[Stackless] Re: [Python-Dev] uthread strawman

Christian Tismer tismer at tismer.com
Fri Nov 10 12:39:24 CET 2000

Bill Tutt wrote:
> Guido van Rossum [mailto:guido at python.org] wrote:
> > > Christian Tismer wrote:
> > > > Does anybody know of a useful example where continuations
> > > > are really needed?
> > [Bill Tutt]

Bill on [server architecture, async state machine]

> > Indeed, this kind of server architecture is typically done with
> > coroutines -- it's not a good argument for the full power of
> > continuations. :-)
> Hrm, but can I get enough info from the coroutine support to
> automatically determine which "work item queue" the paused routine
> should go into after the "blocking" operation completes?
> Additionally, the coroutine can't be stuck to only one system
> thread. That would be bad.

Coroutine vs. continuation isn't the point here, I think.
What you would likely need is gathering information about
the frames and variables in your co-whatever. This is quite
simple to implement, with either architecture.
My next version will not only allow to inspect the eval
stack of a frame, but also inspection and modification
of local variables; still this is no continuation feature.
We can simply inspect anything.

What makes the difference is callability:
Whenever we expose arbitrary frames as callable objects,
or we provide an unrestricted other way to execute them,
then exactly all the problems and consequences of
continuations pop up: we need to clone execution state,
since now it is possible to have more than one state for
a frame.
If we avoid this, we can still have all control and debugging
features with coroutines.

ciao - chris

Christian Tismer             :^)   <mailto:tismer at tismer.com>
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