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Package for Faceted Indexing and Search
package org.apache.lucene.facet.taxonomy.directory;
import java.io.IOException;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermPositions;
import org.apache.lucene.facet.taxonomy.TaxonomyReader;
/**
* 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.
*/
// getParent() needs to be extremely efficient, to the point that we need
// to fetch all the data in advance into memory, and answer these calls
// from memory. Currently we use a large integer array, which is
// initialized when the taxonomy is opened, and potentially enlarged
// when it is refresh()ed.
/**
* @lucene.experimental
*/
class ParentArray {
// These arrays are not syncrhonized. Rather, the reference to the array
// is volatile, and the only writing operation (refreshPrefetchArrays)
// simply creates a new array and replaces the reference. The volatility
// of the reference ensures the correct atomic replacement and its
// visibility properties (the content of the array is visible when the
// new reference is visible).
private volatile int prefetchParentOrdinal[] = null;
public int[] getArray() {
return prefetchParentOrdinal;
}
/**
* refreshPrefetch() refreshes the parent array. Initially, it fills the
* array from the positions of an appropriate posting list. If called during
* a refresh(), when the arrays already exist, only values for new documents
* (those beyond the last one in the array) are read from the positions and
* added to the arrays (that are appropriately enlarged). We assume (and
* this is indeed a correct assumption in our case) that existing categories
* are never modified or deleted.
*/
void refresh(IndexReader indexReader) throws IOException {
// Note that it is not necessary for us to obtain the read lock.
// The reason is that we are only called from refresh() (precluding
// another concurrent writer) or from the constructor (when no method
// could be running).
// The write lock is also not held during the following code, meaning
// that reads *can* happen while this code is running. The "volatile"
// property of the prefetchParentOrdinal and prefetchDepth array
// references ensure the correct visibility property of the assignment
// but other than that, we do *not* guarantee that a reader will not
// use an old version of one of these arrays (or both) while a refresh
// is going on. But we find this acceptable - until a refresh has
// finished, the reader should not expect to see new information
// (and the old information is the same in the old and new versions).
int first;
int num = indexReader.maxDoc();
if (prefetchParentOrdinal==null) {
prefetchParentOrdinal = new int[num];
// Starting Lucene 2.9, following the change LUCENE-1542, we can
// no longer reliably read the parent "-1" (see comment in
// LuceneTaxonomyWriter.SinglePositionTokenStream). We have no way
// to fix this in indexing without breaking backward-compatibility
// with existing indexes, so what we'll do instead is just
// hard-code the parent of ordinal 0 to be -1, and assume (as is
// indeed the case) that no other parent can be -1.
if (num>0) {
prefetchParentOrdinal[0] = TaxonomyReader.INVALID_ORDINAL;
}
first = 1;
} else {
first = prefetchParentOrdinal.length;
if (first==num) {
return; // nothing to do - no category was added
}
// In Java 6, we could just do Arrays.copyOf()...
int[] newarray = new int[num];
System.arraycopy(prefetchParentOrdinal, 0, newarray, 0,
prefetchParentOrdinal.length);
prefetchParentOrdinal = newarray;
}
// Read the new part of the parents array from the positions:
TermPositions positions = indexReader.termPositions(
new Term(Consts.FIELD_PAYLOADS, Consts.PAYLOAD_PARENT));
try {
if (!positions.skipTo(first) && first < num) {
throw new CorruptIndexException("Missing parent data for category " + first);
}
for (int i=first; i= i (this is an
// invariant kept throughout this loop)
if (positions.doc()==i) {
if (positions.freq() == 0) { // shouldn't happen
throw new CorruptIndexException(
"Missing parent data for category "+i);
}
// TODO (Facet): keep a local (non-volatile) copy of the prefetchParentOrdinal
// reference, because access to volatile reference is slower (?).
// Note: The positions we get here are one less than the position
// increment we added originally, so we get here the right numbers:
prefetchParentOrdinal[i] = positions.nextPosition();
if (!positions.next()) {
if ( i+1 < num ) {
throw new CorruptIndexException(
"Missing parent data for category "+(i+1));
}
break;
}
} else { // this shouldn't happen
throw new CorruptIndexException(
"Missing parent data for category "+i);
}
}
} finally {
positions.close(); // to be on the safe side.
}
}
/**
* add() is used in LuceneTaxonomyWriter, not in LuceneTaxonomyReader.
* It is only called from a synchronized method, so it is not reentrant,
* and also doesn't need to worry about reads happening at the same time.
*
* NOTE: add() and refresh() CANNOT be used together. If you call add(),
* this changes the arrays and refresh() can no longer be used.
*/
void add(int ordinal, int parentOrdinal) throws IOException {
if (ordinal >= prefetchParentOrdinal.length) {
// grow the array, if necessary.
// In Java 6, we could just do Arrays.copyOf()...
int[] newarray = new int[ordinal*2+1];
System.arraycopy(prefetchParentOrdinal, 0, newarray, 0,
prefetchParentOrdinal.length);
prefetchParentOrdinal = newarray;
}
prefetchParentOrdinal[ordinal] = parentOrdinal;
}
}