/* 
 * Copyright (c) 2006 Stiftung Deutsches Elektronen-Synchroton, 
 * Member of the Helmholtz Association, (DESY), HAMBURG, GERMANY.
 *
 * THIS SOFTWARE IS PROVIDED UNDER THIS LICENSE ON AN "../AS IS" BASIS. 
 * WITHOUT WARRANTY OF ANY KIND, EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED 
 * TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR PARTICULAR PURPOSE AND 
 * NON-INFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE 
 * FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR 
 * THE USE OR OTHER DEALINGS IN THE SOFTWARE. SHOULD THE SOFTWARE PROVE DEFECTIVE 
 * IN ANY RESPECT, THE USER ASSUMES THE COST OF ANY NECESSARY SERVICING, REPAIR OR 
 * CORRECTION. THIS DISCLAIMER OF WARRANTY CONSTITUTES AN ESSENTIAL PART OF THIS LICENSE. 
 * NO USE OF ANY SOFTWARE IS AUTHORIZED HEREUNDER EXCEPT UNDER THIS DISCLAIMER.
 * DESY HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, 
 * OR MODIFICATIONS.
 * THE FULL LICENSE SPECIFYING FOR THE SOFTWARE THE REDISTRIBUTION, MODIFICATION, 
 * USAGE AND OTHER RIGHTS AND OBLIGATIONS IS INCLUDED WITH THE DISTRIBUTION OF THIS 
 * PROJECT IN THE FILE LICENSE.HTML. IF THE LICENSE IS NOT INCLUDED YOU MAY FIND A COPY 
 * AT HTTP://WWW.DESY.DE/LEGAL/LICENSE.HTM
 */
package org.csstudio.sds.ui;

import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.TimeUnit;

import org.csstudio.sds.util.ExecutionService;
import org.eclipse.swt.widgets.Display;
import org.eclipse.ui.PlatformUI;

/**
 * A thread which bundles property and value changes, that are received from the
 * DAL layer, and forwards them to the SDS models in a single
 * Display.syncExec(). This way we avoid slow downs, that occur on several
 * operating systems, when Display.syncExec() is called very often from
 * background threads.
 * 
 * This thread sleeps for a time, which is below the processing capacity of
 * human eyes and brain - so the user will not feel any delay.
 * 
 * @author Sven Wende
 * 
 */
public final class BundelingThread implements Runnable {
	/**
	 * The singleton instance.
	 */
	private static BundelingThread _instance;

	/**
	 * A queue, which contains runnables that process the events that occured
	 * during the last SLEEP_TIME milliseconds.
	 */
	private Queue<Runnable> _queue;

	/**
	 * Standard constructor.
	 */
	private BundelingThread() {
		_queue = new ConcurrentLinkedQueue<Runnable>();

		ExecutionService.getInstance().getScheduledExecutorService()
				.scheduleAtFixedRate(this, 1000, 10, TimeUnit.MILLISECONDS);
	}

	/**
	 * Gets the singleton instance.
	 * 
	 * @return the singleton instance
	 */
	public static synchronized BundelingThread getInstance() {
		if (_instance == null) {
			_instance = new BundelingThread();
		}

		return _instance;
	}

	/**
	 * {@inheritDoc}.
	 */
	@Override
	public void run() {
		processQueue();
	}

	/**
	 * Process the complete queue.
	 */
	private void processQueue() {
		Display display = Display.getCurrent();

		if (display == null) {
			PlatformUI.getWorkbench().getDisplay().asyncExec(new Runnable() {
				@Override
				public void run() {
					Runnable r;

					while ((r = _queue.poll()) != null) {
						r.run();
					}
				}
			});
		} else {
			Runnable r;

			while ((r = _queue.poll()) != null) {
				r.run();
			}
		}
	}

	/**
	 * Adds the specified runnable to the queue.
	 * 
	 * @param runnable
	 *            the runnable
	 */
	public void addRunnable(final Runnable runnable) {
		_queue.add(runnable);

	}

}