AsyncImage.java

/*******************************************************************************
 * Copyright (c) 2012 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http\://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors\:
 *     IBM Corporation - initial API and implementation
 ******************************************************************************/

package org.eclipse.nebula.widgets.geomap.internal;

import java.net.URL;
import java.net.URLConnection;
import java.util.concurrent.FutureTask;
import java.util.concurrent.atomic.AtomicReference;

import org.eclipse.swt.SWTException;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.graphics.ImageData;
import org.eclipse.swt.widgets.Display;

/**
 * An async image that loads itself in the background on an image-fetcher thread.
 * Once its loaded it will trigger a redraw. Sometimes redraws that 
 * are not really necessary can be triggered, but that is not relevant in terms of
 * performance for this swt-component.
 *
 */
@SuppressWarnings("serial")
class AsyncImage extends AtomicReference<ImageData> implements Runnable {

	private final GeoMapHelper geoMapHelper;
	private final TileRef tile;
	private final String tileUrl;

	private volatile long stamp;
	//        private final AtomicReference<ImageData> imageData = new AtomicReference<ImageData>();
	private Image image = null; // might as well be thread-local

	AsyncImage(GeoMapHelper geoMapHelper, TileRef tile, String tileUrl) {
		this.geoMapHelper = geoMapHelper;
		this.stamp = this.geoMapHelper.zoomStamp.longValue();
		this.tile = tile;
		this.tileUrl = tileUrl;
		this.geoMapHelper.executor.execute(new FutureTask<Boolean>(this, Boolean.TRUE));
	}

	private Runnable removeTileFromCacheRunnable = new Runnable() {
		public void run() {
			AsyncImage.this.geoMapHelper.cache.remove(tile);
		}
	};
	private Runnable tileUpdatedRunnable = new Runnable() {
		public void run() {
			AsyncImage.this.geoMapHelper.tileUpdated(tile);
		}
	};
	
	public void run() {
		if (stamp != this.geoMapHelper.zoomStamp.longValue()) {
			try {
				// here is a race, we just live with.
				if (! this.geoMapHelper.getDisplay().isDisposed()) {
					this.geoMapHelper.getDisplay().asyncExec(removeTileFromCacheRunnable);
				}
			} catch (SWTException e) {
				// ignore
			}
			return;
		}
		try {
			URLConnection con = new URL(tileUrl).openConnection();
			con.setRequestProperty("User-Agent", "org.eclipse.nebula.widgets.geomap.GeoMap");   //$NON-NLS-1$ //$NON-NLS-2$
			set(new ImageData(con.getInputStream()));
			try {
				// here is a race, we just live with.
				if (! this.geoMapHelper.getDisplay().isDisposed()) {
					this.geoMapHelper.getDisplay().asyncExec(tileUpdatedRunnable);
				}
			} catch (SWTException e) {
				// ignore
			}
		} catch (Exception e) {
			//                log.log(Level.SEVERE, "failed to load imagedata from url: " + tileUrl, e);
		}
	}

	public Image getImage(Display display) {
		checkThread(display);
		if (image == null && get() != null) {
			image = new Image(display, get());
		}
		return image;
	}

	public void dispose() {
		checkThread(geoMapHelper.getDisplay());
		if (image != null) {
			image.dispose();
			image = null;
		}
	}

	private void checkThread(Display display) {
		// jdk 1.6 bug from checkWidget still fails here
		if (display.getThread() != Thread.currentThread()) {
			throw new IllegalStateException("Wrong thread to pick up the image"); //$NON-NLS-1$
		}
	}
}