[Twisted-Python] Re: Transparent pooling of deferreds to be fired upon another

Andrew Francis andrewfr_ice at yahoo.com
Thu Apr 23 12:24:44 EDT 2009

Hi Terry:

--- On Thu, 4/23/09, twisted-python-request at twistedmatrix.com 

> Suppose I have a function called alertSupervisor that takes
> a string message for the supervisor and which returns a deferred. I
> want to be able to call that function from anywhere in my code, and I
> always want to get a deferred back, but if there's already a call in >progress to tell the supervisor the same thing then I don't want to bug >him/her by sending another message, but I do want to know when the >original >call fires.

Why can't you have the callbacks attached to the deferred, share a flag?

global flag

def callback(....):
    global flag
    if flag == False:
       flag = True
       # do body of function
       # don't do anything - flag have been previously fired

If I understand what is happening, this should work because of the non-preemptive nature of the reactor, that is you ought not get a race



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