EDTExecutor.java

/*
ALMA - Atacama Large Millimiter Array
* Copyright (c) European Southern Observatory, 2012 
* 
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
* 
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
* 
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
*/
package alma.acs.gui.util.threadsupport;

import java.lang.reflect.InvocationTargetException;
import java.util.List;
import java.util.concurrent.AbstractExecutorService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;

import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;

/**
 * <code>EDTExecutor</code> executes tasks in the swing event dispatcher thread (EDT).
 * <P>
 * <code>EDTExecutor</code> is a helper that allows to submit tasks to the EDT like 
 * {@link SwingUtilities#invokeLater(Runnable)} does. The advantage is that it handles the case
 * of executing the code from inside or outside of the EDT in a transparent way.
 * <BR>
 * In the same way, <code>EDTExecutor</code> allows to run commands synchronously inside the EDT 
 * in the same way {@link SwingUtilities#invokeAndWait(Runnable)} does.
 * <P>
 * {@link SwingWorker} has something in common with <code>EDTExecutor</code> but it is too heavy
 * and for most applications we don't need such a complexity.
 * <P>
 * We don't really need <code>EDTExecutor</code> to be a {@link ExecutorService} because it
 * is very easy but in future we might want to extend by adding more features 
 * (without reaching the same completeness of {@link SwingWorker} of course).
 * <P>
 * Life cycle methods are kept easy because this class does not manage the life cycle of the EDT.
 * In this perspective, and to avoid useless blocking due to synchronization, <code>EDTExecutor</code> 
 * does not keep track of tasks scheduled to be run and not yet executed (@see {@link #shutdownNow()}.  
 * 
 * @author  acaproni
 * @since ACS 10.2
 */
public class EDTExecutor extends AbstractExecutorService {
	
	/**
	 * The singleton
	 */
	private static final EDTExecutor executor = new EDTExecutor();
	
	/**
	 * A flag set is the executor has been shut down.
	 */
	protected volatile boolean hasBeenShutdown=false;
	
	/**
	 * The constructor is private because it is a singleton.
	 */
	private EDTExecutor() {}
	
	/**
	 * 
	 * @return The singleton
	 */
	public static EDTExecutor instance() {
		return executor;
	}

	/**
	 * Shuts down the Executor (and not the swing EDT): 
	 * <code>EDTExecutor</code> will not submit other tasks to the EDT.
	 * 
	 * 
	 */
	@Override
	public void shutdown() {
		hasBeenShutdown=true;
	}

	/**
	 * Shuts down the Executor (and not the swing EDT): 
	 * <code>EDTExecutor</code> will not submit other tasks to the EDT.
	 * 
	 * @return <code>null</code> because this executor does not have a queue of tasks to submit.
	 */
	@Override
	public List<Runnable> shutdownNow() {
		hasBeenShutdown=true;
		return null;
	}

	@Override
	public boolean isShutdown() {
		return hasBeenShutdown;
	}

	@Override
	public synchronized boolean isTerminated() {
		return hasBeenShutdown;
	}

	@Override
	public boolean awaitTermination(long timeout, TimeUnit unit)
			throws InterruptedException {
		if (isTerminated()) {
			return true;
		}
		// Wait until the timeout elapses (or a InterruptedExceprtion occurs) 
		// and check again
		boolean ret;
		try {
			unit.sleep(timeout);
		} catch (InterruptedException ie) {			
		} finally {
			ret=isTerminated();
		}
		return ret;
	}

	/**
	 * Executes the passed command in the EDT.
	 * <P>
	 * It can be called from inside or outside of the swing event dispatcher thread.
	 * 
	 * @param command The command to execute in the EDT
	 */
	@Override
	public void execute(Runnable command) {
		if (command==null) {
			// Nothing to run!
			return;
		}
		if (hasBeenShutdown) {
			// Do not accept further commands
			return;
		}
		if (SwingUtilities.isEventDispatchThread()) {
			command.run();
		} else {
			SwingUtilities.invokeLater(command);
		}
	}
	
	/**
	 * Execute the passed command in the EDT synchronously.
	 * <P>
	 * It can be called from inside or outside of the swing event dispatcher thread.
	 * 
	 * @param command The command to execute in the EDT
	 * 
	 * @throws InvocationTargetException if an exception is thrown while running the <code>command</code>
	 * @throws InterruptedException if we're interrupted while waiting for the event dispatching thread to finish excecuting <code>command.run()</code>
	 */
	public void executeSync(Runnable command) throws InvocationTargetException, InterruptedException {
		if (command==null) {
			// Nothing to run!
			return;
		}
		if (hasBeenShutdown) {
			// Do not accept further commands
			return;
		}

		if (SwingUtilities.isEventDispatchThread()) {
			command.run();
		} else {
			SwingUtilities.invokeAndWait(command);
		}
	}
}