gtk_entry_set_text used twice or more

[author <millward Ms UManitoba CA>]

I'm just learning GTK from the online tutor and writing my
own experiment programs. 
I have a small problem with  the Text Entry Widget.
I want to display a message on it, then sleep 10 seconds,
then display another different message on it.
The first message is a character string.
The second is the result of a calcuation converted to
a character string.
void callback2(GtkWidget * widget, GtkWidget * entry )
{
  double dub = 0.0;
  char savebuf[50];
  gchar * xx;
  gchar * yy = "This is callback2... ";

  xx = gtk_entry_get_text(GTK_ENTRY(entry) );

  g_print("\nEntry Contents >  %s\n",  xx);

  dub = process(xx);

/* The next line is not executed. Why? */
  gtk_entry_set_text(GTK_ENTRY(entry), yy);

  sleep(10);  /* in <unistd.h> */

  sprintf(savebuf,"%g",dub);  /* in <stdio.h> */
  gtk_entry_set_text(GTK_ENTRY(entry), (gchar *) savebuf );

}
  The g_print message gets onto the xterm command line,
then the program waits 10 seconds and displays the
result of the calculation in the Entry Widget, but
the  line :
gtk_entry_set_text(GTK_ENTRY(entry), yy);
is skipped and does nothing. 
Why? Can anyone tell me why the string is not displayed?
This program compiles clean with no warnings.