[Twisted-Python] Event Driven Programming 101 question
sflist at ihonk.com
Sat Aug 2 06:37:00 EDT 2003
I've got a few questions about Deferreds. I understand the concept better, but
I need a little help at the moment. It's apparent to me that a lot's going on
behind the scenes between Deferreds and the Reactor, and that
twisted.enterprise orchestrates things in a way I don't yet understand.
I'm looking at this from the perspective of my little XML-RPC server. A client
hits a XML-RPC function, and by the time that function returns its value, it
needs all its Deferreds to have generated their results. That leads to this
When is a Deferred guaranteed to have a result?
One answer could be, "When its callback gets called." And that would be true.
But what if the function that gets the Deferred needs the result before it
can move on? It seems like it'll get the Deferred and then go on its merry
way, whether the Deferred has a result or not. And that's confusing to me,
because I'm left wondering what happens if my database takes a long time to
result = dbpool.runQuery("select * from gigantic_table") # adbapi
In this case, what's it gonna be? A Deferred that's evaluated as None because
Postgres is still churning, or is Twisted only going to let the code continue
once the Deferred has a result?
Sorry if it seems I'm not making sense... Event-driven programming is new to
me, but I'm a motivated learner. :-) (And if anybody knows of a good general
guide to this paradigm, I'm all ears.)
Thanks for your help!
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