ges: Avoid emitting 'child-added/removed' when signal emission stops addition

In the GESTimeline, TrackElement addition to a clip might get cancelled
(and thus the element gets removed), we need to make sure users do not
get wrong signals.

Also document the fact that user should connect to container::child-added
with g_signal_connect_after.

ges/ges-container.c

@@ -77,6 +77,10 @@ struct _GESContainerPrivate
    */
   GHashTable *mappings;
   guint nb_effects;
+
+  /* List of GESTimelineElement being in the "child-added" signal
+   * emission stage */
+  GList *adding_children;
 };
 
 enum
@@ -380,6 +384,9 @@ ges_container_class_init (GESContainerClass * klass)
    * @element: the #GESTimelineElement that was added.
    *
    * Will be emitted after a child was added to @container.
+   * Usually you should connect with #g_signal_connect_after
+   * as in the first emission stage, the signal emission might
+   * get stopped internally.
    */
   ges_container_signals[CHILD_ADDED_SIGNAL] =
       g_signal_new ("child-added", G_TYPE_FROM_CLASS (klass),
@@ -687,8 +694,10 @@ ges_container_add (GESContainer * container, GESTimelineElement * child)
 
   _ges_container_add_child_properties (container, child);
 
+  priv->adding_children = g_list_prepend (priv->adding_children, child);
   g_signal_emit (container, ges_container_signals[CHILD_ADDED_SIGNAL], 0,
       child);
+  priv->adding_children = g_list_remove (priv->adding_children, child);
 
   return TRUE;
 }
@@ -733,8 +742,13 @@ ges_container_remove (GESContainer * container, GESTimelineElement * child)
 
   _ges_container_remove_child_properties (container, child);
 
-  g_signal_emit (container, ges_container_signals[CHILD_REMOVED_SIGNAL], 0,
+  if (!g_list_find (container->priv->adding_children, child)) {
-      child);
+    g_signal_emit (container, ges_container_signals[CHILD_REMOVED_SIGNAL], 0,
+        child);
+  } else {
+    GST_INFO_OBJECT (container, "Not emitting 'child-removed' signal as child"
+        " removal happend during 'child-added' signal emission");
+  }
   gst_object_unref (child);
 
   return TRUE;

ges/ges-timeline.c

@@ -2276,13 +2276,14 @@ clip_track_element_added_cb (GESClip * clip,
 
   if (!tracks || tracks->len == 0) {
     GST_WARNING_OBJECT (timeline, "Got no Track to add %p (type %s), removing"
-        " from clip",
+        " from clip (stopping 'child-added' signal emission).",
         track_element, ges_track_type_name (ges_track_element_get_track_type
             (track_element)));
 
     if (tracks)
       g_ptr_array_unref (tracks);
 
+    g_signal_stop_emission_by_name (clip, "child-added");
     ges_container_remove (GES_CONTAINER (clip),
         GES_TIMELINE_ELEMENT (track_element));
 
@@ -2306,8 +2307,9 @@ clip_track_element_added_cb (GESClip * clip,
     }
   } else {
     GST_INFO_OBJECT (clip, "Already had a Source Element in %" GST_PTR_FORMAT
-        " of type %s, removing new one.", track,
+        " of type %s, removing new one. (stopping 'child-added' emission)",
-        G_OBJECT_TYPE_NAME (track_element));
+        track, G_OBJECT_TYPE_NAME (track_element));
+    g_signal_stop_emission_by_name (clip, "child-added");
     ges_container_remove (GES_CONTAINER (clip),
         GES_TIMELINE_ELEMENT (track_element));
   }
@@ -2331,8 +2333,9 @@ clip_track_element_added_cb (GESClip * clip,
       continue;
     } else {
       GST_INFO_OBJECT (clip, "Already had a Source Element in %" GST_PTR_FORMAT
-          " of type %s, removing new one.", track,
+          " of type %s, removing new one. (stopping 'child-added' emission)",
-          G_OBJECT_TYPE_NAME (track_element));
+          track, G_OBJECT_TYPE_NAME (track_element));
+      g_signal_stop_emission_by_name (clip, "child-added");
       ges_container_remove (GES_CONTAINER (clip),
           GES_TIMELINE_ELEMENT (track_element));
     }