Tweaks to the tile pager so it waits for a signal from the main thread before

loading the next tile.  This allows the main thread to "pace" the tile loader
so it consumes fewer resources.

src/Scenery/FGTileLoader.cxx

@@ -50,7 +50,7 @@ FGTileLoader::~FGTileLoader()
 {
 #ifdef ENABLE_THREADS
     // Wake up its time to die.
-    cond.broadcast();
+    queue_cond.broadcast();
 
     for (int i = 0; i < MAX_THREADS; ++i)
     {
@@ -86,13 +86,27 @@ FGTileLoader::add( FGTileEntry* tile )
     mutex.lock();
     tile_queue.push( tile );
     // Signal waiting working threads.
-    cond.signal();
+    queue_cond.signal();
     mutex.unlock();
 #else
     tile->load( tile_path, true );
 #endif // ENABLE_THREADS
 }
 
+/**
+ * 
+ */
+void
+FGTileLoader::update()
+{
+#ifdef ENABLE_THREADS
+    mutex.lock();
+    frame_cond.signal();
+    mutex.unlock();
+#endif // ENABLE_THREADS
+}
+
+
 #ifdef ENABLE_THREADS
 /**
  * 
@@ -106,7 +120,7 @@ FGTileLoader::LoaderThread::run()
 	loader->mutex.lock();
 	while (loader->empty())
 	{
-	    loader->cond.wait( loader->mutex );
+	    loader->queue_cond.wait( loader->mutex );
 	}
 
 	// Have we been canceled - exits if yes.
@@ -117,6 +131,10 @@ FGTileLoader::LoaderThread::run()
 	    pthread_exit( PTHREAD_CANCELED );
 	}
 
+        // Wait for the next frame signal before we load a tile from the queue
+        // Note that loader->mutex is already locked at this point.
+        loader->frame_cond.wait( loader->mutex );
+
 	// Grab the tile to load and release the mutex.
 	FGTileEntry* tile = loader->tile_queue.front();
 	loader->tile_queue.pop();

src/Scenery/FGTileLoader.hxx

@@ -61,6 +61,14 @@ public:
      */
     void add( FGTileEntry* tile );
 
+    /**
+     * The tile loader thread will only load one tile per call to the
+     * update() method.  This is a way to spread out the work of the
+     * tile loader and slow it down so it is less intrusive.  For
+     * systems built without thead support this is a no-op.
+     */
+    void update();
+
     /**
      * Returns whether the load queue is empty (contains no elements).
      * @return true if load queue is empty otherwise returns false.
@@ -123,7 +131,8 @@ private:
      * Lock and synchronize access to tile queue.
      */
     SGMutex mutex;
-    SGCondition cond;
+    SGCondition queue_cond;
+    SGCondition frame_cond;
 
     /**
      * Thread cleanup handler.

src/Scenery/newcache.cxx

@@ -212,18 +212,13 @@ void FGNewCache::make_space() {
  * Create a new tile and schedule it for loading.
  */
 void
-FGNewCache::load_tile( const SGBucket& b )
+FGNewCache::insert_tile( FGTileEntry *e )
 {
     // clear out a distant entry in the cache if needed.
     make_space();
 
-    // create the entry
-    FGTileEntry *e = new FGTileEntry( b );
-
     // register it in the cache
-    long tile_index = b.gen_index();
+    long tile_index = e->get_tile_bucket().gen_index();
     tile_cache[tile_index] = e;
 
-    // Schedule tile for loading
-    loader.add( e );
 }

src/Scenery/newcache.hxx

@@ -46,7 +46,6 @@
 #include <simgear/math/point3d.hxx>
 
 #include "tileentry.hxx"
-#include "FGTileLoader.hxx"
 
 SG_USING_STD(map);
 
@@ -69,11 +68,6 @@ class FGNewCache {
     // Free a tile cache entry
     void entry_free( long cache_index );
 
-    /**
-     * Queue tiles for loading.
-     */
-    FGTileLoader loader;
-
 public:
 
     // Constructor
@@ -128,7 +122,7 @@ public:
      * Create a new tile and enqueue it for loading.
      * @param b 
      */
-    void load_tile( const SGBucket& b );
+    void insert_tile( FGTileEntry* e );
 };
 
 

src/Scenery/tileentry.hxx

@@ -165,7 +165,13 @@ public:
      * Return true if the tile entry is loaded, otherwise return false
      * indicating that the loading thread is still working on this.
      */
-   inline bool is_loaded() const { return loaded; }
+    inline bool is_loaded() const { return loaded; }
+
+    /**
+     * Return the "bucket" for this tile
+     */
+    inline SGBucket get_tile_bucket() const { return tile_bucket; }
+
 };
 
 

src/Scenery/tilemgr.cxx

@@ -116,8 +116,14 @@ void FGTileMgr::sched_tile( const SGBucket& b ) {
     FGTileEntry *t = tile_cache.get_tile( b );
 
     if ( t == NULL ) {
-        // register a load request
-	tile_cache.load_tile( b );
+        // create a new entry
+        FGTileEntry *e = new FGTileEntry( b );
+
+        // insert the tile into the cache
+	tile_cache.insert_tile( e );
+
+        // Schedule tile for loading
+        loader.add( e );
     }
 }
 
@@ -271,8 +277,6 @@ void FGTileMgr::initialize_queue()
     SG_LOG( SG_TERRAIN, SG_INFO, "Updating Tile list for " << current_bucket );
     // cout << "tile cache size = " << tile_cache.get_size() << endl;
 
-    int i;
-
     // wipe/initialize tile cache
     // tile_cache.init();
     previous_bucket.make_bad();
@@ -288,6 +292,7 @@ void FGTileMgr::initialize_queue()
 #if 0
     // Now force a load of the center tile and inner ring so we
     // have something to see in our first frame.
+    int i;
     for ( i = 0; i < 9; ++i ) {
         if ( load_queue.size() ) {
             SG_LOG( SG_TERRAIN, SG_DEBUG, 
@@ -402,6 +407,13 @@ int FGTileMgr::update( double lon, double lat ) {
     last_longitude = longitude;
     last_latitude  = latitude;
 
+    // activate loader thread one out of every 5 frames
+    counter_hack = (counter_hack + 1) % 5;
+    if ( !counter_hack ) {
+        // Notify the tile loader that it can load another tile
+        loader.update();
+    }
+
     return 1;
 }
 

src/Scenery/tilemgr.hxx

@@ -35,6 +35,7 @@
 
 #include <simgear/bucket/newbucket.hxx>
 
+#include "FGTileLoader.hxx"
 #include "hitlist.hxx"
 #include "newcache.hxx"
 
@@ -102,10 +103,16 @@ private:
     double last_latitude;
 
     /**
-     * 
+     * tile cache
      */
     FGNewCache tile_cache;
 
+    /**
+     * Queue tiles for loading.
+     */
+    FGTileLoader loader;
+    int counter_hack;
+
 public:
 
     // Constructor