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
