Refactored the osg::Referenced observerset code so that it now uses a dedicated ObserverSet class,

which utilises a global recursive mutex that is dedicated to manage Observer and ObserverSet.

The new global mutex for observers avoids problems with deadlocks that were occurring previously when
an osg::Refenced object was being deleted at the same time as on osg::ObserverNodePath.

src/osg/Observer.cpp

@@ -0,0 +1,71 @@
+/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield
+ *
+ * This library is open source and may be redistributed and/or modified under
+ * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or
+ * (at your option) any later version.  The full license is in LICENSE file
+ * included with this distribution, and on the openscenegraph.org website.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * OpenSceneGraph Public License for more details.
+*/
+
+#include <osg/ObserverNodePath>
+#include <osg/Notify>
+
+using namespace osg;
+
+ObserverSet::ObserverSet()
+{
+    //OSG_NOTICE<<"ObserverSet::ObserverSet() "<<this<<std::endl;
+}
+
+ObserverSet::~ObserverSet()
+{
+    //OSG_NOTICE<<"ObserverSet::~ObserverSet() "<<this<<", _observers.size()="<<_observers.size()<<std::endl;
+}
+
+void ObserverSet::addObserver(Observer* observer)
+{
+    //OSG_NOTICE<<"ObserverSet::addObserver("<<observer<<") "<<this<<std::endl;
+    OpenThreads::ScopedLock<OpenThreads::Mutex> lock(*getObserverSetMutex());
+    _observers.insert(observer);
+}
+
+void ObserverSet::removeObserver(Observer* observer)
+{
+    //OSG_NOTICE<<"ObserverSet::removeObserver("<<observer<<") "<<this<<std::endl;
+    OpenThreads::ScopedLock<OpenThreads::Mutex> lock(*getObserverSetMutex());
+    _observers.erase(observer);
+}
+
+void ObserverSet::signalObjectUnreferenced(void* ptr)
+{
+    for(Observers::iterator itr = _observers.begin();
+        itr != _observers.end();
+        )
+    {
+        if ((*itr)->objectUnreferenced(ptr))
+        {
+            Observers::iterator orig_itr = itr;
+            ++itr;
+            _observers.erase(orig_itr);
+        }
+        else
+        {
+            ++itr;
+        }
+    }
+}
+
+void ObserverSet::signalObjectDeleted(void* ptr)
+{
+    for(Observers::iterator itr = _observers.begin();
+        itr != _observers.end();
+        ++itr)
+    {
+        (*itr)->objectDeleted(ptr);
+    }
+    _observers.clear();
+}