[Python-Dev] 'stackless' python?

[Christian Tismer]

Guido van Rossum wrote:

[setjmp/longjmp -no-no]

> Forget about it.  setjmp/longjmp are invitations to problems.  I also
> assume that they would interfere badly with C++.
> 
> > I think just about any Scheme implementation has to solve this same
> > problem... I'll dig through my collection of them for ideas.
> 
> Anything that assumes knowledge about how the C compiler and/or the
> CPU and OS lay out the stack is a no-no, because it means that the
> first thing one has to do for a port to a new architecture is figure
> out how the stack is laid out.  Another thread in this list is porting
> Python to microplatforms like PalmOS.  Typically the scheme Hackers
> are not afraid to delve deep into the machine, but I refuse to do that
> -- I think it's too risky.
...

I agree that this is generally bad. While it's a cakewalk
to do a stack swap for the few (X86 based:) platforms where
I work with. This is much less than a thread change.

But on the general issues:
Can the Python-calls-C and C-calls-Python problem just be solved
by turning the whole VM state into a data structure, including
a Python call stack which is independent? Maybe this has been
mentioned already.

This might give a little slowdown, but opens possibilities
like continuation-passing style, and context switches
between different interpreter states would be under direct
control.

Just a little dreaming: Not using threads, but just tiny
interpreter incarnations with local state, and a special
C call or better a new opcode which activates the next
state in some list (of course a Python list).
This would automagically produce ICON iterators (duck)
and coroutines (cover).
If I guess right, continuation passing could be done
by just shifting tiny tuples around. Well, Tim, help me :-)

[closures]

> > I think this is a great idea.  I've been staring at python bytecodes a
> > bit lately thinking about how to do something like this, for some
> > subset of Python.

Lumberjack? How is it going? [to Sam]

ciao - chris

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