[IronPython] Suspending, saving script execution?

Hogg, Jonathan Jonathan.Hogg at kbcaim.com
Mon Jan 29 01:01:39 PST 2007

Stackless Python is definitely the way to go, but if you needed to do
this in IronPython/.NET, you can get a poor man's form of
micro-threading with generators. Taking your example, you could re-write
it like so:
def main(self):
    yield move(5)
    yield turn(90)
    if self.direction == Direction.East:
        yield turn(180)
    yield move(2)

where 'move' and 'turn' are type constructors - or factory functions or
whatever - that return an object representing the action to be taken.
Now you instantiate the generator to create your micro-thread, and call
'.next()' on it to execute it up to the next yield.

t1 = mytank.main()
action = t1.next()

The difference between this and full threading is that it's cooperative
and that you have to write your own micro-thread scheduler. Presumably
you'll have some kind of game-state/event engine that will keep track of
what each of the actors is currently doing and when they become eligible
for execution again (it's finished moving/turning), you would poke them
to see what they want to do next.

Main problem is that if a piece of user-generated logic is badly behaved
(doesn't yield), then your game would hang.



From: users-bounces at lists.ironpython.com
[mailto:users-bounces at lists.ironpython.com] On Behalf Of Curt
Sent: 28 January 2007 17:37
To: Discussion of IronPython
Subject: Re: [IronPython] Suspending, saving script execution?

On 1/28/07, Erzengel des Lichtes <erzengel-von-licht at cox.net> wrote: 

	Now, the script is going to need to be suspended while it's
moving 5 meters
	(it's not going to teleport) forward, then again while it's
turning 90 
	degrees to the right, possibly again when it turns around, and
finally once
	again while moving forward 2 meters.
	I can't block the script without suspending the thread/fiber,
right? But
	with a large number of scriptable units, the system will not be
able to cope 
	with a thread/fiber per script.

This sounds like the sort of thing that Stackless Python[1] was invented
for.  This is a variation of CPython that -- by removing the dependency
of Python code execution on the processor's stack -- allows execution of
multiple objects without creating multiple threads.  The game "EVE
Online" uses Stackless Python for this purpose. 
I doubt you could accomplish something similar in IronPython simply
because of how the CLR works.  But the low-level hooks in CLR 2.0 that
were created for SQL Server may allow something in that direction.
1: http://www.stackless.com
2: http://www.eve-online.com
Curt Hagenlocher
curt at hagenlocher.org

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