GH-4894 revert code that is still in use by our users

Author: hmottestad

core/common/iterator/src/main/java/org/eclipse/rdf4j/common/iteration/ThreadSafeDelayedIteration.java

@@ -0,0 +1,121 @@
+/*******************************************************************************
+ * Copyright (c) 2024 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.common.iteration;
+
+import java.util.NoSuchElementException;
+
+/**
+ * An iteration that delays the creation of the underlying iteration until it is being accessed. This is mainly useful
+ * for situations where iteration creation adds considerable overhead but where the iteration may not actually be used,
+ * or where a created iteration consumes scarce resources like JDBC-connections or memory. Subclasses must implement the
+ * <var>createIteration</var> method, which is called once when the iteration is first needed.
+ */
+public abstract class ThreadSafeDelayedIteration<E> extends AbstractCloseableIteration<E> {
+
+	/*-----------*
+	 * Variables *
+	 *-----------*/
+
+	private volatile CloseableIteration<? extends E> iter;
+
+	/*--------------*
+	 * Constructors *
+	 *--------------*/
+
+	/**
+	 * Creates a new DelayedIteration.
+	 */
+	protected ThreadSafeDelayedIteration() {
+		super();
+	}
+
+	/*---------*
+	 * Methods *
+	 *---------*/
+
+	/**
+	 * Creates the iteration that should be iterated over. This method is called only once, when the iteration is first
+	 * needed.
+	 */
+	protected abstract CloseableIteration<? extends E> createIteration();
+
+	/**
+	 * Calls the <var>hasNext</var> method of the underlying iteration.
+	 */
+	@Override
+	public boolean hasNext() {
+		if (isClosed()) {
+			return false;
+		}
+		CloseableIteration<? extends E> resultIter = iter;
+		if (resultIter == null) {
+			synchronized (this) {
+				resultIter = iter;
+				if (resultIter == null) {
+					// Underlying iterator has not yet been initialized
+					resultIter = iter = createIteration();
+				}
+			}
+		}
+
+		return resultIter.hasNext();
+	}
+
+	/**
+	 * Calls the <var>next</var> method of the underlying iteration.
+	 */
+	@Override
+	public E next() {
+		if (isClosed()) {
+			throw new NoSuchElementException("Iteration has been closed");
+		}
+		CloseableIteration<? extends E> resultIter = iter;
+		if (resultIter == null) {
+			synchronized (this) {
+				resultIter = iter;
+				if (resultIter == null) {
+					// Underlying iterator has not yet been initialized
+					resultIter = iter = createIteration();
+				}
+			}
+		}
+
+		return resultIter.next();
+	}
+
+	/**
+	 * Calls the <var>remove</var> method of the underlying iteration.
+	 */
+	@Override
+	public void remove() {
+		if (isClosed()) {
+			throw new IllegalStateException("The iteration has been closed.");
+		}
+		CloseableIteration<? extends E> resultIter = iter;
+		if (resultIter == null) {
+			throw new IllegalStateException("Underlying iteration was null");
+		}
+
+		resultIter.remove();
+	}
+
+	/**
+	 * Closes this iteration as well as the underlying iteration if it has already been created and happens to be a
+	 * {@link CloseableIteration}.
+	 */
+	@Override
+	protected void handleClose() {
+		if (iter != null) {
+			iter.close();
+		}
+	}
+}

core/model/src/main/java/org/eclipse/rdf4j/model/impl/GenericStatement.java

@@ -48,7 +48,7 @@ public class GenericStatement<R extends Resource, I extends IRI, V extends Value
 	 * @param object    The statement's object, must not be <var>null</var>.
 	 * @param context   The statement's context, <var>null</var> to indicate no context is associated.
 	 */
-	protected GenericStatement(R subject, I predicate, V object, R context) {
+	public GenericStatement(R subject, I predicate, V object, R context) {
 		this.subject = Objects.requireNonNull(subject, "subject must not be null");
 		this.predicate = Objects.requireNonNull(predicate, "predicate must not be null");
 		this.object = Objects.requireNonNull(object, "object must not be null");

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/impl/DefaultEvaluationStrategy.java

@@ -212,7 +212,7 @@ public class DefaultEvaluationStrategy implements EvaluationStrategy, FederatedS
 
 	private Supplier<CollectionFactory> collectionFactory = DefaultCollectionFactory::new;
 
-	static CloseableIteration<BindingSet> evaluate(TupleFunction func,
+	protected static CloseableIteration<BindingSet> evaluate(TupleFunction func,
 			final List<Var> resultVars, final BindingSet bindings, ValueFactory valueFactory, Value... argValues)
 			throws QueryEvaluationException {
 		final CloseableIteration<? extends List<? extends Value>> iter = func

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/optimizer/QueryJoinOptimizer.java

@@ -96,7 +96,7 @@ public QueryJoinOptimizer(EvaluationStatistics statistics, boolean trackResultSi
 	 */
 	@Override
 	public void optimize(TupleExpr tupleExpr, Dataset dataset, BindingSet bindings) {
-		tupleExpr.visit(new JoinVisitor(statistics, trackResultSize, tripleSource));
+		tupleExpr.visit(new JoinVisitor());
 	}
 
 	/**
@@ -105,17 +105,12 @@ public void optimize(TupleExpr tupleExpr, Dataset dataset, BindingSet bindings)
 	@SuppressWarnings("InnerClassMayBeStatic")
 	protected class JoinVisitor extends AbstractSimpleQueryModelVisitor<RuntimeException> {
 
-		private final EvaluationStatistics statistics;
-		private final TripleSource tripleSource;
-		private final boolean trackResultSize;
-		Set<String> boundVars = new HashSet<>();
+		private Set<String> boundVars = new HashSet<>();
 		private double currentHighestCost = 1;
 
-		private JoinVisitor(EvaluationStatistics statistics, boolean trackResultSize, TripleSource tripleSource) {
+		protected JoinVisitor() {
 			super(trackResultSize);
-			this.statistics = statistics;
-			this.tripleSource = tripleSource;
-			this.trackResultSize = trackResultSize;
+
 		}
 
 		@Override
@@ -332,7 +327,7 @@ public void meet(Join node) {
 
 		private void optimizeInNewScope(List<TupleExpr> subSelects) {
 			for (TupleExpr subSelect : subSelects) {
-				subSelect.visit(new JoinVisitor(statistics, trackResultSize, tripleSource));
+				subSelect.visit(new JoinVisitor());
 			}
 		}
 

core/queryalgebra/model/src/main/java/org/eclipse/rdf4j/query/algebra/TupleExpr.java

@@ -39,11 +39,17 @@ public interface TupleExpr extends QueryModelNode {
 	TupleExpr clone();
 
 	@Experimental
-	Set<Var> getSupportedOrders(AvailableStatementOrder tripleSource);
+	default Set<Var> getSupportedOrders(AvailableStatementOrder tripleSource) {
+		return Set.of();
+	}
 
 	@Experimental
-	void setOrder(Var var);
+	default void setOrder(Var var) {
+		throw new UnsupportedOperationException("Ordering is not supported for this TupleExpr");
+	}
 
 	@Experimental
-	Var getOrder();
+	default Var getOrder() {
+		throw new UnsupportedOperationException("Ordering is not supported for this TupleExpr");
+	}
 }

core/queryalgebra/model/src/main/java/org/eclipse/rdf4j/query/algebra/helpers/collectors/BGPCollector.java

@@ -0,0 +1,59 @@
+/*******************************************************************************
+ * Copyright (c) 2024 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.query.algebra.helpers.collectors;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.eclipse.rdf4j.query.algebra.Join;
+import org.eclipse.rdf4j.query.algebra.QueryModelNode;
+import org.eclipse.rdf4j.query.algebra.QueryModelVisitor;
+import org.eclipse.rdf4j.query.algebra.StatementPattern;
+import org.eclipse.rdf4j.query.algebra.helpers.AbstractQueryModelVisitor;
+
+/**
+ * Basic graph pattern collector.
+ */
+public class BGPCollector<X extends Exception> extends AbstractQueryModelVisitor<X> {
+
+	private final QueryModelVisitor<X> visitor;
+
+	private List<StatementPattern> statementPatterns;
+
+	public BGPCollector(QueryModelVisitor<X> visitor) {
+		this.visitor = visitor;
+	}
+
+	public List<StatementPattern> getStatementPatterns() {
+		return (statementPatterns != null) ? statementPatterns : Collections.emptyList();
+	}
+
+	@Override
+	public void meet(Join node) throws X {
+		// by-pass meetNode()
+		node.visitChildren(this);
+	}
+
+	@Override
+	public void meet(StatementPattern sp) throws X {
+		if (statementPatterns == null) {
+			statementPatterns = new ArrayList<>();
+		}
+		statementPatterns.add(sp);
+	}
+
+	@Override
+	protected void meetNode(QueryModelNode node) throws X {
+		// resume previous visitor
+		node.visit(visitor);
+	}
+}