[Twisted-Python] Some things I've learned: safer callbacks, better t.p.context

[Amber "Hawkie" Brown]

> On 20 Oct. 2016, at 08:54, Glyph Lefkowitz <glyph at twistedmatrix.com> wrote:
> 
> 
>> On Oct 19, 2016, at 2:47 PM, Itamar Turner-Trauring <itamar at itamarst.org <mailto:itamar at itamarst.org>> wrote:
>> 
>> On Wed, Oct 19, 2016, at 05:45 PM, Itamar Turner-Trauring wrote:
>>> Well... I had a test that went through synchronous Deferred path. And yeah, it was easier to write than async test. But it failed to catch a bug that was only in async case. So the problem I see is that supporting both in Deferred means you need twice the number of tests each time you use Deferreds.
>> 
>> Er, that was unclear. I had a bug that wasn't caught by tests because it passed with sync Deferred and failed with async Deferred callback, and I didn't have tests for latter.
> 
> 
> To be clear: I do see this as a downside to Deferred's architecture; it's a tradeoff.  I see the loose coupling with the event loop as a worthwhile upside.

One thing that I have still not figured out is how Futures (which are tightly tied to an event loop) will possibly ever work over multiple event loops. I think since you can't really chain them, this is less of a problem, but Deferreds like to absorb other Deferreds and make one big one, which would make the tight coupling problematic if you wanted to use two event loops (like, say, a GTK one and an IOCP one on Windows).

- Amber

> 
> However, it's totally possible to write the async Deferred callback case as well, just by having the test fire the Deferred after returning to the test body instead of firing it before :-).
> 
> -glyph
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