Load sessions asynchronously at startup

In an effort to minimize blocking calls in the "hot path"
(namely start up), this commit makes gdm invoke
the ConsoleKit GetSessions call asynchronously.

This change implies a slight semantic shift in the way the code
works.  Previously, it was guaranteed that all sessions were
loaded before the ck history file and passwd file were parsed.

Now, all the three tasks are asynchronous and race with each other.

This is "okay" to do because the code already allows sessions
to get added to existing users, and users to get created for
existing sessions.

There is still one GetSessions call that is synchronous.  This call is
during the middle of a user switch, so it's less critical.

https://bugzilla.gnome.org/show_bug.cgi?id=622639

1 files changed, 69 insertions, 22 deletions

diff --git a/gui/simple-greeter/gdm-user-manager.c b/gui/simple-greeter/gdm-user-manager.c
index f9eff90a..7138e961 100644
--- a/gui/simple-greeter/gdm-user-manager.c
+++ b/gui/simple-greeter/gdm-user-manager.c
@@ -56,6 +56,8 @@
 #define CK_SEAT_INTERFACE    "org.freedesktop.ConsoleKit.Seat"
 #define CK_SESSION_INTERFACE "org.freedesktop.ConsoleKit.Session"
 
+#define GDM_DBUS_TYPE_G_OBJECT_PATH_ARRAY (dbus_g_type_get_collection ("GPtrArray", DBUS_TYPE_G_OBJECT_PATH))
+
 /* Prefs Defaults */
 
 #ifdef __sun
@@ -82,6 +84,7 @@ struct GdmUserManagerPrivate
         GHashTable            *shells;
         DBusGConnection       *connection;
         DBusGProxy            *seat_proxy;
+        DBusGProxyCall        *get_sessions_call;
         char                  *seat_id;
 
         GFileMonitor          *passwd_monitor;
@@ -1165,6 +1168,10 @@ maybe_set_is_loaded (GdmUserManager *manager)
                 return;
         }
 
+        if (manager->priv->get_sessions_call != NULL) {
+                return;
+        }
+
         set_is_loaded (manager, TRUE);
 }
 
@@ -1632,26 +1639,40 @@ schedule_reload_passwd (GdmUserManager *manager)
 }
 
 static void
-load_sessions (GdmUserManager *manager)
+load_sessions_from_array (GdmUserManager     *manager,
+                          const char * const *session_ids,
+                          int                 number_of_sessions)
 {
-        gboolean    res;
-        GError     *error;
-        GPtrArray  *sessions;
-        int         i;
+        int i;
 
-        if (manager->priv->seat_proxy == NULL) {
-                g_debug ("GdmUserManager: no seat proxy; can't load sessions");
-                return;
+        for (i = 0; i < number_of_sessions; i++) {
+                maybe_add_session (manager, session_ids[i]);
         }
+}
+
+static void
+on_get_sessions_finished (DBusGProxy     *proxy,
+                          DBusGProxyCall *call,
+                          gpointer        data)
+{
+        GdmUserManager *manager;
+        GError         *error;
+        gboolean        res;
+        GPtrArray      *sessions;
+
+        manager = GDM_USER_MANAGER (data);
+
+        g_assert (manager->priv->get_sessions_call == call);
 
-        sessions = NULL;
         error = NULL;
-        res = dbus_g_proxy_call (manager->priv->seat_proxy,
-                                 "GetSessions",
-                                 &error,
-                                 G_TYPE_INVALID,
-                                 dbus_g_type_get_collection ("GPtrArray", DBUS_TYPE_G_OBJECT_PATH), &sessions,
-                                 G_TYPE_INVALID);
+        sessions = NULL;
+        res = dbus_g_proxy_end_call (proxy,
+                                     call,
+                                     &error,
+                                     GDM_DBUS_TYPE_G_OBJECT_PATH_ARRAY,
+                                     &sessions,
+                                     G_TYPE_INVALID);
+
         if (! res) {
                 if (error != NULL) {
                         g_warning ("unable to determine sessions for seat: %s",
@@ -1660,18 +1681,44 @@ load_sessions (GdmUserManager *manager)
                 } else {
                         g_warning ("unable to determine sessions for seat");
                 }
-                return;
         }
 
-        for (i = 0; i < sessions->len; i++) {
-                char *ssid;
+        manager->priv->get_sessions_call = NULL;
 
-                ssid = g_ptr_array_index (sessions, i);
+        g_assert (sessions->len <= G_MAXINT);
+        load_sessions_from_array (manager,
+                                  (const char * const *) sessions->pdata,
+                                  (int) sessions->len);
 
-                maybe_add_session (manager, ssid);
-        }
-        g_ptr_array_foreach (sessions, (GFunc)g_free, NULL);
+        g_ptr_array_foreach (sessions, (GFunc) g_free, NULL);
         g_ptr_array_free (sessions, TRUE);
+
+        maybe_set_is_loaded (manager);
+}
+
+static void
+load_sessions (GdmUserManager *manager)
+{
+        DBusGProxyCall *call;
+
+        if (manager->priv->seat_proxy == NULL) {
+                g_debug ("GdmUserManager: no seat proxy; can't load sessions");
+                return;
+        }
+
+        call = dbus_g_proxy_begin_call (manager->priv->seat_proxy,
+                                        "GetSessions",
+                                        on_get_sessions_finished,
+                                        manager,
+                                        NULL,
+                                        G_TYPE_INVALID);
+
+        if (call == NULL) {
+                g_warning ("GdmUserManager: failed to make GetSessions call");
+                return;
+        }
+
+        manager->priv->get_sessions_call = call;
 }
 
 static gboolean