Introduced new osg::ObserverNodePath class that robustly manages a NodePath in a thread safe manner,

making it easier for users to track a NodePath even when nodes in the path get deleted.

include/osg/ObserverNodePath

@@ -0,0 +1,73 @@
+/* -*-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.
+*/
+
+#ifndef OSG_OBSERVERNODEPATH
+#define OSG_OBSERVERNODEPATH 1
+
+#include <osg/Node>
+#include <osg/Observer>
+#include <osg/ref_ptr>
+#include <list>
+
+namespace osg {
+
+typedef std::list< osg::ref_ptr<osg::Node> > RefNodePath;
+
+/** ObserverNodePath is an observer class for tracking changes to a NodePath,
+  * that automatically invalidates it when nodes are deleted.*/
+class OSG_EXPORT ObserverNodePath : public osg::Observer
+{
+    public:
+        ObserverNodePath();
+
+        ObserverNodePath(const ObserverNodePath& rhs);
+
+        ObserverNodePath(const osg::NodePath& nodePath);
+
+        ~ObserverNodePath();
+
+        ObserverNodePath& operator = (const ObserverNodePath& rhs);
+
+        bool valid() const { return _valid; }
+
+        void setNodePath(const osg::RefNodePath& nodePath);
+
+        void setNodePath(const osg::NodePath& nodePath);
+
+        void clearNodePath();
+
+        /** Get a thread safe RefNodePath.*/
+        bool getRefNodePath(RefNodePath& refNodePath) const;
+
+        /** Get a lightweight NodePath that isn't thread safe but
+          * may be safely used in single threaded applications, or when
+          * its known that the NodePath won't be invalidated during usage
+          * of the NodePath.*/
+        bool getNodePath(NodePath& nodePath) const;
+
+    protected:
+
+        void _setNodePath(const osg::NodePath& nodePath);
+
+        void _clearNodePath();
+
+        virtual bool objectUnreferenced(void* ptr);
+
+        mutable OpenThreads::Mutex      _mutex;
+        osg::NodePath                   _nodePath;
+        bool                            _valid;
+};
+
+}
+
+#endif