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Integration of HDT with Apache Jena

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/*
 * Extracted from Jena TDB, to avoid the dependency.
 * 
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.rdfhdt.hdtjena.util;

import java.util.Iterator;
import java.util.List;

import org.apache.jena.atlas.iterator.IteratorWrapper;

import org.apache.jena.query.QueryCancelledException;

public class IterAbortable extends IteratorWrapper implements Abortable {
	
	/** Create an abortable iterator, storing it in the killList.
	 *  Just return the input iterator if kilList is null. 
	 */
	public static  Iterator makeAbortable(Iterator iter, List killList)
	{
		if ( killList == null )
			return iter ;
		IterAbortable k = new IterAbortable<>(iter) ;
		killList.add(k) ;
		return k ;
	}

	volatile boolean abortFlag;

	public IterAbortable(Iterator iterator)
	{
		super(iterator) ;
	}

	/** Can call asynchronously at anytime */
	@Override
	public void abort() { 
		abortFlag = true ;
	}

	@Override
	public boolean hasNext()
	{
		if ( abortFlag )
			throw new QueryCancelledException() ;
		return iterator.hasNext() ; 
	}

	@Override
	public T next()
	{
		if ( abortFlag )
			throw new QueryCancelledException() ;
		return iterator.next() ; 
	}
}