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. ~ Nathan _______________________________________________ Twisted-Python mailing list Twisted-Python@twistedmatrix.com http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python
