[Gtk-sharp-list] Threading problem on Windows

[Michael Hutchinson]

On Mon, Dec 1, 2008 at 4:54 PM, D. Dobrev <dpldobrev at yahoo.com> wrote:
>
> Hello.
> I have the following code:
> protected virtual void OnButtonOneDieClicked(object sender, EventArgs e)
>        {
>                if (this.isDieRolling)
>                {
>                        this.isDieRolling = false;
>                }
>                else
>                {
>                        this.isDieRolling = true;
>                        Thread thread = new Thread(() =>
>                                                   {
>                                                                while (this.isDieRolling)
>                                                                {
>                                                                        Thread.Sleep(1);
>                                                                        Application.Invoke((image, args) =>
>                                                                                                           {
>
> this.imageOneDie.Pixbuf = this.RollDie();
>                                                                                                           });
>                                                                }
>                                                   });
>                        thread.Start();
>                }
>        }
>
> Its purpose is: when the button is first clicked, a few pictures (the sides
> of a die) begin rapidly changing. The second click stops the changes (this
> simulates the rolling of a die). In Linux this works perfectly, but in
> Windows the rolling rate is variable: it begins fast, then it slows down,
> then again fast, etc., with random intervals. Does anyone have an idea what
> the problem might be? If this helps, the source of my application can be
> found attached at the bottom of my
> http://www.nabble.com/forum/ViewPost.jtp?post=20758097&framed=y previous
> thread .

You don't need a thread here -- all it's giving you is semi-random
intervals of calling this.imageOneDie.Pixbuf = this.RollDie().
Thread.Sleep causes a context switch, so the thread's rate depends on
the OS' scheduler. The Application.Invoke is run on another thread
(the GTK# thread), so this also depends on the scheduler.

I recommend a GLib.Timeout: see
http://www.mono-project.com/Responsive_Applications#Timeouts and
http://www.go-mono.com/docs/monodoc.ashx?link=T%3aGLib.Timeout

It runs directly on the GTK thread at a specified rate, e.g. 30FPS
(33ms / frame):

protected virtual void OnButtonOneDieClicked(object sender, EventArgs e)
{
    if (this.isDieRolling) {
        this.isDieRolling = false;
    } else {
        this.isDieRolling = true;
        GLib.Timeout.Add (33, delegate {
            this.imageOneDie.Pixbuf = this.RollDie();
            return this.isDieRolling;
        });
    }
}

There may be other factors involved, but the thread certainly isn't
doing any good.

-- 
Michael Hutchinson
http://mjhutchinson.com