OpenSceneGraph/include/osgDB/DatabasePager

/* -*-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 OSGDB_DATABASEPAGER
#define OSGDB_DATABASEPAGER 1

#include <osg/NodeVisitor>
#include <osg/Group>
#include <osg/PagedLOD>
#include <osg/Drawable>
#include <osg/GraphicsThread>
#include <osg/FrameStamp>
#include <osg/ObserverNodePath>
#include <osg/observer_ptr>

#include <OpenThreads/Thread>
#include <OpenThreads/Mutex>
#include <OpenThreads/ScopedLock>
#include <OpenThreads/Condition>

#include <osgUtil/IncrementalCompileOperation>

#include <osgDB/SharedStateManager>
#include <osgDB/ReaderWriter>
#include <osgDB/Options>


#include <map>
#include <list>
#include <algorithm>
#include <functional>

namespace osgDB {



/** Database paging class which manages the loading of files in a background thread, 
  * and synchronizing of loaded models with the main scene graph.*/
class OSGDB_EXPORT DatabasePager : public osg::NodeVisitor::DatabaseRequestHandler
{
    public :

        typedef OpenThreads::Thread::ThreadPriority ThreadPriority;

        DatabasePager();

        DatabasePager(const DatabasePager& rhs);

        virtual const char* className() const { return "DatabasePager"; }

        /** Create a shallow copy on the DatabasePager.*/
        virtual DatabasePager* clone() const { return new DatabasePager(*this); }

        /** get the prototype singleton used by DatabasePager::create().*/
        static osg::ref_ptr<DatabasePager>& prototype();
        
        /** create a DatabasePager by cloning DatabasePager::prototype().*/
        static DatabasePager* create();

        

        /** Add a request to load a node file to end the the database request list.*/
        virtual void requestNodeFile(const std::string& fileName,osg::Group* group,
                                     float priority, const osg::FrameStamp* framestamp,
                                     osg::ref_ptr<osg::Referenced>& databaseRequest,
                                     const osg::Referenced* options);

        /** Set the priority of the database pager thread(s).*/
        int setSchedulePriority(OpenThreads::Thread::ThreadPriority priority);

        /** Cancel the database pager thread(s).*/        
        virtual int cancel();
        
        virtual bool isRunning() const;
        
        /** Clear all internally cached structures.*/
        virtual void clear();
        
        class OSGDB_EXPORT DatabaseThread : public osg::Referenced, public OpenThreads::Thread
        {
        public:
        
            enum Mode
            {
                HANDLE_ALL_REQUESTS,
                HANDLE_NON_HTTP,
                HANDLE_ONLY_HTTP
            };
        
            DatabaseThread(DatabasePager* pager, Mode mode, const std::string& name);
            
            DatabaseThread(const DatabaseThread& dt, DatabasePager* pager);

            void setName(const std::string& name) { _name = name; }
            const std::string& getName() const { return _name; }

            void setDone(bool done) { _done = done; }
            bool getDone() const { return _done; }
            
            void setActive(bool active) { _active = active; }
            bool getActive() const { return _active; }

            double getTimeSinceStartOfIteration() const;

            virtual int cancel();
            
            virtual void run();
            
        protected:

            virtual ~DatabaseThread();
        
            bool            _done;
            bool            _active;
            DatabasePager*  _pager;
            Mode            _mode;
            std::string     _name;
            osg::Timer_t    _tickSinceStartOfIteration;

        };
        
        void setUpThreads(unsigned int totalNumThreads=2, unsigned int numHttpThreads=1);

        unsigned int addDatabaseThread(DatabaseThread::Mode mode, const std::string& name);

        DatabaseThread* getDatabaseThread(unsigned int i) { return _databaseThreads[i].get(); }
        
        const DatabaseThread* getDatabaseThread(unsigned int i) const { return _databaseThreads[i].get(); }

        unsigned int getNumDatabaseThreads() const { return _databaseThreads.size(); }
        
        /** Set whether the database pager thread should be paused or not.*/
        void setDatabasePagerThreadPause(bool pause);
        
        /** Get whether the database pager thread should is paused or not.*/
        bool getDatabasePagerThreadPause() const { return _databasePagerThreadPaused; }
        
        /** Set whether new database request calls are accepted or ignored.*/
        void setAcceptNewDatabaseRequests(bool acceptNewRequests) { _acceptNewRequests = acceptNewRequests; }
        
        /** Get whether new database request calls are accepted or ignored.*/
        bool getAcceptNewDatabaseRequests() const { return _acceptNewRequests; }
        
        /** Get the number of frames that are currently active.*/
        int getNumFramesActive() const { return _numFramesActive; }

        /** Signal the database thread that the update, cull and draw has begun for a new frame.
          * Note, this is called by the application so that the database pager can go to sleep while the CPU is busy on the main rendering threads. */
        virtual void signalBeginFrame(const osg::FrameStamp* framestamp);
        
        /** Signal the database thread that the update, cull and draw dispatch has completed.
          * Note, this is called by the application so that the database pager can go to wake back up now the main rendering threads are iddle waiting for the next frame.*/
        virtual void signalEndFrame();
        

        /** Find all PagedLOD nodes in a subgraph and register them with 
          * the DatabasePager so it can keep track of expired nodes.
          * note, should be only be called from the update thread. */
        virtual void registerPagedLODs(osg::Node* subgraph, int frameNumber = 0);

        /** Set the incremental compile operation.
          * Used to manage the OpenGL object compilation and merging of subgraphs in a way that avoids overloading
          * the rendering of frame with too many new objects in one frame. */
        void setIncrementalCompileOperation(osgUtil::IncrementalCompileOperation* ico);

        /** Get the incremental compile operation. */
        osgUtil::IncrementalCompileOperation* getIncrementalCompileOperation() { return _incrementalCompileOperation.get(); }


        /** Set whether the database pager should pre compile OpenGL objects before allowing
          * them to be merged into the scene graph.
          * Pre compilation helps reduce the chances of frame drops, but also slows the
          * speed at which tiles are merged as they have to be compiled first.*/
        void setDoPreCompile(bool flag) { _doPreCompile = flag; }

        /** Get whether the database pager should pre compile OpenGL objects before allowing
          * them to be merged into the scene graph.*/
        bool getDoPreCompile() const { return _doPreCompile; }


        /** Set the target frame rate that the DatabasePager should assume.
          * Typically one would set this to the value refresh rate of your display system i.e. 60Hz.
          * Default value is 100.
          * Usage notes.  The TargetFrameRate and the MinimumTimeAvailableForGLCompileAndDeletePerFrame
          * parameters are not directly used by DatabasePager, but are should be used as a guide for how
          * long to set aside per frame for compiling and deleting OpenGL objects - ie. the value to use 
          * when calling DatabasePager::compileGLObjectgs(state,availableTime,). The longer amount of
          * time to set aside  cthe faster databases will be paged in but with increased chance of frame drops,
          * the lower the amount of time the set aside the slower databases will paged it but with better
          * chance of avoid any frame drops.  The default values are chosen to achieve the later when running
          * on a modern mid to high end  PC. 
          * The way to compute the amount of available time use a scheme such as :
          *    availableTime = maximum(1.0/targetFrameRate - timeTakenDuringUpdateCullAndDraw, minimumTimeAvailableForGLCompileAndDeletePerFrame). 
          */
        void setTargetFrameRate(double tfr) { _targetFrameRate = tfr; }

        /** Get the target frame rate that the DatabasePager should assume.*/
        double getTargetFrameRate() const { return _targetFrameRate; }
        
        /** Set the minimum amount of time (in seconds) that should be made available for compiling and delete OpenGL objects per frame.
          * Default value is 0.001 (1 millisecond). 
          * For usage see notes in setTargetFrameRate.*/
        void setMinimumTimeAvailableForGLCompileAndDeletePerFrame(double ta) { _minimumTimeAvailableForGLCompileAndDeletePerFrame = ta; }

        /** Get the minimum amount of time that should be made available for compiling and delete OpenGL objects per frame.
          * For usage see notes in setTargetFrameRate.*/
        double getMinimumTimeAvailableForGLCompileAndDeletePerFrame() const { return _minimumTimeAvailableForGLCompileAndDeletePerFrame; }

        /** Set the maximum number of OpenGL objects that the page should attempt to compile per frame.
          * Note, Lower values reduces chances of a frame drop but lower the rate that database will be paged in at.
          * Default value is 8. */
        void setMaximumNumOfObjectsToCompilePerFrame(unsigned int num) { _maximumNumOfObjectsToCompilePerFrame = num; }

        /** Get the maximum number of OpenGL objects that the page should attempt to compile per frame.*/
        unsigned int getMaximumNumOfObjectsToCompilePerFrame() const { return _maximumNumOfObjectsToCompilePerFrame; }


        /** Set the target maximum number of PagedLOD to maintain in memory.
          * Note, if more than the target number are required for rendering of a frame then these active PagedLOD are excempt from being expiried.
          * But once the number of active drops back below the target the inactive PagedLOD will be trimmed back to the target number.*/
        void setTargetMaximumNumberOfPageLOD(unsigned int target) { _targetMaximumNumberOfPageLOD = target; }

        /** Get the target maximum number of PagedLOD to maintain in memory.*/
        unsigned int getTargetMaximumNumberOfPageLOD() const { return _targetMaximumNumberOfPageLOD; }


        /** Deprecated.*/
        void setExpiryDelay(double expiryDelay) { _expiryDelay = expiryDelay; }
        
        /** Deprecated.*/
        double getExpiryDelay() const { return _expiryDelay; }

        /** Deprecated.*/
        void setExpiryFrames(int expiryFrames) { _expiryFrames = expiryFrames; }
        
        /** Deprecated.*/
        int getExpiryFrames() const { return _expiryFrames; }

        /** Deprecated.*/
        void setReleaseDelay(double releaseDelay);
        
        /** Deprecated.*/
        double getReleaseDelay() const { return _releaseDelay; }

        /** Deprecated.*/
        void setReleaseFrames(int releaseFrames) { _releaseFrames = releaseFrames; }
        
        /** Deprecated.*/
        int getReleaseFrames() const { return _releaseFrames; }


        /** Set whether the removed subgraphs should be deleted in the database thread or not.*/
        void setDeleteRemovedSubgraphsInDatabaseThread(bool flag) { _deleteRemovedSubgraphsInDatabaseThread = flag; }
        
        /** Get whether the removed subgraphs should be deleted in the database thread or not.*/
        bool getDeleteRemovedSubgraphsInDatabaseThread() const { return _deleteRemovedSubgraphsInDatabaseThread; }

        enum DrawablePolicy
        {
            DO_NOT_MODIFY_DRAWABLE_SETTINGS,
            USE_DISPLAY_LISTS,
            USE_VERTEX_BUFFER_OBJECTS,
            USE_VERTEX_ARRAYS
        };

        /** Set how loaded drawables should be handled w.r.t their display list/vertex buffer object/vertex array settings.*/
        void setDrawablePolicy(DrawablePolicy policy) { _drawablePolicy = policy; }

        /** Get how loaded drawables should be handled w.r.t their display list/vertex buffer object/vertex array settings.*/
        DrawablePolicy getDrawablePolicy() const { return _drawablePolicy; }


        /** Set whether newly loaded textures should have their UnrefImageDataAfterApply set to a specified value.*/
        void setUnrefImageDataAfterApplyPolicy(bool changeAutoUnRef, bool valueAutoUnRef) { _changeAutoUnRef = changeAutoUnRef; _valueAutoUnRef = valueAutoUnRef; }

        /** Get whether newly loaded textures should have their UnrefImageDataAfterApply set to a specified value.*/
        void getUnrefImageDataAfterApplyPolicy(bool& changeAutoUnRef, bool& valueAutoUnRef) const { changeAutoUnRef = _changeAutoUnRef; valueAutoUnRef = _valueAutoUnRef; }


        /** Set whether newly loaded textures should have their MaxAnisotopy set to a specified value.*/
        void setMaxAnisotropyPolicy(bool changeAnisotropy, float valueAnisotropy) { _changeAnisotropy = changeAnisotropy; _valueAnisotropy = valueAnisotropy; }

        /** Set whether newly loaded textures should have their MaxAnisotopy set to a specified value.*/
        void getMaxAnisotropyPolicy(bool& changeAnisotropy, float& valueAnisotropy) const { changeAnisotropy = _changeAnisotropy; valueAnisotropy = _valueAnisotropy; }


        /** Return true if there are pending updates to the scene graph that require a call to updateSceneGraph(double). */
        bool requiresUpdateSceneGraph() const;
        
        /** Merge the changes to the scene graph by calling calling removeExpiredSubgraphs then addLoadedDataToSceneGraph.
          * Note, must only be called from single thread update phase. */
        virtual void updateSceneGraph(const osg::FrameStamp& frameStamp);
                
        /** Turn the compilation of rendering objects for specified graphics context on (true) or off(false). */
        void setCompileGLObjectsForContextID(unsigned int contextID, bool on);
        
        /** Get whether the compilation of rendering objects for specified graphics context on (true) or off(false). */
        bool getCompileGLObjectsForContextID(unsigned int contextID);

        /** Return true if an external draw thread should call compileGLObjects(..) or not.*/
        bool requiresExternalCompileGLObjects(unsigned int contextID) const;

        /** Return true if there are pending compile operations that are required.
          * If requiresCompileGLObjects() return true the application should call compileGLObjects() .*/
        bool requiresCompileGLObjects() const;

        /** Compile the rendering objects (display lists,texture objects, VBO's) on loaded subgraph.
          * note, should only be called from the draw thread.
          * Note, must only be called from a valid graphics context. */
        virtual void compileGLObjects(osg::State& state,double& availableTime, bool doFlush = false);
        
        /** Compile the rendering objects (display lists,texture objects, VBO's) on loaded subgraph.
          * note, should only be called from the draw thread.
          * Note, must only be called from a valid graphics context. */
        virtual void compileAllGLObjects(osg::State& state, bool doFlush = false);

        /** Report how many items are in the _fileRequestList queue */
        unsigned int getFileRequestListSize() const { return _fileRequestQueue->size() + _httpRequestQueue->size(); }

        /** Report how many items are in the _dataToCompileList queue */
        unsigned int getDataToCompileListSize() const { return _dataToCompileList->size(); }
        
        /** Report how many items are in the _dataToMergeList queue */
        unsigned int getDataToMergeListSize() const { return _dataToMergeList->size(); }

        /** Report whether any requests are in the pager.*/
        bool getRequestsInProgress() const;
        
        /** Get the minimum time between the first request for a tile to be loaded and the time of its merge into the main scene graph.*/
        double getMinimumTimeToMergeTile() const { return _minimumTimeToMergeTile; }

        /** Get the maximum time between the first request for a tile to be loaded and the time of its merge into the main scene graph.*/
        double getMaximumTimeToMergeTile() const { return _maximumTimeToMergeTile; }

        /** Get the average time between the first request for a tile to be loaded and the time of its merge into the main scene graph.*/
        double getAverageTimeToMergeTiles() const { return (_numTilesMerges > 0) ? _totalTimeToMergeTiles/static_cast<double>(_numTilesMerges) : 0; }

        /** Reset the Stats variables.*/
        void resetStats();

        typedef std::set< osg::ref_ptr<osg::StateSet> >                 StateSetList;
        typedef std::vector< osg::ref_ptr<osg::Drawable> >              DrawableList;
        //typedef std::pair<StateSetList,DrawableList>                    DataToCompile;
        typedef osgUtil::IncrementalCompileOperation::CompileData       DataToCompile;
        typedef std::map< unsigned int, DataToCompile >                 DataToCompileMap; 
        typedef std::set<unsigned int>                                  ActiveGraphicsContexts;
        typedef std::vector< osg::observer_ptr<osg::GraphicsContext> >  CompileGraphicsContexts;

        class CountPagedLODsVisitor;

        struct PagedLODList : public osg::Referenced
        {
            virtual PagedLODList* clone() = 0;
            virtual void clear() = 0;
            virtual unsigned int size() = 0;
            virtual void moveInactivePagedLODTo(PagedLODList& inactivePagedLODList, const osg::FrameStamp& framestamp) = 0;
            virtual void moveActivePagedLODTo(PagedLODList& activePagedLODList, const osg::FrameStamp& framestamp) = 0;
            virtual void removeExpiredChildren(int& numberChildrenToRemove, double expiryTime, int expiryFrame, osg::NodeList& childrenRemoved) = 0;
            virtual void removeNodes(osg::NodeList& nodesToRemove) = 0;
            virtual void insertPagedLOD(const osg::observer_ptr<osg::PagedLOD>& plod) = 0;
            virtual bool containsPagedLOD(const osg::observer_ptr<osg::PagedLOD>& plod) const = 0;
        };


    protected:

        virtual ~DatabasePager();

        friend class DatabaseThread;
        friend struct DatabaseRequest;

        struct RequestQueue;

        struct DatabaseRequest : public osg::Referenced
        {
            DatabaseRequest():
                osg::Referenced(true),
                _valid(false),
                _frameNumberFirstRequest(0),
                _timestampFirstRequest(0.0),
                _priorityFirstRequest(0.f),
                _frameNumberLastRequest(0),
                _timestampLastRequest(0.0),
                _priorityLastRequest(0.0f),
                _numOfRequests(0),
                _requestQueue(0)
            {}

            void invalidate();

            bool valid() const { return _valid; }

            bool                                _valid;
            std::string                         _fileName;
            int                                 _frameNumberFirstRequest;
            double                              _timestampFirstRequest;
            float                               _priorityFirstRequest;
            int                                 _frameNumberLastRequest;
            double                              _timestampLastRequest;
            float                               _priorityLastRequest;
            unsigned int                        _numOfRequests;
            osg::ObserverNodePath               _observerNodePath;
            osg::Group*                         _groupForAddingLoadedSubgraph;
            osg::ref_ptr<osg::Node>             _loadedModel;
            DataToCompileMap                    _dataToCompileMap;
            osg::ref_ptr<Options>               _loadOptions;
            RequestQueue*                       _requestQueue;

            bool isRequestCurrent (int frameNumber) const
            {
                return _valid && (frameNumber - _frameNumberLastRequest <= 1);
            }
        };


        struct RequestQueue : public osg::Referenced
        {
        public:

            RequestQueue(DatabasePager* pager);

            void add(DatabaseRequest* databaseRequest);
            void addNoLock(DatabaseRequest* databaseRequest);

            void takeFirst(osg::ref_ptr<DatabaseRequest>& databaseRequest);

            /// prune all the old requests and then return true if requestList left empty
            bool pruneOldRequestsAndCheckIfEmpty();

            virtual void updateBlock() {}

            bool empty() const { return size()==0; }

            unsigned int size() const { return _size; }

            void clear();


            typedef std::list< osg::ref_ptr<DatabaseRequest> > RequestList;
            void swap(RequestList& requestList);

            DatabasePager*              _pager;
            unsigned int                _size;
            RequestList                 _requestList;
            OpenThreads::Mutex          _requestMutex;
            int                         _frameNumberLastPruned;

        protected:
            virtual ~RequestQueue();
        };

        
        typedef std::vector< osg::ref_ptr<DatabaseThread> > DatabaseThreadList;
        typedef std::vector<  osg::ref_ptr<osg::Object> > ObjectList;

        struct ReadQueue : public RequestQueue
        {
            ReadQueue(DatabasePager* pager, const std::string& name);

            void block() { _block->block(); }

            void release() { _block->release(); }

            virtual void updateBlock();


            osg::ref_ptr<osg::RefBlock> _block;

            std::string                 _name;

            OpenThreads::Mutex          _childrenToDeleteListMutex;
            ObjectList                  _childrenToDeleteList;
        };

        // forward declare inner helper classes
        class FindCompileableGLObjectsVisitor;
        friend class FindCompileableGLObjectsVisitor;

        struct DatabasePagerCompileCompletedCallback;
        friend struct DatabasePagerCompileCompletedCallback;

        class FindPagedLODsVisitor;
        friend class FindPagedLODsVisitor;

        struct SortFileRequestFunctor;
        friend struct SortFileRequestFunctor;

        
        OpenThreads::Mutex              _run_mutex;
        bool                            _startThreadCalled;

        // Helper functions for determining if objects need to be
        // compiled.
        inline static bool isCompiled(const osg::Texture* texture,
                                      unsigned int contextID)
        {
            return( texture->getTextureObject(contextID) != NULL );
        }
        // Is texture compiled for all active contexts?
        inline bool isCompiled(osg::Texture* texture) const
        {
            for (ActiveGraphicsContexts::const_iterator iter=_activeGraphicsContexts.begin();
                   iter!=_activeGraphicsContexts.end(); ++iter )
            {
                if ( texture->getTextureObject(*iter) == NULL ) return false;
            }
            return true;
        }
        
        inline static bool isCompiled(const osg::StateSet* stateSet,
                                      unsigned int contextID)
        {
            for (unsigned i = 0;
                 i < stateSet->getTextureAttributeList().size();
                 ++i)
            {
                const osg::Texture* texture
                    = dynamic_cast<const osg::Texture*>(stateSet->getTextureAttribute(i,osg::StateAttribute::TEXTURE));
                if (texture && !isCompiled(texture, contextID))
                    return false;
            }
            return true;
        }

        inline bool isCompiled(osg::StateSet* stateSet)
        {
            for (unsigned i = 0;
                 i < stateSet->getTextureAttributeList().size();
                 ++i)
            {
                osg::Texture* texture
                    = dynamic_cast<osg::Texture*>(stateSet->getTextureAttribute(i,osg::StateAttribute::TEXTURE));
                if (texture)
                {
                    for (ActiveGraphicsContexts::iterator iter=_activeGraphicsContexts.begin();
                            iter!=_activeGraphicsContexts.end(); ++iter )
                    {
                        if ( texture->getTextureObject(*iter) == NULL ) return false;
                    }
                }
            }
            return true;
        }
        
        inline static bool isCompiled(const osg::Drawable* drawable,
                                      unsigned int contextID)
        {
            if (drawable->getUseVertexBufferObjects())
            {
                // say it's not compiled leaving it up to the compileGLObjects() to handle.
                return false;
            }
            else if (drawable->getUseDisplayList())
            {
                return drawable->getDisplayList(contextID) != 0;
            }

            return true;
        }

        inline bool isCompiled(const osg::Drawable* drawable) const
        {
            if (drawable->getUseVertexBufferObjects())
            {
                // say it's not compiled leaving it up to the compileGLObjects() to handle.
                return false;
            }
            if (drawable->getUseDisplayList())
            {
                for (ActiveGraphicsContexts::const_iterator iter=_activeGraphicsContexts.begin();
                        iter!=_activeGraphicsContexts.end(); ++iter )
                {
                    if ( drawable->getDisplayList(*iter) == 0 ) return false;
                }
            }
            return true;
        }

        void compileCompleted(DatabaseRequest* databaseRequest);

        /** Iterate through the active PagedLOD nodes children removing 
          * children which havn't been visited since specified expiryTime.
          * note, should be only be called from the update thread. */
        virtual void removeExpiredSubgraphs(const osg::FrameStamp &frameStamp);

        /** Add the loaded data to the scene graph.*/
        void addLoadedDataToSceneGraph(const osg::FrameStamp &frameStamp);


        bool                            _done;
        bool                            _acceptNewRequests;
        bool                            _databasePagerThreadPaused;
    
        DatabaseThreadList              _databaseThreads;

        int                             _numFramesActive;
        mutable OpenThreads::Mutex      _numFramesActiveMutex;
        int                             _frameNumber;

        osg::ref_ptr<ReadQueue>         _fileRequestQueue;
        osg::ref_ptr<ReadQueue>         _httpRequestQueue;

         
        osg::ref_ptr<RequestQueue>      _dataToCompileList;

        DrawablePolicy                  _drawablePolicy;

        bool                            _changeAutoUnRef;
        bool                            _valueAutoUnRef;
        bool                            _changeAnisotropy;
        float                           _valueAnisotropy;

        bool                            _deleteRemovedSubgraphsInDatabaseThread;

        osg::ref_ptr<RequestQueue>      _dataToMergeList;
        
        osg::ref_ptr<PagedLODList>      _activePagedLODList;
        osg::ref_ptr<PagedLODList>      _inactivePagedLODList;
        
        unsigned int                    _targetMaximumNumberOfPageLOD;

        double                          _expiryDelay;
        int                             _expiryFrames;

        double                          _releaseDelay;
        int                             _releaseFrames;

        ActiveGraphicsContexts          _activeGraphicsContexts;
        // CompileGraphicsContexts         _compileGraphicsContexts;
        
        bool                            _doPreCompile;
        osg::ref_ptr<osgUtil::IncrementalCompileOperation>  _incrementalCompileOperation;

        double                          _targetFrameRate;
        double                          _minimumTimeAvailableForGLCompileAndDeletePerFrame;
        unsigned int                    _maximumNumOfObjectsToCompilePerFrame;
        
        double                          _minimumTimeToMergeTile;
        double                          _maximumTimeToMergeTile;
        double                          _totalTimeToMergeTiles;
        unsigned int                    _numTilesMerges;
        
        struct CompileOperation : public osg::GraphicsOperation
        {
            CompileOperation(DatabasePager* databasePager);
            
            virtual void operator () (osg::GraphicsContext* context);
            
            osg::observer_ptr<DatabasePager> _databasePager;
        };
};

}

#endif