Re: Threading on win32

Hugo Hallqvist wrote:
> Hello everyone,
>
> I've recently had reason to investigate how to do asynchronous
> notification from worker-threads to a main-thread (which handles all
> gtk related function calls). After searching the web and mailing-lists
> for pygtk for examples on this topic I found out about the following
> possibilities:
>
> 1. Using gobject.io_add_watch() to watch a filehandle for activity.
> There are several variations on this one:
> 1.1 Use a temporary file. (Doesn't work on windows.)
> 1.2 Use a AF_INET socket. (Does work on windows, but many "personal
> firewalls" get suspicious about it, so an alternative solution is
> probably preferred.)
> 1.3  Use os.pipe(). (This uses an extra thread per fd, due to glib's
> gio_channel stuff, but otherwise should work fine.)
> 2. Lock the gdk-lock inside worker-thread and schedule an function to
> be called within main-thread using gobject.idle_add() .
> 3. Use the gsource-module to make pygtk able to listen to a win32
> event. It can be found here:
> http://www.daa.com.au/pipermail/pygtk/2004-February/006961.html
> I have briefly tested this technique, but didn't get it to work
> reliably. This otherwise seems like a very good solution.
>
> I've written a test-program which shows the points 2 and 1.3.  Both
> work fine on my linux installation (debian unstable, python 2.3.5,
> pygtk 2.4.1), however the example using pipes hangs when run in
> windows (windows xp, python 2.3.4, pygtk 2.4.1).
>
> Anyway, I've found a solution (point 2) which works reliably for me.
> Maybe it would be good to document that it is not possible to use
> os.pipe() with the gobject.io_add_watch() function on windows.
>
> Any alternative solutions to the original problem apart from the ones
> listed above would be greatly appreciated.

I think that gobject.idle_add is the simplest solution, and AFAIK you 
don't need to enter the gdk lock to call it.  Note that you do need to 
enter the gdk lock inside the idle function if you are doing gui stuff 
in it.

If you're using Python 2.4, you can wrap it up as a decorator.  The 
following code is untesed, and probably gratuitous :-)

    def idlefunction(function):
        def in_idle(args, kw):
            gtk.threads_enter()
            try:
                function(*args, **kw)
                return False
            finally:
                gtk.threads_leave()
        def wrapper(*args, **kw):
            gobject.idle_add(in_idle, args, kw)
        return wrapper

    @idlefunction
    def show_message(message):
        w = gtk.Window()
        w.add(gtk.Label(message))
        w.show_all()

--
Tim Evans
Applied Research Associates NZ
http://www.aranz.com/
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