[Twisted-Python] Non returning deferred result.

Fri Apr 18 00:48:20 MDT 2008

Just a quick update. Doing a "reactor.iterate()" after the callback
fixed the behavoir. ie.

--------
deferred.callback( http.Response(responsecode.OK,
				{'content-type': http_headers.MimeType('text', 'html')},
				"Success!" ) )
reactor.iterate()
--------

so my new question is, is this the best way to do this? Is there a
better way? Also is reactor.iterate() threadsafe? Are there potential
problems callinf reactor.iterate() from a thread spawned off the running
reactor thread?

Kind Regards

Crispin Wellington
<cwellington at ccg.murdoch.edu.au>

On Fri, 2008-04-18 at 06:35 +0000, Crispin Wellington wrote:
> Hey everyone,
> 
> Sorry about the subject line, its a difficult problem to sum up in a
> single line subject. Give me a little time to explain.
> 
> I'm using twisted.web2. I have a generic webservice over http. It
> receives a file via standard POST http upload. It saves this to disk
> using non blocking stream setup as outlines in web2.static.FileServer.
> 
> Now I don't immediately return a response, because another thread then
> processes this file and builds an output file. So I return a deferred
> from my render() function. When the output file is finished building,
> the deferred callback is triggered with the http.Response() object and
> the response is finally returned to the waiting http connection.
> 
> This DOES work except for a little strange behavoir. When the deferred
> callback is triggered, the client doesn't see any response, the
> connection just stays open. Then if I connect to the webservices from
> anywhere, even a bad URL, I get my response suddenly back.
> 
> It's as if the callback is not triggered until some TCP activity cause
> the main reactor to pump the pending requests or something. Is there
> anyway to get this deferred callback to be recognised and processed
> immediately? I could do a kind of hack, where the deferred callback is
> called, and then a quick connection is made to the webservice to "pump"
> the message through, but it doesn't seem very 'right' to me.
> 
> Heres some summary of the approach incase the devil is in the details...
> 
> My Resource class:
> ==================
> class UploadFile(resource.PostableResource):
> 	# 1 gig is max file upload size
> 	maxSize=1 * 1024 * 1024 * 1024
> 	
> 	def render(self, ctx):
> 		"""Create the job for this upload and return the relevent deferred"""
> 		request = iweb.IRequest(ctx)
> 		
> 		job=Job()
> 		deferred = job.SubmitInput(request.files)				
> 		
> 		return deferred
> 		
> 
> My deferred callback:
> =====================
> deferred.callback( http.Response(responsecode.OK,
> 				{'content-type': http_headers.MimeType('text', 'html')},
> 				"Success!" ) )
> 
> My TopLevel:
> ============
> class Toplevel(resource.PostableResource):
> 	addSlash = True
> 	def render(self, ctx):
> 		return http.Response(responsecode.OK,
> 				{'content-type':
> 						http_headers.MimeType('text', 'html')},
> 						"""
> <html>
>     <form action="http://localhost:8080/uploadfile"
>             enctype="multipart/form-data"
>             method="post">
>         filename: <input type="file" name="filename">
> 		filename2: <input type="file" name="filename2">
>         <input type="submit" value="submit">
>     </form>
> </html>
> """)
> 	child_upload = UploadFile(jobqueue)
> 
> 
> My server startup:
> ==================
> # Create the resource we will be serving
> test = Toplevel()
> 
> # Setup default common access logging
> res = log.LogWrapperResource(test)
> log.DefaultCommonAccessLoggingObserver().start()
> 
> # Create the site and application objects
> site = server.Site(res)
> application = service.Application("demo")
> 
> # Serve it via standard HTTP on port 8080
> s = strports.service('tcp:8080', channel.HTTPFactory(site))
> s.setServiceParent(application)
> 
> 
> 
> 
> Im running the application as:
> 
> twistd -noy server.py
> 
> 
> 
> Twisted v8.0.1+, actually, the lastest SVN head.
> 
> Any one with more knowledge of twisted's internals have any ideas on
> what is happening? Does anyone have any good ideas on how to make the
> deferred callback trigger an immediate response (without opening a new
> TCP connection to kick it into gear)?
> 
> 
> Thanks
> 
> Regards
> Crispin Wellington
> <cwellington at ccg.murdoch.edu.au>
> 
> 
> 
> 
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