[Stackless] Sprinting at PyCon

Kristján Valur Jónsson kristjan at ccpgames.com
Mon Apr 14 15:44:13 CEST 2014

Hi there.

I'm not entirely sure about the benefit of such a re-architecture.
As I see it the chief benefits of Stackless over greenlets, are:
1) Pickling of runtime state.
2) Scheduling and higher level primitives implemented in C
3) "stackless" excecution of certain builtin python things. (soft switching as opposed to stack slicing) .  Allows for example soft stack switch in an __enter__/__exit__ method (an experimental feature).   Soft switching primarily allows tasklet state to be pickled and restored, but it is supposedly also for performance of execution of regular python code (this last claim is unproven)

If we didn't need either, we could implement stackless as a .py module that relies on greenlets.  Then "stackless" would be just another greenlet client.

Pickling can certainly be implemented in a more slim implementation, but picling of an execution state relies on "soft" switching.  
Reasoning about the performance is harder but we always want to be fast :)

So, what can we throw away and how can we restructure to make things simpler, while keeping the essential benefits of stackless?

-----Original Message-----
From: stackless-bounces at stackless.com [mailto:stackless-bounces at stackless.com] On Behalf Of Alain Poirier
Sent: 13. apríl 2014 16:08
To: stackless at stackless.com
Subject: [Stackless] Sprinting at PyCon

Hi all,

I would like to discuss how it'd be possible or not for Stackless to follow the same path than PyPy:

  - A simpler Stackless core, with only the 'tealet' / '_continuation' stack
    switch, writing in C. Exposing the same API than PyPy.
    IIRC, Krisjan already has such a Stackless version.

  - All the high level features of Stackless like Tasklets and Channels moved to
    the 'stackless.py' pure Python module.

  - An emulation of the greenlets API, in a 'greenlet.py' pure Python module.

  - Bonus point if these 'stackless.py' and 'greenlet.py' modeules are shared /
    co-developed with the PyPy project :)

I see several advantages then:

  - Greenlets and Stackless features being Python modules, easier experimentations
    are possible. For example writing other scheduling policy or higher concurrency
    primitives such like Andrew's select/join.

  - With a 'greenlet.py' compatible module, lots of softwares like 'gevent' could
    work without any modification.

  - Works on 'greenlet.py' and 'stackless.py' can profit both to Python Stackless
    and PyPy.

Just my 2 cents,

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