We can't remove ssg branches in the threaded tile page because if we happen

to have attached an ssg loaded object to this branch, then plib will remove
it and all it's states (and textures) which will call opengl api commands
which will crash the program if run from a separate thread from the main render
thread.

src/Scenery/FGTileLoader.cxx

@@ -89,6 +89,7 @@ FGTileLoader::add( FGTileEntry* tile )
     tile_load_queue.push( tile );
 }
 
+#ifdef WISH_PLIB_WAS_THREADED // but it isn't
 /**
  * 
  */
@@ -97,6 +98,7 @@ FGTileLoader::remove( FGTileEntry* tile )
 {
     tile_free_queue.push( tile );
 }
+#endif
 
 /**
  * 
@@ -156,6 +158,7 @@ FGTileLoader::LoaderThread::run()
 
   	FGTileMgr::ready_to_attach( tile );
 
+#ifdef WISH_PLIB_WAS_THREADED // but it isn't
 	// Handle and pending removals
 	while ( !loader->tile_free_queue.empty() ) {
 	    cout << "freeing next tile ..." << endl;
@@ -164,6 +167,8 @@ FGTileLoader::LoaderThread::run()
 	    tile->free_tile();
 	    delete tile;
 	}
+#endif
+
     }
     pthread_cleanup_pop(1);
 }

src/Scenery/FGTileLoader.hxx

@@ -60,11 +60,13 @@ public:
      */
     void add( FGTileEntry* tile );
 
+#ifdef WISH_PLIB_WAS_THREADED // but it isn't
     /**
      * Remove a tile from memory.
      * @param tile The tile to be removed from memory.
      */
     void remove( FGTileEntry* tile );
+#endif
 
     /**
      * The tile loader thread will only load one tile per call to the
@@ -89,10 +91,10 @@ private:
      * FIFO queue of tiles to load from data files.
      */
     SGBlockingQueue< FGTileEntry * > tile_load_queue;
-    SGBlockingQueue< FGTileEntry * > tile_free_queue;
+    // SGBlockingQueue< FGTileEntry * > tile_free_queue;
 #else
     queue< FGTileEntry * > tile_load_queue;
-    queue< FGTileEntry * > tile_free_queue;
+    // queue< FGTileEntry * > tile_free_queue;
 #endif
 
     /**

src/Scenery/newcache.cxx

@@ -64,9 +64,10 @@ void FGNewCache::entry_free( long cache_index ) {
     SG_LOG( SG_TERRAIN, SG_DEBUG, "FREEING CACHE ENTRY = " << cache_index );
     FGTileEntry *tile = tile_cache[cache_index];
     tile->disconnect_ssg_nodes();
-    tile->sched_removal();
 
-#if 0
+#ifdef WISH_PLIB_WAS_THREADED
+    tile->sched_removal();
+#else // plib isn't threaded so we always go here
     tile->free_tile();
     delete tile;
 #endif

src/Scenery/tileentry.cxx

@@ -105,11 +105,15 @@ static void my_remove_branch( ssgBranch * branch ) {
 }
 
 
+#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
+
 
 // Clean up the memory used by this tile and delete the arrays used by
 // ssg as well as the whole ssg branch

src/Scenery/tileentry.hxx

@@ -177,8 +177,10 @@ 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

src/Scenery/tilemgr.hxx

@@ -143,10 +143,12 @@ public:
      */
     static void ready_to_attach( FGTileEntry *t ) { attach_queue.push( t ); }
 
+#ifdef WISH_PLIB_WAS_THREADED // but it isn't
     /**
      * Tile is detatched from scene graph and is ready to delete
      */
     inline void ready_to_delete( FGTileEntry *t ) { loader.remove( t ); }
+#endif
 
     /**
      * Add a pending model to the 'deferred model load' queue