/*******************************************************************************
 * Copyright (c) 2007, 2010 Association for Decentralized Information Management
 * in Industry THTH ry.
 * 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:
 *     VTT Technical Research Centre of Finland - initial API and implementation
 *******************************************************************************/

package org.simantics.utils.threads.ua;

import java.util.ArrayDeque;
import java.util.Queue;
import java.util.concurrent.Executor;

/**
 * The executor serializes the submission of tasks to a second executor,
 * illustrating a composite executor.
 * 
 * (This code is copied from the example in {@link Executor})
 */
public class SerialExecutor implements Executor {
    final Queue<Runnable> tasks = new ArrayDeque<Runnable>();
    final Executor executor;
    Runnable active;
		 
    public SerialExecutor(Executor executor) {
        this.executor = executor;
    }
		 
    public synchronized void execute(final Runnable r) {
        tasks.offer(new Runnable() {
            public void run() {
                try {
                    r.run();
                } finally {
                    scheduleNext();
                }
            }
        });
        if (active == null) {
            scheduleNext();
        }
    }
		 
    protected synchronized void scheduleNext() {
        if ((active = tasks.poll()) != null) {
            executor.execute(active);
        }
    }
	
}