[Stackless] Questions about the Tasklet _channel attribute

Andrew Francis andrewfr_ice at yahoo.com
Sat Aug 30 19:20:31 CEST 2008

Hi Christian:

--- On Fri, 8/29/08, Christian Tismer <tismer at stackless.com> wrote:

> For some reason, this is something I always tried to
> prevend.
> The channel logic is not meant to be manipulated.
> If this is possible via pickling, then it is considered a
> bug.

I have included some sample code illustrating attaching and detaching tasklets to and from channels. It involves __reduce__()
and __setState__ as per the instructions on the Stackless wiki. Christian, is it stuff like this that you have objections? 

That said, I believe that the ability to detach a tasklet blocked on a channel and reattaching it to a new channel is a useful feature. It opens up possibilities like process migration and swapping out of memory groups of tasklets that have been waiting a long time for I/O. The later is of particular use to me.

Since I have more time, I will write more useful examples of this feature in the weeks to come.


Andrew Francis
<song>Jeremy - Pearl Jam </song>

The purpose of this programme is to illustrate how tasklets can
be attached an detached from channels 

import stackless

def detach(channel, tasklet):
     x, y, (balance, flags, tasklets) = channel.__reduce__()
     channel.__setstate__((balance, flags, tasklets))
     return channel

def attach(channel, tasklet):
     x, y, (balance, flags, tasklets) = channel.__reduce__()
     channel.__setstate__((balance, flags, tasklets))
     return channel

class Process(object):
    def __init__(self, channel): 
        self.channel = channel

    def execute(self):
        print "my channel:", self.channel
        print self.channel.receive()

if __name__ == "__main__":
     channel1 = stackless.channel()
     channel2 = stackless.channel()

     p = Process(channel1)
     t = stackless.tasklet(p.execute)()

     channel1 = detach(channel1, t)
     p.channel = channel2 = attach(channel2, t)


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