Various tweaks, enhancements, and optimizations surrounding tile paging

(specifically freeing tiles when we need to remove them from the tile cache.)

src/Scenery/tileentry.cxx

@@ -682,24 +682,16 @@ ssgBranch* FGTileEntry::gen_runway_lights( ssgVertexArray *points,ssgVertexArray
 }
 // ADA
 	
-#ifdef WISH_PLIB_WAS_THREADED // but it isn't
-
-// Schedule tile to be freed/removed
-void FGTileEntry::sched_removal() {
-    global_tile_mgr.ready_to_delete( this );
-}
-
-#endif
-
 
 // Free "n" leaf elements of an ssg tree.  returns the number of
 // elements freed.  An empty branch node is considered a leaf.  This
 // is intended to spread the load of freeing a complex tile out over
 // several frames.
 static int fgPartialFreeSSGtree( ssgBranch *b, int n ) {
+    int num_deletes = 0;
+
     if ( n > 0 ) {
         // we still have some delete budget left
-        int num_deletes = 0;
         for ( int i = 0; i < b->getNumKids(); ++i ) {
             ssgEntity *kid = b->getKid(i);
             if ( kid->isAKindOf( ssgTypeBranch() ) && kid->getRef() <= 1 ) {
@@ -719,10 +711,15 @@ static int fgPartialFreeSSGtree( ssgBranch *b, int n ) {
                 num_deletes++;
             }
         }
-        return num_deletes;
-    } else {
-        return 0;
+        // remove the parent if it is empty
+        if ( b->getNumKids() < 0 ) {
+            ssgDeRefDelete( b );
+            num_deletes++;
+            n--;
+        }
     }
+
+    return num_deletes;
 }
 
 
@@ -767,7 +764,6 @@ bool FGTileEntry::free_tile() {
         // disconnected from the scene graph)
         SG_LOG( SG_TERRAIN, SG_DEBUG, "FREEING terra_transform" );
         if ( fgPartialFreeSSGtree( terra_transform, delete_size ) == 0 ) {
-            ssgDeRefDelete( terra_transform ); // polish off the parent
             free_tracker |= TERRA_NODE;
         }
     } else if ( !(free_tracker & GROUND_LIGHTS) && gnd_lights_transform ) {
@@ -775,7 +771,6 @@ bool FGTileEntry::free_tile() {
         // disconnected from the scene graph)
         SG_LOG( SG_TERRAIN, SG_DEBUG, "FREEING gnd_lights_transform" );
         if ( fgPartialFreeSSGtree( gnd_lights_transform, delete_size ) == 0 ) {
-            ssgDeRefDelete( gnd_lights_transform ); // polish off the parent
             free_tracker |= GROUND_LIGHTS;
         }
     } else if ( !(free_tracker & RWY_LIGHTS) && rwy_lights_transform ) {
@@ -783,7 +778,6 @@ bool FGTileEntry::free_tile() {
 	// disconnected from the scene graph)
         SG_LOG( SG_TERRAIN, SG_DEBUG, "FREEING rwy_lights_transform" );
 	if ( fgPartialFreeSSGtree( rwy_lights_transform, delete_size ) == 0 ) {
-            ssgDeRefDelete( rwy_lights_transform ); // polish off the parent
             free_tracker |= RWY_LIGHTS;
         }
     } else if ( !(free_tracker & LIGHTMAPS) && lightmaps_transform ) {
@@ -792,7 +786,6 @@ bool FGTileEntry::free_tile() {
         // disconnected from the scene graph)
         SG_LOG( SG_TERRAIN, SG_DEBUG, "FREEING lightmaps_transform" );
 	if ( fgPartialFreeSSGtree( lightmaps_transform, delete_size ) == 0 ) {
-            ssgDeRefDelete( lightmaps_transform ); // polish off the parent
             free_tracker |= LIGHTMAPS;
         }
     } else {

src/Scenery/tileentry.hxx

@@ -218,11 +218,6 @@ public:
     // Destructor
     ~FGTileEntry();
 
-#ifdef WISH_PLIB_WAS_THREADED // but it isn't
-    // Schedule tile to be freed/removed
-    void sched_removal();
-#endif
-
     // Clean up the memory used by this tile and delete the arrays
     // used by ssg as well as the whole ssg branch.  This does a
     // partial clean up and exits so we can spread the load across

src/Scenery/tilemgr.cxx

@@ -362,9 +362,25 @@ int FGTileMgr::update( double lon, double lat, double visibility_meters,
 	// cout << "Adding ssg nodes for "
     }
 
-    // cout << "delete queue = " << delete_queue.size() << endl;
     if ( !delete_queue.empty() ) {
-	FGTileEntry* e = delete_queue.front();
+        // cout << "delete queue = " << delete_queue.size() << endl;
+
+        while ( delete_queue.size() > 30 ) {
+            // uh oh, delete queue is blowing up, we aren't clearing
+            // it fast enough.  Let's just panic, well not panic, but
+            // get real serious and agressively free up some tiles so
+            // we don't explode our memory usage.
+
+            SG_LOG( SG_TERRAIN, SG_ALERT,
+                    "Alert: catching up on tile delete queue" );
+
+            FGTileEntry* e = delete_queue.front();
+            while ( !e->free_tile() );
+            delete_queue.pop();
+            delete e;
+        }
+
+        FGTileEntry* e = delete_queue.front();
         if ( e->free_tile() ) {
             delete_queue.pop();
             delete e;