[Stackless] Does stackless only work with pure Python codes?

Christian Tismer tismer at stackless.com
Fri Nov 26 16:26:57 CET 2004

Limin Fu wrote:
> Hello everybody,
> Using stackless in python to simulate multithread
> sounds interesting. But I wonder what will happen with
> stackless if a python program will use loaded C
> modules, since the C module can not be divided into
> tiny task by Python codes.

If a C module is running, Stackless can't do anything.
If the C module calls back into Python and executes
bytecodes, then Stackless is active, again, and it is
possible to switch tasklets, even if there is still
an active C function on the C stack. In this situation,
Stackless modifies the C stack to perform switches.
This way of switching has been the one and only in
Stackless 2.0. In 3.0, I try to avoid fiddling the
C stack at all, because it is much faster. But for
cases like this, it is a powerful technique.

Again to your question: If a C extension happens
to stay in C code for a long time, then we cannot
switch during this time. It would be easy to modify
the extension a bit and make it run a few bytecodes
from time to time, or have it explicitly run the
stackless "schedule" function in order to give up
its time slice.

ciao - chris

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