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A federation engine for virtually integrating SPARQL endpoints

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/*******************************************************************************
 * Copyright (c) 2019 Eclipse RDF4J contributors.
 *
 * 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.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 *******************************************************************************/
package org.eclipse.rdf4j.federated.evaluation.join;

import org.eclipse.rdf4j.common.iteration.CloseableIteration;
import org.eclipse.rdf4j.federated.evaluation.FederationEvalStrategy;
import org.eclipse.rdf4j.federated.structures.QueryInfo;
import org.eclipse.rdf4j.query.BindingSet;
import org.eclipse.rdf4j.query.QueryEvaluationException;
import org.eclipse.rdf4j.query.algebra.TupleExpr;

/**
 * Execute the nested loop join in a synchronous fashion, i.e. one binding after the other
 *
 * @author Andreas Schwarte
 */
public class SynchronousJoin extends JoinExecutorBase {

	public SynchronousJoin(FederationEvalStrategy strategy,
			CloseableIteration leftIter,
			TupleExpr rightArg, BindingSet bindings, QueryInfo queryInfo)
			throws QueryEvaluationException {
		super(strategy, leftIter, rightArg, bindings, queryInfo);
	}

	@Override
	protected void handleBindings() throws Exception {

		int totalBindings = 0;

		while (!isClosed() && leftIter.hasNext()) {
			rightQueue.put(strategy.evaluate(rightArg, leftIter.next()));
			totalBindings++;
		}

		if (log.isDebugEnabled()) {
			log.debug("JoinStats: left iter of " + getDisplayId() + " had " + totalBindings + " results.");
		}
	}
}