[Twisted-Python] xmlrpc - Possable failure to understand async concept
thughes at thegoldfish.org
Sun Apr 26 17:23:11 EDT 2009
Thanks for the help on this everyone
mailto:thughes at thegoldfish.org
Without religion, people wouldn't pray for peace, they would work towards
On Fri, Apr 24, 2009 at 8:33 PM, Drew Smathers <drew.smathers at gmail.com>wrote:
> On Fri, Apr 24, 2009 at 2:28 AM, Nathan <nathan.stocks at gmail.com> wrote:
> > On Thu, Apr 23, 2009 at 9:34 PM, Tim Allen <tim at commsecure.com.au>
> >> Tim Hughes <thughes at thegoldfish.org> wrote:
> >>> Am I completly missing the point here or is there something incorrect
> >>> 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:
> Apparently there's also been some stitchwork done to commemorate this.
> Twisted-Python mailing list
> Twisted-Python at twistedmatrix.com
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