/**
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.rdf.internal.IV;
import com.bigdata.rdf.internal.constraints.INeedsMaterialization;
import com.bigdata.rdf.internal.constraints.IPassesMaterialization;
import com.bigdata.rdf.internal.constraints.INeedsMaterialization.Requirement;
/**
* Operator reports an arbitrary value from presented binding sets for the given
* variable. Missing values are not chosen when non-missing values are
* available.
*
* @author thompsonbry
*/
public class SAMPLE extends AggregateBase<IV> implements IPassesMaterialization{
/**
*
*/
private static final long serialVersionUID = 1L;
public SAMPLE(SAMPLE op) {
super(op);
}
public SAMPLE(BOp[] args, Map<String, Object> annotations) {
super(args, annotations);
}
public SAMPLE(boolean distinct, IValueExpression<IV> expr) {
super(/*FunctionCode.SAMPLE,*/ distinct, expr);
}
/**
* The sampled value and initially <code>null</code>.
* <p>
* Note: This field is guarded by the monitor on the {@link SAMPLE}
* instance.
*/
private transient IV sample = 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) {
final IValueExpression<IV<?, ?>> expr = (IValueExpression<IV<?, ?>>) get(0);
final IV<?, ?> iv = expr.get(bindingSet);
if (iv != null && sample == null) {
// Take the first non-null observed value.
sample = iv;
}
return sample;
}
synchronized public void reset() {
sample = null;
firstCause = null;
}
synchronized public IV done() {
if (firstCause != null) {
throw new RuntimeException(firstCause);
}
return sample;
}
/**
* We can take a sample without materializing anything.
*/
public Requirement getRequirement() {
return INeedsMaterialization.Requirement.NEVER;
}
}