On 8 Nov 2009, at 02:33, Antoine Pitrou wrote:
Hello,
They do seem specialized for continuation-passing style programming
though. As far as I can tell from the docs
(http://python.net/crew/mwh/apidocs/twisted.internet.defer.Deferred.html
), the only way to process the results of a Deferred is my installing
a callback.
Yes, but the last callback in the chain could trigger an Event, a
Queue
or any other synchronization object to which you could wait on, if you
want something "synchronous" (despite the title of your original
message: "asynchronous execution" :-)).
Touché ;-) But I was actually indenting this to be used for
applications that are organized for synchronous but need some extra
performance for a few method calls.
with ThreadedDeferredMaker(max_threads=5) as dm
deferreds = []
for url in URLS:
deferred = dm.defer(load_url, url)
deferred. addCallbacks(print_success, print_failure, url=url)
deferred.unpause()
deferreds.append(deferred)
If you have a bunch of deferreds and want your callback to trigger
when
all deferreds are finished/failed, you can use a DeferredList. A
DeferredList is itself a Deferred so you can add callbacks to it
(including one which makes things synchronous as explained above).
http://twistedmatrix.com/documents/8.1.0/api/twisted.internet.defer.DeferredList.html
(note that, as the doc says, "that you can still use a Deferred after
putting it in a DeferredList". That is, you can react individually to
each result to implement e.g. a progress indicator, and also react to
the completion of all deferreds)
That's cool. A hybrid approach that allows you to use both callbacks
and inspection might make sense.
Cheers,
Brian
Of course an all-synchronous API is still simpler to use for the use
cases it is meant for.
Regards
Antoine.
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