Re: Can g_file_monitor_file () report events from before it was created?

[Peter Clifton <pcjc2 cam ac uk>]

On Tue, 2011-09-06 at 01:42 +0100, Peter Clifton wrote:
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> Hi,
>
> I'm working on some code to monitor for file changes in our application,
> and ran into a bit of a problem today with the Save-As case.
>
> The order of operations is something like:
>
> 1. File monitor exists on the document file which was loaded last
> 2. User hits File->Save as.. (and enters a filename)

^__ Just as an interesting (and probably critical note), I don't see
this bug if I hard-code a Save-as filename.

I only get unexpected file-monitor events if I use a
gtk_file_chooser_dialog to select the new filename to save into.

I'm presuming that this dialog (or some IO plugin) may use
g_file_monitor, or threads, or SOMETHING - which is causing issues with
my own usage of g_file_monitor.

If anyone could help shed some light on this, it would be much
apprecaited.


> 3. Core of app saves file into the new file name
> 4. File monitor does not fire, as the saved file is not the one being monit=
> ored
> 5. Core of app notifies the GUI (with the file monitor) that the document w=
> e should be watching is now in the new filename.
> 6. g_object_unref() the old file monitor
> 7. Create new file monitor on the new file.
>
> After this happens, I actually get a change event fire from the new file
> monitor - despite the changes having been saved by the app's core
> (fopen / fclose directly to the file in question), before I even created
> the file monitor.
>
> Is it possible that Glib / GIO is caching some state incorrectly, and
> spotting on-disk changes from _before_ I created the file monitor, or is
> it more likely that the file doesn't "hit the disk" until some time
> after I fclose() it - and that it spots the change at this point in
> time?
>
> Any ideas what I might be doing wrong here?
>
> (PS. I got the feeling GLib / GIO is using polling, not anything clever
> like inotify to spot changes - is this correct?)
>
> Best regards,

-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)
Tel: +44 (0)1223 748328 - (Shared lab phone, ask for me)