Improved tile cache priority scheme.

Use priorities for loading/unloading.
Maintain an expiry time for each tile.
Replaced "cache lock" by "current view" flag.

simgear/scene/tgdb/TileCache.cxx

@@ -1,4 +1,4 @@
-// newcache.cxx -- routines to handle scenery tile caching
+// TileCache.cxx -- routines to handle scenery tile caching
 //
 // Written by Curtis Olson, started December 2000.
 //
@@ -51,10 +51,9 @@ void TileCache::entry_free( long cache_index ) {
     SG_LOG( SG_TERRAIN, SG_DEBUG, "FREEING CACHE ENTRY = " << cache_index );
     TileEntry *tile = tile_cache[cache_index];
     tile->removeFromSceneGraph();
+    tile_cache.erase( cache_index );
 
     delete tile;
-
-    tile_cache.erase( cache_index );
 }
 
 
@@ -84,13 +83,12 @@ bool TileCache::exists( const SGBucket& b ) const {
 }
 
 
-// Return the index of the oldest tile in the cache, return -1 if
+// Return the index of a tile to be dropped from the cache, return -1 if
 // nothing available to be removed.
-long TileCache::get_oldest_tile() {
+long TileCache::get_drop_tile() {
-    // we need to free the furthest entry
     long min_index = -1;
-    double timestamp = 0.0;
     double min_time = DBL_MAX;
+    float priority = FLT_MAX;
 
     tile_map_iterator current = tile_cache.begin();
     tile_map_iterator end = tile_cache.end();
@@ -98,20 +96,27 @@ long TileCache::get_oldest_tile() {
     for ( ; current != end; ++current ) {
         long index = current->first;
         TileEntry *e = current->second;
-        if (e->get_cache_lock())
+        if (( !e->is_current_view() )&&
+            ( e->is_expired(current_time) ))
         {
-            // tile locked to cache => must not be dropped
+            if (e->is_expired(current_time - 1.0)&&
-        }
+                !e->is_loaded())
-        else
+            {
-        if ( e->is_loaded() ) {
+                /* Immediately drop "empty" tiles which are no longer used/requested, and were last requested > 1 second ago...
-            timestamp = e->get_timestamp();
+                 * Allow a 1 second timeout since an empty tiles may just be loaded...
-            if ( timestamp < min_time ) {
+                 */
-                min_time = timestamp;
+                SG_LOG( SG_TERRAIN, SG_DEBUG, "    dropping an unused and empty tile");
+                break;
+            }
+            if (( e->get_time_expired() < min_time )||
+                (( e->get_time_expired() == min_time)&&
+                 ( priority > e->get_priority())))
+            {
+                // drop oldest tile with lowest priority
+                min_time = e->get_time_expired();
+                priority = e->get_priority();
                 min_index = index;
             }
-        } else {
-            SG_LOG( SG_TERRAIN, SG_DEBUG, "loaded = " << e->is_loaded()
-                    << " time stamp = " << e->get_timestamp() );
         }
     }
 
@@ -122,35 +127,19 @@ long TileCache::get_oldest_tile() {
 }
 
 
-// Clear the inner ring flag for all tiles in the cache so that the
+// Clear all flags indicating tiles belonging to the current view
-// external tile scheduler can flag the inner ring correctly.
+void TileCache::clear_current_view()
-void TileCache::clear_inner_ring_flags() {
-    tile_map_iterator current = tile_cache.begin();
-    tile_map_iterator end = tile_cache.end();
-
-    for ( ; current != end; ++current ) {
-        TileEntry *e = current->second;
-        //if ( e->is_loaded() ) {
-            e->set_inner_ring( false );
-        //}
-    }
-}
-
-// Clear all locked flags for all tiles in the cache.
-// (Tiles belonging to the current position are locked to
-//  the cache to prevent them from being dropped).
-void TileCache::clear_cache_lock_flags()
 {
     tile_map_iterator current = tile_cache.begin();
     tile_map_iterator end = tile_cache.end();
 
     for ( ; current != end; ++current ) {
         TileEntry *e = current->second;
-        if (e->get_cache_lock())
+        if (e->is_current_view())
         {
-            // update timestamps for tiles belonging to most recent position
+            // update expiry time for tiles belonging to most recent position
-            e->set_timestamp( current_time );
+            e->update_time_expired( current_time );
-            e->set_cache_lock( false );
+            e->set_current_view( false );
         }
     }
 }
@@ -190,8 +179,31 @@ bool TileCache::insert_tile( TileEntry *e ) {
     // register tile in the cache
     long tile_index = e->get_tile_bucket().gen_index();
     tile_cache[tile_index] = e;
-    e->set_timestamp(current_time);
+    e->update_time_expired(current_time);
 
     return true;
 }
 
+// update tile's priority and expiry time according to current request
+void TileCache::request_tile(TileEntry* t,float priority,bool current_view,double request_time)
+{
+    if ((!current_view)&&(request_time<=0.0))
+        return;
+
+    // update priority when hire - or old has expired
+    if ((t->is_expired(current_time))||
+         (priority > t->get_priority()))
+    {
+        t->set_priority( priority );
+    }
+
+    if (current_view)
+    {
+        t->update_time_expired( current_time );
+        t->set_current_view( true );
+    }
+    else
+    {
+        t->update_time_expired( current_time+request_time );
+    }
+}

simgear/scene/tgdb/TileCache.hxx

@@ -1,4 +1,4 @@
-// newcache.hxx -- routines to handle scenery tile caching
+// TileCache.hxx -- routines to handle scenery tile caching
 //
 // Written by Curtis Olson, started December 2000.
 //
@@ -49,11 +49,11 @@ private:
     // pointers to allow an external linear traversal of cache entries
     tile_map_iterator current;
 
+    double current_time;
+
     // Free a tile cache entry
     void entry_free( long cache_index );
 
-    double current_time;
-
 public:
     tile_map_iterator begin() { return tile_cache.begin(); }
     tile_map_iterator end() { return tile_cache.end(); }
@@ -72,18 +72,12 @@ public:
     // Check if the specified "bucket" exists in the cache
     bool exists( const SGBucket& b ) const;
 
-    // Return the index of the oldest tile in the cache, return -1 if
+    // Return the index of a tile to be dropped from the cache, return -1 if
     // nothing available to be removed.
-    long get_oldest_tile();
+    long get_drop_tile();
-
+    
-    // Clear the inner ring flag for all tiles in the cache so that
+    // Clear all flags indicating tiles belonging to the current view
-    // the external tile scheduler can flag the inner ring correctly.
+    void clear_current_view();
-    void clear_inner_ring_flags();
-
-    // Clear all locked flags for all tiles in the cache.
-    // (Tiles belonging to the current position are locked to
-    //  the cache to prevent them from being dropped).
-    void clear_cache_lock_flags();
 
     // Clear a cache entry, note that the cache only holds pointers
     // and this does not free the object which is pointed to.
@@ -131,6 +125,9 @@ public:
 
     void set_current_time(double val) { current_time = val; }
     double get_current_time() const { return current_time; }
+
+    // update tile's priority and expiry time according to current request
+    void request_tile(TileEntry* t,float priority,bool current_view,double requesttime);
 };
 
 }

simgear/scene/tgdb/TileEntry.cxx

@@ -64,77 +64,16 @@ osgDB::RegisterReaderWriterProxy<ReaderWriterSTG> g_readerWriterSTGProxy;
 ModelRegistryCallbackProxy<LoadOnlyCallback> g_stgCallbackProxy("stg");
 }
 
-#ifdef USE_CULLCALLBACK_TS
-namespace
-{
-// Update the timestamp on a tile whenever it is in view.
-
-class TileCullCallback : public osg::NodeCallback
-{
-public:
-    TileCullCallback() : _timeStamp(0) {}
-    TileCullCallback(const TileCullCallback& tc, const osg::CopyOp& copyOp) :
-        NodeCallback(tc, copyOp), _timeStamp(tc._timeStamp)
-    {
-    }
-
-    virtual void operator()(osg::Node* node, osg::NodeVisitor* nv);
-    double getTimeStamp() const { return _timeStamp; }
-    void setTimeStamp(double timeStamp) { _timeStamp = timeStamp; }
-protected:
-    double _timeStamp;
-};
-}
-
-void TileCullCallback::operator()(osg::Node* node, osg::NodeVisitor* nv)
-{
-    if (nv->getFrameStamp())
-        _timeStamp = nv->getFrameStamp()->getReferenceTime();
-    traverse(node, nv);
-}
-#endif
-
-double TileEntry::get_timestamp() const
-{
-#ifdef USE_CULLCALLBACK_TS
-    if (_node.valid()) {
-        return (dynamic_cast<TileCullCallback*>(_node->getCullCallback()))
-            ->getTimeStamp();
-    } else
-        return DBL_MAX;
-#else
-    return timestamp;
-#endif
-}
-
-void TileEntry::set_timestamp(double time_ms)
-{
-#ifdef USE_CULLCALLBACK_TS
-    if (_node.valid()) {
-        TileCullCallback* cb
-            = dynamic_cast<TileCullCallback*>(_node->getCullCallback());
-        if (cb)
-            cb->setTimeStamp(time_ms);
-    }
-#else
-    timestamp = time_ms;
-#endif
-}
 
 // Constructor
 TileEntry::TileEntry ( const SGBucket& b )
     : tile_bucket( b ),
       tileFileName(b.gen_index_str()),
       _node( new osg::LOD ),
-      is_inner_ring(false)
+      _priority(-FLT_MAX),
-      ,is_cache_locked(false)
+      _current_view(false),
-#ifndef USE_CULLCALLBACK_TS
+      _time_expired(-1.0)
-      ,timestamp(0.0)
-#endif
 {
-#ifdef USE_CULLCALLBACK_TS
-    _node->setCullCallback(new TileCullCallback);
-#endif
     tileFileName += ".stg";
     _node->setName(tileFileName);
     // Give a default LOD range so that traversals that traverse
@@ -462,4 +401,3 @@ TileEntry::removeFromSceneGraph()
         }
     }
 }
-

simgear/scene/tgdb/TileEntry.hxx

@@ -74,15 +74,16 @@ private:
                           const osgDB::ReaderWriter::Options* options);
 
     /**
-     * this value is used by the tile scheduler/loader to mark which
+     * This value is used by the tile scheduler/loader to load tiles
-     * tiles are in the primary ring (i.e. the current tile or the
+     * in a useful sequence. The priority is set to reflect the tiles
-     * surrounding eight.)  Other routines then can use this as an
+     * distance from the center, so all tiles are loaded in an innermost
-     * optimization and not do some operation to tiles outside of this
+     * to outermost sequence.
-     * inner ring.  (For instance vasi color updating)
      */
-    bool is_inner_ring;
+    float _priority;
-    bool is_cache_locked;
+    /** Flag indicating if tile belongs to current view. */ 
-    double timestamp;
+    bool _current_view;
+    /** Time when tile expires. */ 
+    double _time_expired;
 
     static ModelLoadHelper *_modelLoader;
 
@@ -136,13 +137,19 @@ public:
      */
     osg::LOD *getNode() const { return _node.get(); }
 
-    double get_timestamp() const;
+    inline double get_time_expired() const { return _time_expired; }
-    void set_timestamp( double time_ms );
+    inline void update_time_expired( double time_expired ) { if (_time_expired<time_expired) _time_expired = time_expired; }
 
-    inline bool get_inner_ring() const { return is_inner_ring; }
+    inline void set_priority(float priority) { _priority=priority; }
-    inline void set_inner_ring( bool val ) { is_inner_ring = val; }
+    inline float get_priority() const { return _priority; }
-    inline void set_cache_lock( bool val ) { is_cache_locked = val; }
+    inline void set_current_view(bool current_view) { _current_view = current_view; }
-    inline bool get_cache_lock() const { return is_cache_locked; }
+    inline bool is_current_view() const { return _current_view; }
+
+    /**
+     * Return true if the tile entry is still needed, otherwise return false
+     * indicating that the tile is no longer in active use.
+     */
+    inline bool is_expired(double current_time) const { return (_current_view) ? false : (current_time > _time_expired); }
 
     // Get the ref_ptr to the DatabaseRequest object, in order to pass
     // this to the pager.