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/*******************************************************************************
 * Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Distribution License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *******************************************************************************/

package org.eclipse.rdf4j.common.iteration;

import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Base class for {@link CloseableIteration}s offering common functionality. This class keeps track of whether
 * the iteration has been closed and handles multiple calls to {@link #close()} by ignoring all but the first
 * call.
 */
public abstract class AbstractCloseableIteration implements CloseableIteration {

	/*-----------*
	 * Variables *
	 *-----------*/

	/**
	 * Flag indicating whether this iteration has been closed.
	 */
	private final AtomicBoolean closed = new AtomicBoolean(false);

	/*---------*
	 * Methods *
	 *---------*/

	/**
	 * Checks whether this CloseableIteration has been closed.
	 * 
	 * @return true if the CloseableIteration has been closed, false otherwise.
	 */
	public final boolean isClosed() {
		return closed.get();
	}

	/**
	 * Calls {@link #handleClose()} upon first call and makes sure this method gets called only once.
	 */
	public final void close()
		throws X
	{
		if (closed.compareAndSet(false, true)) {
			handleClose();
		}
	}

	/**
	 * Called by {@link #close} when it is called for the first time. This method is only called once on each
	 * iteration. By default, this method does nothing.
	 * 
	 * @throws X
	 */
	protected void handleClose()
		throws X
	{
	}
}