[py]inotify, polling, gtk and gio

i have this software with a gtk mainloop, using dbus and all that fun stuff that seems to play together nicely. i know about the kernel inotify support, and i wanted it to get integrated with that above stack. i thought i was supposed to do it with pyinotify and io_add_watch, but on closer inspection into the pyinotify code it turns out that it seems to actually use polling! (search for: select.poll)

thinking i was confused, i emailed a friend to see if he could confirm my suspicions. we both weren’t 100% sure, a little searching later i was convinced when i found this blog posting. i’m surprised i didn’t find out about this sooner. in any case, my application seems to be happy now.

as a random side effect, it seems that when a file is written, i still see the G_FILE_MONITOR_EVENT_ATTRIBUTE_CHANGED *after* the G_FILE_MONITOR_EVENT_CHANGES_DONE_HINT event, which i would have expected to always come last. maybe this is a bug, or maybe this is something magical that $EDITOR is doing- in any case it doesn’t affect me, i just wasn’t sure if it was a bug or not. to make it harder, different editors save the file in different ways. gedit seems to first delete the file, and then create it again– or at least from what i see in the gio debug.

the code i’m using to test all this is:

#!/usr/bin/python
import gtk
import gio
count = 0
def file_changed(monitor, file, unknown, event):
  global count
  print 'debug: %d' % count
  count = count + 1
  print 'm: %s' % monitor
  print 'f: %s' % file
  print 'u: %s' % unknown
  print 'e: %s' % event
  if event == gio.FILE_MONITOR_EVENT_CHANGES_DONE_HINT:
    print "file finished changing"
  print '#'*79
  print 'n'
myfile = gio.File('/tmp/gio')
monitor = myfile.monitor_file()
monitor.connect("changed", file_changed)
gtk.main()

(very similar to the aforementioned blog post)

and if you want to see how i’m using it in the particular app, the latest version of evanescent is now available. (look inside of evanescent-client.py)

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logging out of $SESSION

the software (evanescent) that i’m working on is supposed to log out the user from its current X session. originally i had some yucky looking code that ran a kill on gnome-session, which quickly got replaced with:

os.system('gnome-session-save --logout-dialog')

i’ve decided this was still a little crufty, so i’ve recently replaced this with:

bus = dbus.SessionBus()
remote_object = bus.get_object('org.gnome.SessionManager', '/org/gnome/SessionManager')
# specify the dbus_interface in each call
remote_object.Logout(0, dbus_interface='org.gnome.SessionManager')
# or create an Interface wrapper for the remote object
#iface = dbus.Interface(remote_object, 'org.gnome.SessionManager')
#iface.Logout(0)
# introspection is automatically supported
#print remote_object.Introspect(dbus_interface='org.freedesktop.DBus.Introspectable')

documentation can be found, although it took a little digging. the only catch is that this is gnome specific, and you need different code for kde, and each other DE. thanks to http://www.purinchu.net/wp/2009/06/12/oh-fun/ for the kde version of the above.

help! please contribute information on making this work on other platforms, and/or how to detect which platform is running. at the moment my ugly solution is:

if os.name == 'nt': return 'windows'
elif os.getenv('KDE_FULL_SESSION') == 'true': return 'kde'
elif os.getenv('GNOME_DESKTOP_SESSION_ID') != '': return 'gnome'
else: return ''

hth

ps: i’m unable to indent code in wordpress (i’m sure it’s my fault somehow) so the above code was trimmed to give you the right idea, without being complete. leave a message if you want some source files.