Re: hello & threads

[Tim Müller <zen18864 zen co uk>]

On Saturday 15 January 2005 12:27, david:: wrote:

> well i have a problem with an application i'm writing. I have 2
> threads. The first one creates an empty window with a button and calls
> gtk_main(). The second one does this:
>
> void  secondThread(){
>
>   char str[100];
>   int i=0;
>
>   while(TRUE) {
>
>     // here i create a string
>     sprintf(str, "%d\n", i++);
>
>     // and here I change the button label
>     if (window != NULL)
>       gtk_button_set_label(GTK_BUTTON(button), str);
>
>     // once a second
>     g_usleep(1000000);
>   }
> }
>
> well the thread is quite simple. But when i launch the program the
> button changes its label 3 or 4 times and then becomes blank.
>
> I well, i have been using gtk for a time and i have never had this
> problem. can you tell me what i am doing wrong??

Don't use Gtk or Gdk functions from any thread that's not the main GUI thread. 
If you do, you'll have to use locks (see http://www.gtk.org/faq/ for 
details), but I really don't recommend this.

In your case, you could do somthing like:

static gboolean
change_label (gchar *str)
{
 if (window != NULL)
  gtk_button_set_label (GTK_BUTTON (button), str);
 g_free (str);
 return FALSE; /* only once */
}

 .....

 // change label here
 g_idle_add ((GSourceFunc) change_label, g_strdup (str));

 ....

change_label will be called as soon as possible from the context of the main 
thread.

I assume this is just a simple example. Because if not, you don't need threads 
at all, just do something like:

static gboolean
update_button (gpointer the_button)
{
 static gint i; /* 0 */
 gchar *str;

 str = g_strdup_printf ("%d", i++);
 gtk_button_set_label (GTK_BUTTON (the_button), str);
 g_free (str);
 
 return TRUE; /* call again */
}


and then .....

      .... set up window etc....

      button = gtk_button_new ( .... );

      g_timeout_add (1 * 1000, update_button, button);

     gtk_main ();


That way the function update_button() will be called once per second (until 
you return FALSE).

Cheers
 -Tim