/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package com.bigdata.bop.rdf.aggregate;
import java.util.Map;
import com.bigdata.bop.BOp;
import com.bigdata.bop.IBindingSet;
import com.bigdata.bop.IValueExpression;
import com.bigdata.bop.aggregate.AggregateBase;
import com.bigdata.bop.solutions.IVComparator;
import com.bigdata.rdf.internal.IV;
import com.bigdata.rdf.internal.constraints.CompareBOp;
import com.bigdata.rdf.internal.constraints.INeedsMaterialization;
/**
* Operator reports the minimum observed value over the presented binding sets
* for the given variable using SPARQL ORDER_BY semantics. Missing values are
* ignored.
* <p>
* Note: MIN (and MAX) are defined in terms of the ORDER_BY semantics for
* SPARQL. Therefore, this must handle comparisons when the value is not an IV,
* e.g., using {@link IVComparator}.
*
* @author thompsonbry
*
* TODO What is reported if there are no non-null observations?
*/
public class MAX extends AggregateBase<IV> implements INeedsMaterialization{
// private static final transient Logger log = Logger.getLogger(MAX.class);
/**
*
*/
private static final long serialVersionUID = 1L;
/**
* Provides SPARQL <em>ORDER BY</em> semantics.
*
* @see <a href="https://sourceforge.net/apps/trac/bigdata/ticket/736">
* MIN() malfunction </a>
*/
private static final transient IVComparator comparator = new IVComparator();
public MAX(final MAX op) {
super(op);
}
public MAX(final BOp[] args, final Map<String, Object> annotations) {
super(args, annotations);
}
public MAX(final boolean distinct, final IValueExpression...expr) {
super(distinct, expr);
}
/**
* The maximum observed value and initially <code>null</code>.
* <p>
* Note: This field is guarded by the monitor on the {@link MAX} instance.
*/
private transient IV max = null;
/**
* The first error encountered since the last {@link #reset()}.
*/
private transient Throwable firstCause = null;
synchronized public IV get(final IBindingSet bindingSet) {
try {
return doGet(bindingSet);
} catch (Throwable t) {
if (firstCause == null) {
firstCause = t;
}
throw new RuntimeException(t);
}
}
private IV doGet(final IBindingSet bindingSet) {
for (int i = 0; i < arity(); i++) {
final IValueExpression<IV<?, ?>> expr = (IValueExpression<IV<?, ?>>) get(i);
final IV iv = expr.get(bindingSet);
if (iv != null) {
/*
* Aggregate non-null values.
*/
if (max == null) {
max = iv;
} else {
// Note: This is SPARQL GT semantics, not ORDER BY.
// if (CompareBOp.compare(iv, max, CompareOp.GT)) {
// SPARQL ORDER_BY semantics
if (comparator.compare(iv, max) > 0) {
max = iv;
}
}
}
}
return max;
}
@Override
synchronized public void reset() {
max = null;
firstCause = null;
}
synchronized public IV done() {
if (firstCause != null) {
throw new RuntimeException(firstCause);
}
return max;
}
/**
* Note: {@link MAX} only works on pretty much anything and uses the same
* semantics as {@link CompareBOp} (it is essentially the transitive closure
* of LT over the column projection of the inner expression). This probably
* means that we always need to materialize something unless it is an inline
* numeric IV.
*
* FIXME MikeP: What is the right return value here?
*/
@Override
public Requirement getRequirement() {
return INeedsMaterialization.Requirement.ALWAYS;
}
}