From Pjotr Svetachov, "when you restart threading

with startThreading/stopThreading the _drawQueue and _availableQueue
are not reset properly. This can lead to a deadlock when threading is
started again. So before threading is started again the queues must be
reset. This deadlock is also reported earlier by someone else in here:
http://forum.openscenegraph.org/viewtopic.php?p=43415#43415"

include/osgViewer/Renderer

@@ -69,6 +69,8 @@ class OSGVIEWER_EXPORT Renderer : public osg::GraphicsOperation
 
         virtual void release();
 
+        virtual void reset();
+
         /** Force update of state associated with cameras. */
         void setCameraRequiresSetUp(bool flag);
         bool getCameraRequiresSetUp() const;
@@ -101,6 +103,9 @@ class OSGVIEWER_EXPORT Renderer : public osg::GraphicsOperation
             /** Release any thread waiting on the queue, even if the queue is empty. */
             void release();
 
+            /** Reset to fefault state (_isReleased = false)*/
+            void reset();
+
             /** Take a SceneView from the queue. Can return 0 if release() is called when the queue is empty. */
             osgUtil::SceneView* takeFront();