensive 
tasks under Python 2.7.  That's terrible.  It should be 2x; I have 2 
cores.  :/

	- Alice.