[Stackless] Re: [Python-Dev] Stackless Design Q. (original) (raw)

Christian Tismer tismer@tismer.com
Thu, 21 Feb 2002 14:48:07 +0100

Jeff Senn wrote:

Greg Ewing <greg@cosc.canterbury.ac.nz> writes:

It's not clear exactly what you're after here. Are you trying to define the lowest-level interface upon which everything else will be built? If so, I think what you have presented is FAR too complex.

It seems to me you need only two things: ... t = tasklet(f) t.transfer() (Sorry if I missed something -- I've been way busy lately and haven't been giving this much attention -- that said...) But (if I understand the current plan) we will need mechanisms internal to the Python interpreter to transfer values and maintain blocked/running state anyway; since when you generate a tasklet and run it: t = tasklet(f) t.transfer() That may cause many more tasklets to be generated, run, and destroyed that you don't ever see ... recursions/function calls in f, and only-Christian-knows what else... so the transfer value mechanism might as well be built in.

I think all these little things are cheap to implement.

I haven't thought enough about the "unamed produce-and-continue function" to decide how exactly it should work.

Somebody named it "resume", and together with "suspend" we get a nice couple. On the other hand: I'm not sure whether resume should block its caller. I'm very undecided after all the input I got, if it is in fact better to forget data transfer completely by now and just make switching primitives which always work.

I have two concerns in implementing uthreads this way (scheduler in C):

1 -- there doesn't seem to be anyway to "kill" a tasklet

Not yet, but I want to provide an exception to kill tasklets. Also it will be prossible to just pick it off and drop it, but I'm a little concerned about the C stack inside. This might be the last resort if the exception doesn't work.

2 -- the scheduling algorithm will be hard to tune (we'll probably at least need tasklet priority...) Maybe there should still be a "timeslice" function so an in-Python scheduler can be written?

We had the timeslice function, yes. I think to make things simpler this time and just periodically call the scheduler which is written in C. I also have a rough concept of priorities which can be very cheaply implemented. Maybe I implement some default behavior, but allow these objects to be subclassed from Python?

ciao - chris

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