gtk_label_set_text() segmentation fault - c

Question

Here is my code.
#include <gtk/gtk.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <stdlib.h>
#define MAX_LENGTH 8
#define WIDGET_NUM 3
typedef struct Widget
{
GtkWidget *window;
GtkWidget *button[WIDGET_NUM];
GtkWidget *entry[WIDGET_NUM];
GtkWidget *label[WIDGET_NUM];
GtkWidget *grid;
pthread_t pid[WIDGET_NUM];
int button_num;
}Widget;
void num_2_time(int num, char *buf)
{
int h = num / 3600;
int m = num % 3600 / 60;
int s = num % 60;
sprintf(buf, "%d:%d:%d", h, m, s);
}
void *wait_4_waking(void *arg)
{
Widget *window = (Widget*)arg;
int input_num, window_num = window->button_num;
const char *text;
char buf[MAX_LENGTH * 2];
text = gtk_entry_get_text(GTK_ENTRY(window->entry[window_num]));
input_num = atoi(text);
gtk_entry_set_text(GTK_ENTRY(window->entry[window_num]), "");
while (input_num >= 0)
{
num_2_time(input_num, buf);
//Segmentation fault
gtk_label_set_text(GTK_LABEL(window->label[window_num]), buf);
sleep(1);
input_num--;
}
return NULL;
}
void button_clicked_0(GtkWidget *widget, gpointer data)
{
Widget *window = (Widget*)data;
window->button_num = 0;
printf("%u\n", window->pid[0]);
if (window->pid[0] > 0)
{
pthread_cancel(window->pid[0]);
}
pthread_create(window->pid, NULL, wait_4_waking, data);
}
void button_clicked_1(GtkWidget *widget, gpointer data)
{
Widget *window = (Widget*)data;
window->button_num = 1;
if (window->pid[1] > 0)
{
pthread_cancel(window->pid[1]);
}
pthread_create(window->pid+1, NULL, wait_4_waking, data);
}
void button_clicked_2(GtkWidget *widget, gpointer data)
{
Widget *window = (Widget*)data;
window->button_num = 2;
if (window->pid[2] > 0)
{
pthread_cancel(window->pid[2]);
}
pthread_create(window->pid+2, NULL, wait_4_waking, data);
}
int main (int argc, char **argv)
{
Widget window;
int i;
void (*button_clicked[WIDGET_NUM])(GtkWidget*, gpointer) = {
button_clicked_0, button_clicked_1, button_clicked_2
};
gtk_init(&argc, &argv);
window.window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_title (GTK_WINDOW (window.window), "Window");
gtk_window_set_default_size (GTK_WINDOW (window.window), 400, 200);
window.grid = gtk_grid_new();
for (i = 0; i < WIDGET_NUM; i++)
{
window.entry[i] = gtk_entry_new();
window.label[i] = gtk_label_new("0:0:0");
window.button[i] = gtk_button_new_with_label("Go!");
window.pid[i] = 0;
gtk_entry_set_max_length(GTK_ENTRY(window.entry[i]), MAX_LENGTH);
gtk_grid_attach(GTK_GRID(window.grid), window.entry[i], 0, i, 1, 1);
gtk_grid_attach(GTK_GRID(window.grid), window.button[i], 1, i, 1, 1);
gtk_grid_attach(GTK_GRID(window.grid), window.label[i], 2, i, 1, 1);
}
gtk_container_add (GTK_CONTAINER (window.window), window.grid);
for (i = 0; i < WIDGET_NUM; i++)
{
g_signal_connect (window.button[i], "clicked", G_CALLBACK (button_clicked[i]), (gpointer)&window);
}
g_signal_connect (window.window, "destroy", G_CALLBACK(gtk_main_quit), NULL);
gtk_widget_show_all (window.window);
gtk_main();
return 0;
}
Building command:
gcc -o 1 test2.c `pkg-config --libs --cflags gtk+-3.0` -pthread -g
This error occurred when I clicked The button, but it didn't occur all the time. Before it occurred, I get an information below.
(1:18144): Pango-CRITICAL **: pango_layout_get_pixel_extents: assertion 'PANGO_IS_LAYOUT (layout)' failed
(1:18144): Pango-CRITICAL **: pango_layout_get_iter: assertion 'PANGO_IS_LAYOUT (layout)' failed
And then segmentation fault.
I checked its information by dmesg command. And I got this.
[ 703.437988] 1[6358]: segfault at 10 ip 00007f9b07ac3f91 sp 00007ffe3bd53790 error 4 in libpango-1.0.so.0.3800.1[7f9b07aa0000+48000]
How can I do for this error?

Answer 1

You are calling a Gtk+ widget function from another thread. Gtk+ is not thread safe so don't do that.
Your best option is to avoid threads: design your code so that the main loop is never blocked for long periods. Usually when I see threading problems, the use of threads is unnecessary and the whole mess could have been avoided by a cleaner design.
If the code can't be designed in a better way, then you'll need to use e.g. g_main_context_invoke() in your other thread to invoke a function in the main thread: that function can then modify the Gtk+ widget state safely. Be careful not to make mistakes with lifetimes of pointers that you share between threads.