Observer

/* -*-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_OBSERVER
#define OSG_OBSERVER 1

#include <OpenThreads/Mutex>
#include <osg/Referenced>
#include <set>

namespace osg {

/** Observer base class for tracking when objects are unreferenced (there reference count goes to 0) and are being deleted.*/
class OSG_EXPORT Observer
{
    public:
        Observer();
        virtual ~Observer();

        /** objectDeleted is called when the observed object is about to be deleted.  The observer will be automatically
        * removed from the observerd objects observer set so there is no need for the objectDeleted implementation
        * to call removeObserver() on the observed object. */
        virtual void objectDeleted(void*) {}

};

/** Class used by osg::Referenced to track the observers associated with it.*/
class OSG_EXPORT ObserverSet : public osg::Referenced
{
    public:

        ObserverSet(const Referenced* observedObject);

        Referenced* getObserverdObject() { return _observedObject; }
        const Referenced* getObserverdObject() const { return _observedObject; }

        /** "Lock" a Referenced object i.e., protect it from being deleted
          *  by incrementing its reference count.
          *
          * returns null if object doesn't exist anymore. */
        Referenced* addRefLock();

        inline OpenThreads::Mutex* getObserverSetMutex() const { return &_mutex; }

        void addObserver(Observer* observer);
        void removeObserver(Observer* observer);

        void signalObjectDeleted(void* ptr);

        typedef std::set<Observer*> Observers;
        Observers& getObservers() { return _observers; }
        const Observers& getObservers() const { return _observers; }

    protected:

        ObserverSet(const ObserverSet& rhs): osg::Referenced(rhs) {}
        ObserverSet& operator = (const ObserverSet& /*rhs*/) { return *this; }
        virtual ~ObserverSet();

        mutable OpenThreads::Mutex      _mutex;
        Referenced*                     _observedObject;
        Observers                       _observers;
};

}

#endif