closing a GtkFileChooserDialog

[The Saltydog <thesaltydog gmail com>]

I have an annoying problem...

Open a GtkFileChooserDialog, select the file, click "Open"... then
execute a time-demanding subroutine. The dialog doesn't close until
the subroutine exists.

This is a snap of the code:
 ******************************************************
if (gtk_dialog_run (GTK_DIALOG (dialog)) == GTK_RESPONSE_ACCEPT)
        {
        char *filename;

        filename = gtk_file_chooser_get_filename (GTK_FILE_CHOOSER (dialog));
        my_subroutine(filename)
        g_free (filename);
                gtk_widget_destroy (dialog);
        }
        
        gtk_widget_destroy (dialog);
***********************************************************

the dialog stays open until my_subroutine returns and as the sub is a
very long time-demanding sub, it is annoying to see the dialog stuck
opened..