On 22 Μαρ 2012, at 12:34 μ.μ., Uri Okrent wrote: > On Thu, Mar 22, 2012 at 2:17 PM, Itamar Turner-Trauring > <ita...@itamarst.org> wrote: >> On 03/22/2012 08:05 AM, Uri Okrent wrote: >>> This implies that twisted can (and will) switch contexts from one >>> deferred to another even in the middle of execution of the first >>> deferred, correct? >> >> No. Deferreds are just slightly nicer callbacks. They have nothing to do >> with the event loop, or scheduling, or context switching. > > Maybe I should clarify my question: > > thing = 0 > def a(): > thing += 1 > thing += 1 > thing += 1 > thing += 1 > thing += 1 > > def b(): > thing = 0 > > def show_thing(): > print thing > > a.addCallback(show_thing) > b.addCallback(show_thing) > > given the two deferreds 'a' and 'b', with 'a' being called first, it > is possible for twisted to jump to 'b' in the middle of 'a' correct? > I.e., when show_thing runs after 'b' is finished it will always print > 0 because thing was set to 0 by 'b', but when show_thing runs as the > callback for 'a', it will print something between 0 and 5 and it is > non-deterministic, because 'b' may have jumped in at some point during > the execution of 'a' and reset 'thing' back to 0.
No, Twisted runs everything in a single thread, there's no way a callback can be interrupted. In the above case you will see either 5 or 0, nothing in between. (Nit - the above code will not compile or run, but I think your point made it across) > -- > Uri > > Please consider the environment before printing this message. > http://wwf.panda.org/savepaper/ > > _______________________________________________ > Twisted-Python mailing list > Twisted-Python@twistedmatrix.com > http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python _______________________________________________ Twisted-Python mailing list Twisted-Python@twistedmatrix.com http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python
