[Twisted-Python] Chaining deferreds - Twisted+PyGtk

Jean-Paul Calderone exarkun at divmod.com
Wed Jul 15 21:14:46 EDT 2009

On Thu, 16 Jul 2009 00:36:33 +0200, Łukasz Rekucki <lrekucki at gmail.com> wrote:
>I'm writing a simple chat client using twisted and pygtk. I have a problem
>with a chained deferred not being continued. Here is my call chain:
>* MyProtocol.dataReceived -> fires a predefined Deferred [call it A]
>* A.callback1 -> creates a new Deferred B, adds a single callback to it,
>displays a GtkDialog returns B
>* [A stops]
>* dialog exits, I call B.callback(result_id) from the signal callback
>* all callback in B's chains are called
>* program hangs instead calling A.callback2
>Is this a thread related problem ? Am I doing something terribly wrong by
>calling a deferred from the gtk thread ?

It sounds like you're doing the right thing.  There is no gtk thread when you
use one of the gtk integration reactors - gtk and Twisted coexist in the same
thread.  So it's just fine to use Twisted APIs from a gtk signal callback.

Perhaps there is an unexpected error occurring.  Do you have a final errback
on your Deferred (one on A in this case would be fine) which logs the error
or otherwise makes it visible?  If not, you have to rely on luck and the
garbage collector to make this report.


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