[Python-ideas] The async API of the future

Jasper St. Pierre jstpierre at mecheye.net
Sat Oct 20 02:50:00 CEST 2012

On Fri, Oct 19, 2012 at 8:33 PM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:

... snip ...

> That's another thing that worries me. With a ready-based
> event loop, this is fairly straightforward. If you can get
> hold of the file descriptor or handle that the GUI is
> ultimately reading its input from, all you need to do is
> add it as an event source to your main loop, and when it's
> ready, tell the GUI event loop to run itself once.

For most windowing systems, this isn't true. You need to call some
function to check if you have events pending. For X11, this is
"XPending". For Win32, this is "GetQueueStatus".

But overall, the thing is that most GUI libraries have their own event
loops. In GTK+, this is done with a "GSource", which can have support
for custom sources (which is how the calls to the above APIs are
made). What Twisted does is this case is swap out their own select
loop with another implementation built around GLib's GMainLoop, which
uses whatever internally.

I'd highly recommend taking Twisted's approach of having swappable event loops.

The question then becomes how you swap out the main loop: Twisted does
this with a global reactor which you "install", which the community
has found rather ugly, but there isn't really a better solution
they've come up with. They've had a few proposals over the years to
add better functionality, so I'd like to hear their experience on

> --
> Greg
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