Re: C-thread calling Python

[Richard Procter <richard n procter gmail com>]

Hi Matthias, 

I have held off replying in case someone more knowledgeable might 
step in here; I have only dipped my toes into threading on 
python/pygobject; below are some reflections to take with a grain of salt. 

> Date: Tue, 17 Jan 2012 12:31:43 +0100
> From: Matthias Vogelgesang <matthias vogelgesang gmail com>
> Subject: Re: python-hackers-list Digest, Vol 21, Issue 2
> [snip] 
> I do it rather similarly but as I am building a pure GLib app from
> GObject-based library, I don't have any Gtk dependencies and therefore
> the Gtk main loop is not helping. I will just sketch, how it is done
> now (Foo is the GObject-based library written in C):
> 
> from gi.repository import Foo, GObject
> 
> class MyFilter(Foo.Filter):
>    def do_process(self, data):
>        print data
> 
> if __name__ == '__main__':
>    GObject.threads_init()
>    f = MyFilter()
>    caller = Foo.Caller()
>    caller.call(f, None)
> 
> foo_caller_call() basically creates a thread that calls the
> foo_filter_process() method of the passed object and joins this
> thread. If I don't create a thread but just call foo_filter_process()
> from foo_caller_call() everything works fine and the Python code is
> executed.

If Foo.Caller.call() is purely GLib then it is presumably not creating 
threads using the python API. These require care to execute safely within
the python interpreter [1]. I note though that my code-generated GTK+2 
pygobject wrappers supply this in the C method proxies that call into a python 
subclass of a wrapped gobject. 

Are you saying that do_process() is never executed if you call it from 
the C-level in a newly created non-python thread? It may be worth 
while determining exactly where the call stalls to test the presumption 
that the C-level code is blocking trying to acquire the GIL before executing 
do_process(). 

Without more detail I can't be more specific. I've never done what you are doing 
but, at least conceptually, I see no reason why it cannot work. I can't afford 
the time to reply further I'm afraid. 

warm regards, 
Richard. 

[1] http://docs.python.org/c-api/init.html#non-python-created-threads