using threads and g_idle_add() in gtk+

/* compile with
 *      gcc -g -Wall try147.c `pkg-config gtk+-2.0 gthread-2.0 --cflags --libs`
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <gtk/gtk.h>

/* Restart dialog responses.
 */
typedef enum
{
  RESPONSE_RESTART,
  RESPONSE_CANCEL
} Resp;

/* Application state.
 */
typedef struct _App
{
  /* Background thread.
   */
  GThread *bg_thr;

  /* Label we update with progress.
   */
  GtkWidget *status;

  /* Main window.
   */
  GtkWidget *win;
} App;

/* A message from the worker.
 */
typedef struct _Msg
{
  App *app;
  char *text;
} Msg;

static gboolean
message_idle (Msg * msg)
{
  gtk_label_set_text (GTK_LABEL (msg->app->status), msg->text);

  g_free (msg->text);
  g_free (msg);

  return FALSE;
}

static void *background_thr (void *data);

static void
start_worker (App * app)
{
  if (!app->bg_thr)
    app->bg_thr = g_thread_new ("worker", background_thr, app);
}

static gboolean
alert_idle (App * app)
{
  GtkWidget *dia;
  GtkWidget *lab;
  Resp resp;

  dia = gtk_dialog_new_with_buttons ("Message", GTK_WINDOW (app->win),
                     GTK_DIALOG_DESTROY_WITH_PARENT |
                     GTK_DIALOG_MODAL,
                     "Restart", RESPONSE_RESTART,
                     "Cancel", RESPONSE_CANCEL, NULL);
  lab = gtk_label_new ("Error: restart worker?");
  gtk_container_add (GTK_CONTAINER (GTK_DIALOG (dia)->vbox), lab);
  gtk_widget_show_all (dia);
  resp = gtk_dialog_run (GTK_DIALOG (dia));
  gtk_widget_destroy (dia);

  if (resp == RESPONSE_RESTART)
    start_worker (app);

  return FALSE;
}

static gboolean
done_idle (App * app)
{
  app->bg_thr = NULL;

  gtk_label_set_text (GTK_LABEL (app->status), "idle");

  return FALSE;
}

static void *
background_thr (void *data)
{
  App *app = (App *) data;
  int i;
  Msg *msg;

  for (i = 0; i < 10; i++)
    {
      msg = g_new (Msg, 1);
      msg->app = app;
      msg->text = g_strdup_printf ("working %d ..", i);
      g_idle_add ((GSourceFunc) message_idle, msg);

      if ((rand () & 255) > 200)
    {
      g_idle_add ((GSourceFunc) alert_idle, app);
      break;
    }

      sleep (1);
    }

  g_idle_add ((GSourceFunc) done_idle, app);

  return (0);
}

static void
click_cb (GtkWidget * but, App * app)
{
  start_worker (app);
}

int
main (int argc, char **argv)
{
  App app;
  GtkWidget *vbox;
  GtkWidget *but;

  gtk_init (&argc, &argv);

  app.bg_thr = NULL;

  app.win = gtk_window_new (GTK_WINDOW_TOPLEVEL);

  /* Ought to kill the bg thread too I guess.
   */
  g_signal_connect (app.win, "destroy", G_CALLBACK (gtk_main_quit), NULL);

  vbox = gtk_vbox_new (FALSE, 2);
  gtk_container_add (GTK_CONTAINER (app.win), vbox);
  but = gtk_button_new_with_label ("Start bg thread");
  g_signal_connect (but, "clicked", G_CALLBACK (click_cb), &app);
  gtk_container_add (GTK_CONTAINER (vbox), but);
  app.status = gtk_label_new ("idle");
  gtk_container_add (GTK_CONTAINER (vbox), app.status);

  gtk_widget_show_all (app.win);

  gtk_main ();

  return 0;
}