[gnome-session] gnome-session-check-accelerated: Avoid double checking

[Matthias Clasen <matthiasc src gnome org>]

commit ce2968402f20087cec2c5d9f4fc5eb7bbfb25903
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Mar 14 09:22:00 2011 -0400

    gnome-session-check-accelerated: Avoid double checking
    
    Add a mechanism to have a second gnome-session-check-accelerated
    instance wait until a first instance is done with the GL checks.
    This is meant to accomodate the situation where we run the check
    in the gdm login session, but the user quickly logs in, and
    gnome-session runs the check again.

 tools/gnome-session-check-accelerated.c |   84 +++++++++++++++++++++++++++++--
 1 files changed, 80 insertions(+), 4 deletions(-)
---
diff --git a/tools/gnome-session-check-accelerated.c b/tools/gnome-session-check-accelerated.c
index bd113df..2bd7993 100644
--- a/tools/gnome-session-check-accelerated.c
+++ b/tools/gnome-session-check-accelerated.c
@@ -29,6 +29,17 @@
 #include <gdk/gdkx.h>
 #include <X11/Xatom.h>
 
+/* Wait up to this long for a running check to finish */
+#define PROPERTY_CHANGE_TIMEOUT 5000
+
+/* Values used for the _GNOME_SESSION_ACCELERATED root window property */
+#define NO_ACCEL            0
+#define HAVE_ACCEL          1
+#define ACCEL_CHECK_RUNNING 2
+
+static Atom is_accelerated_atom;
+static gboolean property_changed;
+
 static void
 exit_1_message (const char *msg) G_GNUC_NORETURN;
 
@@ -39,12 +50,57 @@ exit_1_message (const char *msg)
   exit (1);
 }
 
+static gboolean
+on_property_notify_timeout (gpointer data)
+{
+        gtk_main_quit ();
+        return FALSE;
+}
+
+static GdkFilterReturn
+property_notify_filter (GdkXEvent *xevent,
+                        GdkEvent  *event,
+                        gpointer   data)
+{
+        XPropertyEvent *ev = xevent;
+
+        if (ev->type == PropertyNotify && ev->atom == is_accelerated_atom) {
+                property_changed = TRUE;
+                gtk_main_quit ();
+        }
+
+        return GDK_FILTER_CONTINUE;
+}
+
+static gboolean
+wait_for_property_notify (void)
+{
+        GdkDisplay *display = NULL;
+        GdkScreen *screen;
+        GdkWindow *root;
+        Window rootwin;
+
+        property_changed = FALSE;
+
+        display = gdk_display_get_default ();
+        screen = gdk_display_get_default_screen (display);
+        root = gdk_screen_get_root_window (screen);
+        rootwin = gdk_x11_window_get_xid (root);
+
+        XSelectInput (GDK_DISPLAY_XDISPLAY (display), rootwin, PropertyChangeMask);
+        gdk_window_add_filter (root, property_notify_filter, NULL);
+        g_timeout_add (PROPERTY_CHANGE_TIMEOUT, on_property_notify_timeout, NULL);
+
+        gtk_main ();
+
+        return property_changed;
+}
+
 int
 main (int argc, char **argv)
 {
         GdkDisplay *display = NULL;
         int estatus;
-        Atom is_accelerated_atom;
         char *child_argv[] = { LIBEXECDIR "/gnome-session-check-accelerated-helper", NULL };
         Window rootwin;
         glong is_accelerated;
@@ -64,6 +120,7 @@ main (int argc, char **argv)
                 gulong bytes_after;
                 guchar *data;
 
+ read:
                 gdk_x11_display_error_trap_push (display);
                 XGetWindowProperty (GDK_DISPLAY_XDISPLAY (display), rootwin,
                                     is_accelerated_atom,
@@ -73,12 +130,31 @@ main (int argc, char **argv)
 
                 if (type == XA_CARDINAL) {
                         glong *is_accelerated_ptr = (glong*) data;
-                        /* Exit 1 if the property is 0 (false) */
-                        return (*is_accelerated_ptr == 0) ? 1 : 0;
+
+                        if (*is_accelerated_ptr == ACCEL_CHECK_RUNNING) {
+                                /* Test in progress, wait */
+                                if (wait_for_property_notify ())
+                                        goto read;
+                                /* else fall through and do the check ourselves */
+
+                        } else {
+                                return (*is_accelerated_ptr == 0 ? 1 : 0);
+                        }
                 }
         }
 
-        /* We don't have the property or it's the wrong type.  Try to compute it now. */
+        /* We don't have the property or it's the wrong type.
+         * Try to compute it now.
+         */
+
+        /* First indicate that a test is in progress */
+        is_accelerated = ACCEL_CHECK_RUNNING;
+        XChangeProperty (GDK_DISPLAY_XDISPLAY (display),
+                         rootwin,
+                         is_accelerated_atom,
+                         XA_CARDINAL, 32, PropModeReplace, (guchar *) &is_accelerated, 1);
+
+        gdk_display_sync (display);
 
         estatus = 1;
         if (!g_spawn_sync (NULL, (char**)child_argv, NULL, 0,