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Stackless Python and Python 2.x

Gordon McMillan gmcm at hypernet.com
Sun Sep 2 08:06:48 EDT 2001 
[Joal Heagney]
>> Wasn't a big part of the generator addition that it supplies a
>> simpler-to-understand solution to the majority of continuations
>> solutions? 

[Tim Peters] 
> I expect that if you dug into all the applications using Stackless,
> you'd find that the majority of them rely on full-blown coroutines or
> microthreads.  It's unclear how far PEP 255's "Simple Generators" can
> be pushed towards those specific ends.

Alas, not far enough. I've used Stackless a number of times to 
turn state machines inside out (where the number of events is
smallish but the state stuff is complex, this is a wonderful
simplification). Generally this means that there's a whole 
set of frames hanging around when I "yield".

To the non-coroutine aware, this is better explained from a 
thread POV - I have a bunch of "threads" that are dispatched
when an event is received, and only swap out when they want to.

The advantages over real threads are enormous:
 - lightweight 
 - system level locks never needed
 - user level locks rarely needed

The only downside is relatively minor - I have to make
sure that one "thread" doesn't monopolize the CPU.
 
> Neil Schemenauer discovered that it was possible to code the
> "traditional" coroutine examples using simple generators instead...

Yah, well your "traditional" thread example prints the numbers
1 through 10 twice in some interleaving...

- Gordon
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