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ARQ is a SPARQL 1.1 query engine for Apache Jena
/**
* 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.apache.jena.atlas.data;
import java.io.File ;
import java.io.FileNotFoundException ;
import java.util.ArrayList ;
import java.util.Comparator ;
import java.util.Iterator ;
import java.util.List ;
import java.util.NoSuchElementException ;
import org.apache.jena.atlas.AtlasException ;
import org.apache.jena.atlas.iterator.Iter ;
import org.apache.jena.atlas.lib.Closeable ;
import org.apache.jena.atlas.lib.FileOps ;
/**
* This class is like {@link DistinctDataBag} except that you are informed if the item you just
* added was known to be distinct. This will normally only work until the first spill. After that,
* the system may not be able to tell for sure, and will thus return false. When you are finished
* adding items, you may call {@link #netIterator()} to get any distinct items that are in the
* spill files but were not indicated as distinct previously.
*/
public class DistinctDataNet extends DistinctDataBag
{
protected File firstSpillFile;
public DistinctDataNet(ThresholdPolicy policy, SerializationFactory serializerFactory, Comparator comparator)
{
super(policy, serializerFactory, comparator) ;
}
/**
* @return true if the item added is known to be distinct.
*/
public boolean netAdd(E item)
{
long s = size ;
super.add(item) ;
return !spilled && size > s ;
}
@Override
protected void registerSpillFile(File spillFile)
{
// If this is the first time spilling, then keep this spill file separate
if (!spilled)
{
firstSpillFile = spillFile;
}
else
{
super.registerSpillFile(spillFile);
}
}
@Override
protected void deleteSpillFiles()
{
super.deleteSpillFiles();
if (null != firstSpillFile)
{
FileOps.delete(firstSpillFile, false);
firstSpillFile = null;
}
}
// Used by the .iterator() method
@Override
protected List getSpillFiles()
{
List toReturn = new ArrayList<>(super.getSpillFiles());
if (null != firstSpillFile)
{
toReturn.add(firstSpillFile);
}
return toReturn;
}
// TODO: Will be used by the .netIterator() method
protected List getNetSpillFiles()
{
return super.getSpillFiles();
}
/**
* Returns an iterator to all additional items that are distinct but were
* not reported to be so at the time {@link #netAdd(Object)} was invoked.
*
* If you do not exhaust the iterator, you should call {@link org.apache.jena.atlas.iterator.Iter#close(Iterator)}
* to be sure any open file handles are closed.
*/
public Iterator netIterator()
{
// If we havn't spilled, then we have already indicated all distinct values via .netAdd()
if (!spilled)
{
return Iter.nullIterator();
}
Iterator blacklist;
try
{
blacklist = getInputIterator(firstSpillFile);
}
catch ( FileNotFoundException e )
{
throw new AtlasException("Cannot find the first spill file", e);
}
// TODO: Improve performance by making the superclass .iterator() use getNetSpillFiles()
// instead of getSpillFiles() so it doesn't contain the contents of the first file
Iterator rest = super.iterator();
SortedDiffIterator sdi = SortedDiffIterator.create(rest, blacklist, comparator);
registerCloseableIterator(sdi);
return sdi;
}
/**
* Produces the set difference of two sorted set sequences.
*/
protected static class SortedDiffIterator implements Iterator, Closeable
{
private final Iterator grayList;
private final Iterator blackList;
private final Comparator comp;
private boolean finished = false;
private boolean blackSlotFull = false;
private T white;
private T black;
/**
* Produces the set difference of two sorted set sequences using the natural ordering of the items
* (null items will always be considered less than any other items).
*
* @param first An Iterator<T> whose elements that are not also in second will be returned.
* @param second An Iterator<T> whose elements that also occur in the first sequence will cause those elements to be removed from the returned sequence.
*/
public static > SortedDiffIterator create(Iterator first, Iterator second)
{
return create(first, second, new Comparator()
{
@Override
public int compare(S o1, S o2)
{
if (null == o1 && null == o2) return 0;
if (null == o1) return -1;
if (null == o2) return 1;
return o1.compareTo(o2);
}
});
}
/**
* Produces the set difference of two sorted set sequences using the specified comparator.
*
* @param first An Iterator<T> whose elements that are not also in second will be returned.
* @param second An Iterator<T> whose elements that also occur in the first sequence will cause those elements to be removed from the returned sequence.
* @param comparator The comparator used to compare the elements from each iterator.
*/
public static SortedDiffIterator create(Iterator first, Iterator second, Comparator comparator)
{
return new SortedDiffIterator<>(first, second, comparator);
}
private SortedDiffIterator(Iterator first, Iterator second, Comparator comparator)
{
this.grayList = first;
this.blackList = second;
this.comp = comparator;
// Prime the white item
fill();
}
private void fill()
{
if (finished) return;
if (!grayList.hasNext())
{
close();
return;
}
if (!blackSlotFull)
{
if (!blackList.hasNext())
{
white = grayList.next();
return;
}
black = blackList.next();
blackSlotFull = true;
}
// Outer loop advances white
while (true)
{
if (!grayList.hasNext())
{
close();
return;
}
white = grayList.next();
int cmp = comp.compare(white, black);
if (cmp < 0) return;
// Inner loop advances black until white is less than or equal to it
while (cmp > 0)
{
if (!blackList.hasNext())
{
black = null;
blackSlotFull = false;
return;
}
black = blackList.next();
cmp = comp.compare(white, black);
if (cmp < 0) return;
}
}
}
@Override
public boolean hasNext()
{
return !finished;
}
@Override
public T next()
{
if (finished) throw new NoSuchElementException();
T toReturn = white;
fill();
return toReturn;
}
@Override
public void remove()
{
throw new UnsupportedOperationException("SortedDiffIterator.remove");
}
@Override
public void close()
{
finished = true;
white = null;
black = null;
Iter.close(grayList);
Iter.close(blackList);
}
}
}