/*
   xvfb-run --auto-servernum --server-args="-screen 0 640x480x24 -screen 1 640x480x24" -e /dev/stdout ./foo

*/

#include <stdio.h>
#include <stdlib.h>
#include <X11/Xlib.h>
#include <X11/extensions/sync.h>

int
main (void)
{
  int screen_number = 1;

  Display *display;
  Screen *screen;
  Window root;
  XSyncFence fence;
  int sync_major, sync_minor;

  display = XOpenDisplay (NULL);
  if (! display) { abort (); }

  if (screen_number >= ScreenCount(display)) {
    printf ("no screen number %d\n", screen_number);
    abort();
  }
  screen = ScreenOfDisplay(display, screen_number);

  root = RootWindowOfScreen(screen);
  printf ("root window %X\n", root);

  if (! XSyncInitialize(display, &sync_major, &sync_minor)) {
    printf ("cannot SyncInitialize\n");
    abort();
  }
  printf ("SYNC extension %d.%d\n", sync_major, sync_minor);

  fence = XSyncCreateFence(display, root, 0);
  XSync(display, 0);

  printf ("fence created successfully\n");
  return 0;
}