Using threads in tile loaders

Programmer's documentation > Programming with JViews Maps > Creating a map application using the API > Using threads in tile loaders

When tiles are displayed on a view, the tile loading is performed for the IlvTiledLayer s by an IlvTileLoader, mainly through the call of the load method. Up until JViews Maps 8.1, this was performed in the Swing thread, which could cause GUI freezes because the code could be CPU intensive.

You can execute the tile loading code in separate threads by means of the IlvThreadedTileLoader class. This class implements the IlvTileLoader interface, and acts as a wrapper for a delegate IlvTileLoader executing the tile loading code.

Internally, an IlvThreadedTileLoader object holds a queue in which load and release calls (from the IlvTileController on the IlvThreadedTileLoader ) are stacked, and processed as soon as possible by a dedicated thread. This way, all tile loading is performed asynchronously and the application remains responsive even if tens of megabytes of data are loaded for display on the view.

The source code for the Map Builder demonstration, which contains all of the code described in this section, can be found at <installdir> /jviews-maps/samples/mapbuilder/index.html

The following code sample shows how to use an IlvThreadedTileLoader that encapsulates another tile loader:

IlvTiledLayer tiledLayer;

// this is the tile loader that performs the real loading, such as

IlvShapeFileTileLoader

IlvTileLoader tileLoader;

// Create a threaded tile loader that encapsulates the previous one

IlvThreadedTileLoader threadedTileLoader =

new IlvThreadedTileLoader(tileLoader,true);

// Configure this threaded tile loader:

// set the minimum java thread priority for loading tiles

threadedTileLoader.setThreadPriority(Thread.MIN_PRIORITY);

// set to repaint the view after each tile is loaded

threadedTileLoader.setRepaintPolicy(IlvThreadedTileLoader.REPAINT_AFTER_EACH_TI

LE);

// Set this threaded tile loader on the IlvTiledLayer

tiledLayer.setTileLoader(threadedTileLoader);