[Python-Dev] Twisted Isn't Specific (was Re: Trial balloon: microthreads library in stdlib) (original) (raw)

Larry Hastings larry at hastings.org
Thu Feb 15 18:48:47 CET 2007

Martin v. Löwis wrote:

Now, for these generalized event loops, it may not be possible anymore to combine all event sources into a single blocking call.

Right, that's why my proposal assumed that each disparate event source would need its own thread.

Ah, threads :-( It turns out that you need to invoke GetMessage in the context of the thread in which the window was created. In a different thread, you won't get any messages.

Oof! I'm embarrassed to have forgotten that. But that's not a fatal problem. It means that on Windows the PerfectReactor must service the blocking GetMessage loop, and these other threads notify the PerfectReactor of new events by sending a message. (Either that, or, it could poll GetMessage and its incoming event queue without ever blocking. But that is obviously suboptimal.) I think I've done this sort of thing before, in fact.

Of course, in the absence of any windows, the Windows PerfectReactor could fall back to a mutex. Abstract this inside PerfectReactor and its event sources wouldn't notice the difference.

Integrating with threads might be a solution in some cases, and a problem in others. You can't assume it is a universal solution.

Universal? Yeah, I doubt it too. But perhaps it would be "good enough for nearly all cases". In the cases where it wasn't, it could throw an "I can't listen to that type of event right now" exception, forcing you to fall back to preconfiguring your central reactor by hand.

Anyway, like many folks I'm hoping this whole conversation results in establishing basic standard duck-typed conventions--what other languages might call "interfaces"--for event senders and receivers. In which case this non-universal threaded approach would simply be one of several to choose from.

I'd be interested to hear about other situations where threading would cause a problem. My suspicion is that Windows is the hard one, and as I've shown that one is solvable.

Thanks for the thoughtful reply,

/larry/

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