[PEAK] More event questions

[Chad Rosenberg]

What I've got is a method compiled by a cheetah script.  This method is
called as the result of a Twisted callback.  The cheetah method needs to
be able to make a PB call to fetch some data and block until the data
arrives.  Something like this:

-----------
  def twistedCallback(self):
      self.callCheetahCompiledMethod()

  ...

  def cheetahCompiledMethod(self):
      ...
      print self.utilClass.lookup(foo)

  ...

class UtilClass(binding.Component):
  def lookup(self, whatToLookup):
      pbDeferred = self.pbCall(whatToLookup)
      # Some way to block until results are gotten
      return results
-----------

"cheetahCompiledMethod", itself, cannot be asynchronous or use callbacks.
The call to "lookup" can't be done before "cheetahCompiledMethod" is
called since it is unknown at that time what "cheetahCompiledMethod" will
require.  The reason I kept trying to get runUntil to work is it seemed,
at the time, like a logical choice to block on the PB call in "lookup".
My heart is not set on nested event loops, but I have yet to figure out
a way to get the above to work otherwise.  :(

  - Chad

On Fri, 12 Nov 2004, Phillip J. Eby wrote:

> At 03:26 PM 11/11/04 -0800, Chad Rosenberg wrote:
>
> >Is it safe to use runUntil from a call originating from reactor.callLater?
>
> Not with the same reactor instance.
>
>
> >I thought this would eliminate nested runUntils, but I am still getting
> >Unexpected reactor exits.  Any insights?
>
> Yes.  Stop using runUntil().  I haven't seen any examples or explanations
> from you that show you actually need it for anything.  'runUntil()' is
> intended for a top-level event loop.  Code that is inside an event loop
> should not use it unless you need a nested event loop.  If you can explain
> why you need a nested event loop, I'll help you figure out how to get it
> accomplished.
>
> Most likely, however, whatever you're trying to do will more easily be
> accomplished by yielding to an event, or setting an event callback.
>
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