GDK Threads not allowing gtk changes(Making timer)

Question

 #include <gtk/gtk.h>
 #include<string.h>
 #include<stdio.h>
 #include <stdbool.h>
 #include<stdlib.h>

 static GtkWidget *textlabel_question_no;
 static GtkWidget *textlabel_answer1;
 static GtkWidget *textlabel_answer2;
 static GtkWidget *textlabel_answer3;
 static GtkWidget *textlabel_answer4;
 static GtkWidget *textlabel_question;
 static GtkWidget *textlabel_timer;
 static GtkWidget *textlabel_timeleft;
 static GtkWidget *button_next;
 static GtkWidget *window2;
 static GtkWidget *window31;
 static GThread  *thread;

 void show_info(GtkWidget *window2);

 // thread for timer
 static gpointer thread_Func(gpointer data)
 {

  // gdk_threads_enter();
int min=0,sec;//min=29

while(min > -1 )
{
    sec = 10;
    while(sec>=0)
    {
       sleep(1);
      char* timer_text=malloc(sizeof(char)*40);
      if(sec>9)
      {
        sprintf(timer_text,"%d : %d",min,sec);
      }
      else
      {
        sprintf(timer_text,"%d : 0%d",min,sec);
      }
      gtk_label_set_text(GTK_LABEL(textlabel_timer),timer_text);
      sec--;
    }
    min--;
    }
   // gdk_threads_leave();

    // gdk_threads_enter();
      g_printf("in show_info\n");
      GtkWidget *dialog;
      dialog = gtk_message_dialog_new(GTK_WINDOW(window2),
                     GTK_DIALOG_DESTROY_WITH_PARENT,
                     GTK_MESSAGE_INFO,
                     GTK_BUTTONS_OK,
             "Your Time is UP !!!\n Lets see the Result & Statistics...","title");                         
         gtk_window_set_title(GTK_WINDOW(dialog), "Time Finished");
         gint result=gtk_dialog_run(GTK_DIALOG(dialog));

         switch(result)
            {
              case GTK_RESPONSE_OK:
              gtk_widget_hide(window2);
             g_printf("in show_info\n");

            system("./result &");
            //gtk_main_quit();
            break;
           }
          //sleep(10);
       gtk_widget_destroy(dialog);


     /*
     window31 = gtk_window_new (GTK_WINDOW_TOPLEVEL);
     gtk_window_set_position(GTK_WINDOW(window31), GTK_WIN_POS_CENTER);
     gtk_window_set_title(GTK_WINDOW(window31), "Examination Panel");
     gtk_container_set_border_width(GTK_CONTAINER(window31),12);
     gtk_window_set_resizable(GTK_WINDOW(window31),FALSE);
     gtk_widget_set_size_request(window31,300,150);
     gtk_widget_show_all(window31);
     //sleep(10);
      gdk_threads_leave();*/
     return NULL;
   }

    static void next_question_label_change(GtkWidget *button_next,gpointer data)
     { 
     g_printf("in button_next\n");
     static int question_value=2;
     char *question_label = malloc(sizeof(char)*50);
     sprintf(question_label,"Question %d of 10.",question_value);
     gtk_label_set_text(GTK_LABEL(textlabel_question_no),question_label);
     if(question_value<10)
       question_value++;
   }



     //For Submit button dialog box
     static void test_submit_window(GtkWidget *button_next,GtkWidget *window2)
     {
       GtkWidget *dialog;
       dialog = gtk_message_dialog_new(GTK_WINDOW(window2),
                 GTK_DIALOG_DESTROY_WITH_PARENT,
                 GTK_MESSAGE_QUESTION,
                 GTK_BUTTONS_YES_NO,
                 "Are you sure to Submit the Test?");

     gtk_window_set_title(GTK_WINDOW(dialog), "Submit Test Confirmation");
     gint result = gtk_dialog_run (GTK_DIALOG (dialog));


     switch(result)
      {
      case GTK_RESPONSE_YES:

      system("./result &");
      gtk_widget_hide(window2);
            break;
      case GTK_RESPONSE_NO:
      break;
      }
     gtk_widget_destroy(dialog);

   }

     int
    main (int argc,char *argv[])
    {   

     GTimer *g_time;

     GtkWidget *fixed;
     GtkWidget *radio1,*radio2,*radio3,*radio4;
     GtkWidget *button_submit;
     GtkWidget *textlabel_title;
     GtkWidget *image;
     GtkWidget *image2;
     GError *error = NULL;
     GdkPixbuf *pixbuf;  
     GtkWidget *scrolled_window;


     /* Secure glib */
      if( ! g_thread_supported() )
    g_thread_init( NULL );

     //g_threads_init(NULL);
      //g_thread_init(NULL);
      /* Secure gtk */
      gdk_threads_init();

      /* Obtain gtk's global lock */



    // intialiazation
     gtk_init (&argc, &argv);




     //window attributes position,size,title
     window2 = gtk_window_new (GTK_WINDOW_TOPLEVEL);
     gtk_window_set_position(GTK_WINDOW(window2), GTK_WIN_POS_CENTER);
     gtk_window_set_title(GTK_WINDOW(window2), "Examination Panel");
     gtk_container_set_border_width(GTK_CONTAINER(window2),12);
     gtk_window_set_resizable(GTK_WINDOW(window2),FALSE);
     gtk_widget_set_size_request(window2,800,450);

     button_next = gtk_button_new_with_label("Next>>");
     button_submit = gtk_button_new_with_label("Submit");

     textlabel_title = gtk_label_new("-> TECHNICAL EXAM <-");
     textlabel_question = gtk_label_new("question placed here");
     textlabel_question_no = gtk_label_new(" Question 1 of 10.");
     textlabel_answer1 = gtk_label_new(" answer 1");
     textlabel_answer2 = gtk_label_new(" answer 2");
     textlabel_answer3 = gtk_label_new(" answer 3");
     textlabel_answer4 = gtk_label_new(" answer 4");
     textlabel_timer =   gtk_label_new("30:00");
     textlabel_timeleft = gtk_label_new("Time Left  :");



     //radio button for option
    radio1 =  gtk_radio_button_new_with_label (NULL , "A. ");
    radio2 =  gtk_radio_button_new_with_label_from_widget
            (GTK_RADIO_BUTTON(radio1),"B.");                         
     radio3 = gtk_radio_button_new_with_label_from_widget
             (GTK_RADIO_BUTTON (radio1),"C. ");
     radio4 = gtk_radio_button_new_with_label_from_widget
              (GTK_RADIO_BUTTON (radio1),"D. ");


  // For image
     pixbuf = gdk_pixbuf_new_from_file_at_size 
             ("/home/trilok/trantorlogo.png", 100,  100, &error);
   if(!pixbuf)
    {
   g_print ("Error: %s\n",error->message);
    g_error_free (error);
  /* Handle error here */
  }
  image = gtk_image_new_from_pixbuf(pixbuf);
  image2 = gtk_image_new_from_pixbuf(pixbuf);
  g_object_unref (pixbuf);




 //For Signals
 g_signal_connect (window2, "destroy", G_CALLBACK (gtk_main_quit), NULL);
 g_signal_connect (button_next,"clicked",G_CALLBACK
            (next_question_label_change), NULL);
 g_signal_connect (button_submit,"clicked",G_CALLBACK(test_submit_window),window2);


 //timer

 // pthread_create(&pth,NULL,threadFunc,"foo");
 /* Create new thread */
  thread = g_thread_create( thread_Func,NULL,
                          FALSE,&error);
  if( ! thread )
  {
    g_print( "Error: %s\n", error->message );
    return( -1 );
  }


  // For scrolled window 
  scrolled_window = gtk_scrolled_window_new (NULL, NULL);
  gtk_container_set_border_width (GTK_CONTAINER (scrolled_window),10);
   gtk_scrolled_window_set_policy 
         (GTK_SCROLLED_WINDOW     
           (scrolled_window)
        ,GTK_POLICY_AUTOMATIC, GTK_POLICY_ALWAYS);


   //fixed
   fixed = gtk_fixed_new();
   gtk_container_add(GTK_CONTAINER(window2), fixed);
  gtk_widget_show(fixed);
  gtk_scrolled_window_add_with_viewport
             (GTK_SCROLLED_WINDOW(scrolled_window),textlabel_question);
  gtk_widget_set_size_request(scrolled_window,580,150);


 //scrolled border
  gtk_scrolled_window_set_shadow_type (GTK_SCROLLED_WINDOW (scrolled_window),
                   GTK_SHADOW_IN);
  gtk_scrolled_window_set_placement (GTK_SCROLLED_WINDOW (scrolled_window),
                 GTK_CORNER_TOP_LEFT);




  gtk_fixed_put(GTK_FIXED(fixed), scrolled_window, 70, 110);
  gtk_fixed_put(GTK_FIXED(fixed), image, 0, 0);
  gtk_fixed_put(GTK_FIXED(fixed), image2, 0, 510);
  gtk_fixed_put(GTK_FIXED(fixed), textlabel_title, 300, 20);
  gtk_fixed_put(GTK_FIXED(fixed), textlabel_timeleft, 610, 70);  
  gtk_fixed_put(GTK_FIXED(fixed), textlabel_timer, 690, 70);  
  gtk_fixed_put(GTK_FIXED(fixed), textlabel_question_no, 65, 70);  
  gtk_fixed_put(GTK_FIXED(fixed), textlabel_answer1,170, 300);
  gtk_fixed_put(GTK_FIXED(fixed), textlabel_answer2,170, 350);
  gtk_fixed_put(GTK_FIXED(fixed), textlabel_answer3,170, 400);
  gtk_fixed_put(GTK_FIXED(fixed), textlabel_answer4,170, 450);
  gtk_fixed_put(GTK_FIXED(fixed), radio1, 100,300);
  gtk_fixed_put(GTK_FIXED(fixed), radio2, 100,350);
  gtk_fixed_put(GTK_FIXED(fixed), radio3, 100,400);
  gtk_fixed_put(GTK_FIXED(fixed), radio4, 100,450);
  gtk_fixed_put(GTK_FIXED(fixed), button_next,620, 500);
  gtk_fixed_put(GTK_FIXED(fixed), button_submit,690, 500);
  gtk_widget_show_all(window2);


   //gdk_threads_enter();
   GDK_THREADS_ENTER();
    gtk_main();

   /* Release gtk's global lock */
   //gdk_threads_leave();
    GDK_THREADS_LEAVE();

 return 0;
 }

Actually i am making an timer on exam simulator . My timer is working correctly but the problem is this i have to open an dialog box when timer goes to 0:00. her i am have implemented the threads to make an timer. Problem is this when timer goes to 0:00 then i segmentation fault. the gdk thread is not allowing any call to gtk widget.

Thanks for the help in advance. Some rectify the above code an make it happen will be appreciated

Answer 1

1. It's not clear if you're using gdk_threads_enter() or not, since there's a bunch of commented-out calls and a macro instead. GTK+ is not thread-safe, what you're trying is not the proper way.
2. You really shouldn't need a thread for this, just use a glib timer.
3. You're leaking the memory from the timer_text allocation; gtk_label_set_text() does not transfer ownership of the text buffer (notice that it's const).