/*
 * Copyright (c) 2007, intarsys consulting GmbH
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 *
 * - Neither the name of intarsys nor the names of its contributors may be used
 *   to endorse or promote products derived from this software without specific
 *   prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
package de.intarsys.tools.resourcetracker;

import java.lang.ref.ReferenceQueue;

/**
 * A thread for monitoring a reference queue.
 * <p>
 * This monitor is decoupled from the {@link ResourceTracker} instance to allow
 * for heterogenous resources to be tracked in a single thread.
 * 
 */
public class ResourceFinalizer extends Thread {

	private static ResourceFinalizer DEFAULT;

	synchronized public static ResourceFinalizer get() {
		if (DEFAULT == null) {
			DEFAULT = new ResourceFinalizer();
		}
		return DEFAULT;
	}

	final private ReferenceQueue queue = new ReferenceQueue();

	private boolean started = false;

	public ResourceFinalizer() {
		super("resource finalizer");
		// todo some resources must really be finalized
		// todo invent more intelligent shutdown
		setDaemon(true);
	}

	protected void drainQueue() {
		while (true) {
			IResourceReference ref = (IResourceReference) queue.poll();
			if (ref == null) {
				return;
			} else {
				ref.dispose();
			}
		}
	}

	synchronized protected void ensureStarted() {
		if (started) {
			return;
		}
		start();
	}

	public ReferenceQueue getQueue() {
		return queue;
	}

	@Override
	public void run() {
		while (true) {
			try {
				PhantomResourceReference ref = (PhantomResourceReference) queue
						.remove();
				if (ref != null) {
					ref.dispose();
				}
			} catch (Exception e) {
				return;
			}
		}
	}

	@Override
	public synchronized void start() {
		started = true;
		super.start();
	}

}
