bus: Only create the signalling socket pair when required

Otherwise a new one would be created for every single bus and
the process could easily run out of file descriptors.

Fixes bug #646624.

gst/gstbus.c

@@ -97,13 +97,34 @@ static guint gst_bus_signals[LAST_SIGNAL] = { 0 };
 struct _GstBusPrivate
 {
   guint num_sync_message_emitters;
-  GCond *queue_cond;
   GSource *watch_id;
 
   GstPoll *poll;
   GPollFD pollfd;
 };
 
+static void
+ensure_poll (GstBus * bus)
+{
+  if (g_atomic_pointer_get (&bus->priv->poll) == NULL) {
+    g_mutex_lock (bus->queue_lock);
+    if (!bus->priv->poll) {
+      GstPoll *poll;
+
+      poll = gst_poll_new_timer ();
+      gst_poll_get_read_gpollfd (poll, &bus->priv->pollfd);
+      g_atomic_pointer_set (&bus->priv->poll, poll);
+    }
+    g_mutex_unlock (bus->queue_lock);
+  }
+}
+
+static GstPoll *
+get_poll (GstBus * bus)
+{
+  return g_atomic_pointer_get (&bus->priv->poll);
+}
+
 G_DEFINE_TYPE (GstBus, gst_bus, GST_TYPE_OBJECT);
 
 /* fixme: do something about this */
@@ -189,10 +210,9 @@ gst_bus_init (GstBus * bus)
   bus->queue_lock = g_mutex_new ();
 
   bus->priv = G_TYPE_INSTANCE_GET_PRIVATE (bus, GST_TYPE_BUS, GstBusPrivate);
-  bus->priv->queue_cond = g_cond_new ();
 
-  bus->priv->poll = gst_poll_new_timer ();
+  /* Created on demand */
-  gst_poll_get_read_gpollfd (bus->priv->poll, &bus->priv->pollfd);
+  bus->priv->poll = NULL;
 
   GST_DEBUG_OBJECT (bus, "created");
 }
@@ -216,10 +236,10 @@ gst_bus_dispose (GObject * object)
     g_mutex_unlock (bus->queue_lock);
     g_mutex_free (bus->queue_lock);
     bus->queue_lock = NULL;
-    g_cond_free (bus->priv->queue_cond);
-    bus->priv->queue_cond = NULL;
 
+    if (bus->priv->poll)
       gst_poll_free (bus->priv->poll);
+    bus->priv->poll = NULL;
   }
 
   G_OBJECT_CLASS (parent_class)->dispose (object);
@@ -262,6 +282,7 @@ gst_bus_post (GstBus * bus, GstMessage * message)
   GstBusSyncHandler handler;
   gboolean emit_sync_message;
   gpointer handler_data;
+  GstPoll *poll;
 
   g_return_val_if_fail (GST_IS_BUS (bus), FALSE);
   g_return_val_if_fail (GST_IS_MESSAGE (message), FALSE);
@@ -281,6 +302,8 @@ gst_bus_post (GstBus * bus, GstMessage * message)
   emit_sync_message = bus->priv->num_sync_message_emitters > 0;
   GST_OBJECT_UNLOCK (bus);
 
+  poll = get_poll (bus);
+
   /* first call the sync handler if it is installed */
   if (handler)
     reply = handler (bus, message, handler_data);
@@ -301,7 +324,8 @@ gst_bus_post (GstBus * bus, GstMessage * message)
       /* pass the message to the async queue, refcount passed in the queue */
       GST_DEBUG_OBJECT (bus, "[msg %p] pushing on async queue", message);
       gst_atomic_queue_push (bus->queue, message);
-      gst_poll_write_control (bus->priv->poll);
+      if (poll)
+        gst_poll_write_control (poll);
       GST_DEBUG_OBJECT (bus, "[msg %p] pushed on async queue", message);
 
       break;
@@ -323,7 +347,8 @@ gst_bus_post (GstBus * bus, GstMessage * message)
       g_mutex_lock (lock);
 
       gst_atomic_queue_push (bus->queue, message);
-      gst_poll_write_control (bus->priv->poll);
+      if (poll)
+        gst_poll_write_control (poll);
 
       /* now block till the message is freed */
       g_cond_wait (cond, lock);
@@ -444,6 +469,8 @@ gst_bus_timed_pop_filtered (GstBus * bus, GstClockTime timeout,
   g_return_val_if_fail (GST_IS_BUS (bus), NULL);
   g_return_val_if_fail (types != 0, NULL);
 
+  ensure_poll (bus);
+
   g_mutex_lock (bus->queue_lock);
 
   while (TRUE) {
@@ -453,7 +480,7 @@ gst_bus_timed_pop_filtered (GstBus * bus, GstClockTime timeout,
         gst_atomic_queue_length (bus->queue));
 
     while ((message = gst_atomic_queue_pop (bus->queue))) {
-      gst_poll_read_control (bus->priv->poll);
+      gst_poll_read_control (get_poll (bus));
       GST_DEBUG_OBJECT (bus, "got message %p, %s, type mask is %u",
           message, GST_MESSAGE_TYPE_NAME (message), (guint) types);
       if ((GST_MESSAGE_TYPE (message) & types) != 0) {
@@ -488,7 +515,7 @@ gst_bus_timed_pop_filtered (GstBus * bus, GstClockTime timeout,
     }
 
     g_mutex_unlock (bus->queue_lock);
-    ret = gst_poll_wait (bus->priv->poll, timeout);
+    ret = gst_poll_wait (get_poll (bus), timeout);
     g_mutex_lock (bus->queue_lock);
 
     if (ret == 0) {
@@ -769,6 +796,7 @@ gst_bus_create_watch (GstBus * bus)
   source = (GstBusSource *) g_source_new (&gst_bus_source_funcs,
       sizeof (GstBusSource));
   source->bus = gst_object_ref (bus);
+  ensure_poll (bus);
   g_source_add_poll ((GSource *) source, &bus->priv->pollfd);
 
   return (GSource *) source;