+ /* Some of the requests queued with an EventLoop may involve functors
+ * that make method calls to objects whose lifetime is shorter
+ * than the EventLoop's. We do not want to make those calls if the
+ * object involve has been destroyed. To prevent this, we
+ * provide a way to invalidate those requests when the object is
+ * destroyed.
+ *
+ * An object was passed to __invalidator() which added a callback to
+ * EventLoop::invalidate_request() to its "notify when destroyed"
+ * list. __invalidator() returned an InvalidationRecord that has been
+ * to passed to this function as data.
+ *
+ * The object is currently being destroyed and so we want to
+ * mark all requests involving this object that are queued with
+ * any EventLoop as invalid.
+ *
+ * As of April 2012, we are usign sigc::trackable as the base object
+ * used to queue calls to ::invalidate_request() to be made upon
+ * destruction, via its ::add_destroy_notify_callback() API. This is
+ * not necessarily ideal, but it is very close to precisely what we
+ * want, and many of the objects we want to do this with already
+ * inherit (indirectly) from sigc::trackable.
+ */
+