[pygtk] UI will be blocked if creating a message dialog by emitting a signal

[Niklas Koep]

Emitting signals from a thread will run the handler in the same thread. You
shouldn't call gtk functions from a thread other than the main one. If you
insist on doing so you have to make sure to acquire the GDK lock first by
wrapping your code in gtk.gdk.threads_enter() ... gtk.gdk.threads_leave()
calls. In this case you also have to call gtk.gdk.thread_init() as
otherwise the main loop will never release the GDK lock. The easier
solution is to push the signal emission to the main thread by replacing
self.emit('ASignal') with gobject.idle_add(self.emit, 'ASignal') which
guarantees the handler will also run in the main thread (which already has
the GDK lock).

Regards.


On Thu, Jul 25, 2013 at 4:56 PM, Todong Ma <gbstack08 at gmail.com> wrote:

>  Hi, everyone
>
> I met a problem that UI will be blocked forever if I emit a signal from a
> thread to create a message dialog.
> Following code will reproduce the issue, please let me give a short
> explanation: AThread thread defines a custom signal named "ASignal", and
> the signal handler is aSignal() function of MainWindow class. The aSignal()
> function is used to display a message dialog. Emitting "ASignal" signal
> will display the message dialog successfully but the UI is blocked forever.
>
> import gtk
> import gobject
> import threading
>
> class AThread(threading.Thread, gobject.GObject):
>     __gsignals__ = {
>         'ASignal': (gobject.SIGNAL_RUN_LAST, gobject.TYPE_NONE, ())
>     }
>     def __init__(self):
>         threading.Thread.__init__(self)
>         gobject.GObject.__init__(self)
>
>     def run(self):
>         self.emit('ASignal')
>
> class MainWindow(gtk.Window):
>     def aSignal(self, obj):
>         dialog = gtk.MessageDialog(self, gtk.DIALOG_DESTROY_WITH_PARENT,
> gtk.MESSAGE_INFO, gtk.BUTTONS_CLOSE, 'asdfasf')
>         dialog.run()
>         dialog.destroy()
>
> gobject.threads_init()
>
> w = MainWindow()
>
> t = AThread()
> t.connect('ASignal', w.aSignal)
> t.start()
>
> gtk.main()
>
>
> Any suggestion is appreciated.
>
> Thanks,
>
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