Re: How to do a callback sort of thing with pyAmf

> Hi Mike:
>
> --- On Tue, 5/12/09, Mike Dickson <mike.dickson@...> wrote:
>
>
> > Is there a well known pattern for handling a case where a client
> > should get notified when the state of a server/remote object
> > changes? I figure I can make the client make a remote call that blocks
> > on a condition variable in my server and wake it up when the data changes
> > but that means a thread per client and I don't like how that
> > scales?
>
> Since I left my last gig, I haven't played with PyAMF. So here goes....
>
> Like the Observer design pattern?
>
> If I understand you correctly, perhaps you can poll the remote site with  task.loopingCall(). If the loopingCall function detects a change,
> it can create a Deferred and start the processing by doing a callback.
> This way you are not creating threads.
>
> pseudo code
>
> """
> my application logic is in here
> """
> def doSomething(result):
>     .....
>
> """
> your polling/state change logic is here
>
> """
>
> def poll():
>     state = yield client.getPage(...)   #short-hand, an inlineCallback
>     if state != oldState:
>        oldState = state
>        deferred = defer.Deferred().addCallback(doSomething)
>        deferred.callback(result)   # start the processing right away  
>
> in startup code
>  
> task = tasking.loopingCall(poll)
> task.start(.01)
>
>
> > Mike (wishing python had continuations)
>
> You could use Stackless Python. About a year ago, I posted examples of how to use PyAMF with Stackless. Shameless plug: I also presented a talk at Pycon 2008 "Adventures in Stackless Python Twisted Integration."
>
> Cheers,
> Andrew
>