[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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July 21, 2009
392 words

• technical