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<TITLE>Re: [Twisted-Python] Newbie question: can't get getProcessOutput to run from inside a listenTCP service call-back</TITLE>
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<FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:14pt'>Hi Nick;<BR>
<BR>
Thanks for the answer. However, If I take the while loop out, “helloWorldTest()” returns immediately, and the Flex app gets the initial value of self.result. The defer.callback function doLog never gets called. If I call the “terminate()” from the Flex app, which in turn calls reactor.sop() the doLog function finally then gets called. I am looking for what I need to do to allow getProcessOutput to run such that the defer.callback function doLog actually gets called. <BR>
<BR>
I have figured out that if instead of calling getProcessOutput() directly within the helloWorldTest() method, that I can queue it for running after helloWorldTest() as returned, as in:<BR>
reactor.callLater(1, self. helloWorldTest2)<BR>
and that the defer.callback function doLog does then get called.<BR>
<BR>
This means that the defer.callback function doLog will get called after the helloWorldTest() has returned. I see can call helloWorldTest() , and then keep querying the python service from the Flex app until the defer.callback function doLog has run. <BR>
<BR>
I still don’t understand why calling getProcessOutput() directly within the helloWorldTest() method doesn’t work. Any explanation would be welcome.<BR>
<BR>
Thanks, Read Roberts<BR>
<BR>
On 10/17/09 1:53 AM, "Nick Joyce" <<a href="nick@boxdesign.co.uk">nick@boxdesign.co.uk</a>> wrote:<BR>
<BR>
</SPAN></FONT><BLOCKQUOTE><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:14pt'>On 17 Oct 2009, at 05:15, Read Roberts wrote:<BR>
<BR>
> I have a Python server using twisted which responds to pyAMF calls <BR>
> from<BR>
> Flex/Air applications (following Bruce Eckels 5/1/2008 article <BR>
> "Concurrency<BR>
> with Python, Twisted, and Flex"). The service is basically as <BR>
> follows below.<BR>
> When the client calls a service API, the API needs to make a OS <BR>
> shell call.<BR>
> I see that if I call reactor.stop() after the getProcessOutput call <BR>
> (such<BR>
> as within the doLog and doError functions), the call happens and I <BR>
> see the<BR>
> output. How can can I retrieve the output without calling <BR>
> reactor.stop()? In<BR>
> the example below, the AIR app calls the callback helloWorldTest(), <BR>
> and the<BR>
> deferred.addCallback function is never called.<BR>
><BR>
> import os<BR>
> from twisted.spread import pb<BR>
> from twisted.internet.utils import getProcessOutput<BR>
> from twisted.internet import reactor<BR>
><BR>
> class FlexInterface(pb.Root):<BR>
> def __init__(self):<BR>
> self.result e<BR>
><BR>
> def doLog(self, result):<BR>
> self.result = "%s" % (result)<BR>
> return result<BR>
><BR>
> def doError(self, failure):<BR>
> self.result = "%s" % ( failure)<BR>
> return failure<BR>
><BR>
> def helloWorldTest(self):<BR>
> deferred = getProcessOutput("echo", ["Hello World"], <BR>
> os.environ)<BR>
> deferred.addErrback(self.doError)<BR>
> deferred.addCallback(self.doLog)<BR>
> while (self.result == None)<BR>
> print "doLog still hasn't been called"<BR>
> return self.result<BR>
<BR>
<BR>
The while loop will block the event loop, preventing the deferred from <BR>
ever being called. PyAMF will accept a deferred as a return value for <BR>
the service function and will not return a response until the <BR>
deferred's callback is fired.<BR>
<BR>
So, you could re-write the method like:<BR>
<BR>
def helloWorldTest(self):<BR>
deferred = getProcessOutput("echo", ["Hello World"], <BR>
os.environ)<BR>
<BR>
deferred.addErrback(self.doError)<BR>
deferred.addCallback(self.doLog)<BR>
<BR>
return deferred<BR>
<BR>
If the deferred's callback is called then the return value of doLog <BR>
will be used as the response value. If the errback is called, the <BR>
return value of doError will be used as the response, in this case a <BR>
Failure instance. PyAMF converts Failure instances to remoting/<BR>
messaging error objects automagically, so the faultHandler on the <BR>
flash/air side will be called.<BR>
<BR>
hth,<BR>
<BR>
Nick<BR>
<BR>
<BR>
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