eventloop and abstractui debugging, lots more commenting on abstractui/eventloop implementation; minor tweaks elsewhere

git-svn-id: svn://localhost/ardour2/branches/3.0@12076 d708f5d6-7413-0410-9779-e7cbd77b26cf

1 files changed, 24 insertions, 3 deletions

diff --git a/libs/pbd/event_loop.cc b/libs/pbd/event_loop.cc
index 5a9a220075..5c132037d3 100644
--- a/libs/pbd/event_loop.cc
+++ b/libs/pbd/event_loop.cc
@@ -20,14 +20,35 @@ EventLoop::set_event_loop_for_thread (EventLoop* loop)
 	thread_event_loop.set (loop, do_not_delete_the_loop_pointer); 
 }
 
-/** Called when a sigc::trackable that was connected to using the invalidator() macro
- *  is destroyed.
- */
 void* 
 EventLoop::invalidate_request (void* data)
 {
         InvalidationRecord* ir = (InvalidationRecord*) data;
 
+	/* 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.
+	 */
+	
         if (ir->event_loop) {
 		Glib::Mutex::Lock lm (ir->event_loop->slot_invalidation_mutex());
 		for (list<BaseRequestObject*>::iterator i = ir->requests.begin(); i != ir->requests.end(); ++i) {