Thanks for the help on this everyone
Tim Hughes mailto:thug...@thegoldfish.org Without religion, people wouldn't pray for peace, they would work towards it. On Fri, Apr 24, 2009 at 8:33 PM, Drew Smathers <drew.smath...@gmail.com>wrote: > On Fri, Apr 24, 2009 at 2:28 AM, Nathan <nathan.sto...@gmail.com> wrote: > > On Thu, Apr 23, 2009 at 9:34 PM, Tim Allen <t...@commsecure.com.au> > wrote: > >> Tim Hughes <thug...@thegoldfish.org> wrote: > >>> Am I completly missing the point here or is there something incorrect > with > >>> my code. > >> > >> Yes, it seems you have missed the point somewhere. > >> > >>> def blocking_method(self, duration=5): > >>> """block the instance for a specified duration""" > >>> started = time.asctime() > >>> time.sleep(duration) > >>> data = "I started at %s and i slept %d seconds then woke at %s" > % > >>> (started, duration, time.asctime()) > >>> return data > >> > >>> def blocking_method_fixed(self, duration=5): > >>> d = Deferred() > >>> d.callback(self.blocking_method(duration)) > >>> return d > >> > >> Your blocking_method_fixed() wraps the result of blocking_method() in a > >> Deferred, but it doesn't actually do anything to prevent > >> blocking_method() from blocking. Deferreds have no magical ability to > >> prevent things from blocking on their own, they are just a tool you can > >> use to handle some of the control-flow issues that arise when writing > >> non-blocking code. > >> > >> For example, here's a method that does more or less what > >> blocking_method() does, but in a non-blocking manner: > >> > >> def non_blocking_method(self, duration=5): > >> started = time.asctime() > >> d = Deferred() > >> reactor.callLater(duration, d.callback, None) > >> > >> def do_stuff_after_timeout(result): > >> # Here, 'result' will contain the None we passed to > >> # callLater > >> data = "I started at %s and I slept %d seconds then woke " \ > >> "at %s" % (started, duration, time.asctime()) > >> return data > >> d.addCallback(do_stuff_after_timeout) > >> return d > >> > >> See how the method does some initial preparation, then schedules a > >> callback to be run after the long-running operation has completed. > >> > >> If you have a long-running network call to do instead of a simple > >> sleep, there's probably a Twisted API or addon that will perform the > >> call and give you back a Deferred, rather than blocking until it has an > >> answer. If you're trying to use a third-party client library that > >> doesn't offer a non-blocking API, about the only thing you can do is > >> call that API in a thread, using the reactor.callInThread() method (but > >> note that Twisted is not thread-safe, so the thing you call in a thread > >> can't use any of Twisted's functionality except via > >> reactor.callFromThread()) > > > > The above email makes a great FAQ item, IMO. I know there's already > > docs covering this, but this issue comes up soooo many times (it took > > me a month to wrap my head around it initially) that it wouldn't hurt > > to hit the issue from many directions in many styles. > > > > It is one of the FAQ items: > > > http://twistedmatrix.com/trac/wiki/FrequentlyAskedQuestions#HowdoIuseDeferredstomakemyblockingcodenon-blocking > > Apparently there's also been some stitchwork done to commemorate this. > > -Drew > > _______________________________________________ > Twisted-Python mailing list > Twisted-Python@twistedmatrix.com > http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python >
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