Re: Multiple threads and drawing

[klaus triendl <klaus triendl eu>]

Germán Diago schrieb:
> Cool framework. I hadn't heard of it. Unfortunately, I'm not going to
> use it because it adds dependencies and I don't
> want more dependencies than boost and gtkmm.

sigx++ only needs tr1 and depends on glibmm when using the library. 
gtkmm depends on glibmm, too, so no extra dependencies. tr1 is already 
available with some compilers or it is available in newer boost releases.

> Anyway, the idea is not to make ANY gtk+ code from another thread
> which is not the GUI thread? In my threads code
> I use Gtk::Pixbuf::scale_simple to make thumbnails. Does that mean I
> cannot use it? Because if I can't I cannot make
> multithreaded code for what I want to.
> Or maybe I can as long as I don't draw anything in screen, and when the image is
> calculated I send it through a dispatcher and the GUI thread renders
> it? Is that the way to do it? Thanks in advance.

You are NOT probibited to call gtk+ code from threads other than the GUI 
thread. The point is to make _access_ to objects (e.g. your Gtk::Pixbuf) 
threadsafe (use a mutex, e.g.) and avoid calling functions of GUI 
objects (like the Gtk::Table or Gtk::Label) from other threads - this 
will make things much easier.
So, sending the calculated images through a dispatcher to the GUI thread 
is the way to go.



One question remains though: is sharing a Glib::RefPtr<> between 
multiple threads threadsafe, given that only one thread at a time 
accesses the actual object? Or asked differently: is 
Glib::ObjectBase::reference() and Glib::ObjectBase::unreference() 
threadsafe?


To Germán: please reply to all if you reply to a message...

Klaus