[Stackless] Re: [Python-Dev] Stackless pages

[Greg Ewing]

Jeremy Hylton <jeremy at alum.mit.edu>:

> Are continuations necessary to implement them or are
> there other options?

I think you'll find that any implementation of microthreads
or coroutines or whatever you want to call them, that
doesn't rely on playing nonportable tricks with the C
stack, will be just as mindbending as Stackless.

> The problem is that continuations break the notion a C API call will
> always return an answer;

So do threads or coroutines. As soon as you have multiple
threads of control, you have the chance that one of them
will switch to another and never get back.

> I assume Stackless raises an error in this case,
> but this seems pretty messy

This messiness isn't the fault of Stackless itself, but of the
large amount of code which *hasn't* been converted to the
Stackless Way. If the whole of Python and everything that
it calls were made truly stackless, the problem would not
arise.

Doing so, however, would not be fun. It wouldn't be fun
for any future extension writers, either.

I can't see any way out of this. Continuations/coroutines/
microthreads are all basically the same thing underneath, and
they imply an execution model that just doesn't fit well
with C.

Maybe we need to reimplement Python in Scheme, and then
feed it through a good Scheme compiler. SPython, anyone? 

Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
Christchurch, New Zealand	   | wholly-owned subsidiary of USA Inc.  |
greg at cosc.canterbury.ac.nz	   +--------------------------------------+
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