Glib::Dispatcher: How to use a non-void signal for tunneling?

[Matthias Kaeppler <matthias finitestate org>]

Hi,

I need to update the GUI from outside the Gtk main thread. I wasn't 
happy with all the gdk_threads functions so I tried to incorporate 
Glib::Dispatcher in order to create a thread tunnel whenever I need to 
modify the GUI in another thread.

However, Glib::Dispatcher emits a sigc::signal<void>, but I need it to 
pass information around everytime an update is required. I especially 
can't use sigc::bind, since the information is updated everytime the 
update occurs (and this means it's probably a new object which is passed 
around on each call).

Here is the situation:
I am tranferring files asynchronously and display progress information 
in a Gtk::Dialog. The progress information object is handed to me in a 
signal handler which is called by Async::Handle::transfer. To visualize 
this information in the Dialog, I would have to pass this info object 
further through the thread tunnel in order to use it to draw a progress 
bar etc. in the main GUI thread.

But this doesn't seem to be possible. I may not pass it to the slot, 
because it's connected to a void signal. I also can't bind it, because I 
would bind an object which is already outdated. I tried that, in the 
hopes that it's always the same object, just with updated date (which 
would make sense), but making calls on the info object when I bind it 
segfaults, so I guess it's a dangling reference.

What can I do? There must be a way to pass information through the 
tunnel? The examples delivered with glibmm don't do that so they didn't 
help.

Thanks,
Matthias