cups-browsed uses GMainLoop and global variables, how to introduce locks against race conditions?

[Ted Gould]

On Wed, 2016-12-07 at 17:39 -0200, Till Kamppeter wrote:
> On 12/02/2016 04:13 PM, Till Kamppeter wrote:
> > The way how cups-browsed works is the following:
> > 
> > First, a GMainLoop is created:
> > 
> > gmainloop = g_main_loop_new (NULL, FALSE);
> > 
> > Browsing for legacy CUPS broadcasts is attached to the mail loop
> > via
> > 
> >     GIOChannel *browse_channel = g_io_channel_unix_new
> > (browsesocket);
> >     g_io_channel_set_close_on_unref (browse_channel, FALSE);
> >     g_io_add_watch (browse_channel, G_IO_IN, process_browse_data,
> > NULL);
> > 
> > Many other things are added via
> > 
> > g_idle_add ()
> > 
> > and
> > 
> > g_timeout_add_seconds ()
> > 
> > Reaction to D-Bus notifications is added via the
> > 
> > g_signal_connect()
> > 
> > function.
> > 
> > Avahi browsing is set up with these calls
> > 
> >     /* Allocate main loop object */
> >     if (!glib_poll)
> >       if (!(glib_poll = avahi_glib_poll_new(NULL,
> > G_PRIORITY_DEFAULT)))
> >       {
> >     debug_printf("ERROR: Failed to create glib poll object.\n");
> >     goto avahi_init_fail;
> >       }
> > 
> >     /* Allocate a new client */
> >     if (!client)
> >       client = avahi_client_new(avahi_glib_poll_get(glib_poll),
> >                 AVAHI_CLIENT_NO_FAIL,
> >                 client_callback, NULL, &error);
> > 
> >     /* Check wether creating the client object succeeded */
> >     if (!client) {
> >       debug_printf("ERROR: Failed to create client: %s\n",
> >            avahi_strerror(error));
> >       goto avahi_init_fail;
> >     }
> > 
> > Strange is that this Avahi browsing setup is done before creation
> > of the
> > main loop. Also some g_timeout_add_seconds () calls are done before
> > creating the main loop.
> > 
> > After that, the main loop gets started via
> > 
> > g_main_loop_run (gmainloop);
> > 
> > My questions are now:
> > 
> > - Is this way everything attached to the main loop?
> > 
> > - Do I have to do function calls in the beginning and in the end of
> > each
> > callback function to acquire and release a lock? Which ones?
> > 
> > - If something of this is not attached to the main loop, how do I
> > attach
> > it?
> > 
> > I do not explicitly start any new threads.
> > 
> >    Till
> > 
> No one has any idea to help me here?
If there are no threads, then there isn't any locking needed on the
data structure, so it's probably something else that is causing your
problem. But you're probably out of mailing list territory at this
point, need a way to recreate and to find someone who has time to look
through the code.
Ted
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