/*
* 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.giraph.edge;
import it.unimi.dsi.fastutil.longs.LongArrayList;
import it.unimi.dsi.fastutil.longs.LongIterator;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.Collection;
import java.util.Iterator;
/**
* Implementation of {@link OutEdges} with long ids and null edge
* values, backed by a dynamic primitive array.
* Parallel edges are allowed.
* Note: this implementation is optimized for space usage,
* but random access and edge removals are expensive.
*/
public class LongNullArrayEdges
implements ReuseObjectsOutEdges<LongWritable, NullWritable>,
MutableOutEdges<LongWritable, NullWritable> {
/** Array of target vertex ids. */
private LongArrayList neighbors;
@Override
public void initialize(Iterable<Edge<LongWritable, NullWritable>> edges) {
// If the iterable is actually a collection, we can cheaply get the
// size and initialize the arrays with the expected capacity.
if (edges instanceof Collection) {
int numEdges =
((Collection<Edge<LongWritable, NullWritable>>) edges).size();
initialize(numEdges);
} else {
initialize();
}
for (Edge<LongWritable, NullWritable> edge : edges) {
add(edge);
}
}
@Override
public void initialize(int capacity) {
neighbors = new LongArrayList(capacity);
}
@Override
public void initialize() {
neighbors = new LongArrayList();
}
@Override
public void add(Edge<LongWritable, NullWritable> edge) {
neighbors.add(edge.getTargetVertexId().get());
}
/**
* If the backing array is more than four times as big as the number of
* elements, halve its size.
*/
private void trim() {
if (neighbors.elements().length > 4 * neighbors.size()) {
neighbors.trim(neighbors.elements().length / 2);
}
}
/**
* Remove edge at position i.
*
* @param i Position of edge to be removed
*/
private void removeAt(int i) {
// The order of the edges is irrelevant, so we can simply replace
// the deleted edge with the rightmost element, thus achieving constant
// time.
if (i == neighbors.size() - 1) {
neighbors.popLong();
} else {
neighbors.set(i, neighbors.popLong());
}
// If needed after the removal, trim the array.
trim();
}
@Override
public void remove(LongWritable targetVertexId) {
// Thanks to the constant-time implementation of removeAt(int),
// we can remove all matching edges in linear time.
for (int i = neighbors.size() - 1; i >= 0; --i) {
if (neighbors.get(i) == targetVertexId.get()) {
removeAt(i);
}
}
}
@Override
public int size() {
return neighbors.size();
}
@Override
public Iterator<Edge<LongWritable, NullWritable>> iterator() {
// Returns an iterator that reuses objects.
// The downcast is fine because all concrete Edge implementations are
// mutable, but we only expose the mutation functionality when appropriate.
return (Iterator) mutableIterator();
}
@Override
public Iterator<MutableEdge<LongWritable, NullWritable>> mutableIterator() {
return new Iterator<MutableEdge<LongWritable, NullWritable>>() {
/** Current position in the array. */
private int offset = 0;
/** Representative edge object. */
private MutableEdge<LongWritable, NullWritable> representativeEdge =
EdgeFactory.createReusable(new LongWritable());
public boolean hasNext() {
return offset < neighbors.size();
}
@Override
public MutableEdge<LongWritable, NullWritable> next() {
representativeEdge.getTargetVertexId().set(neighbors.get(offset++));
return representativeEdge;
}
@Override
public void remove() {
// Since removeAt() might replace the deleted edge with the last edge
// in the array, we need to decrease the offset so that the latter
// won't be skipped.
removeAt(--offset);
}
};
}
@Override
public void write(DataOutput out) throws IOException {
out.writeInt(neighbors.size());
LongIterator neighborsIt = neighbors.iterator();
while (neighborsIt.hasNext()) {
out.writeLong(neighborsIt.nextLong());
}
}
@Override
public void readFields(DataInput in) throws IOException {
int numEdges = in.readInt();
initialize(numEdges);
for (int i = 0; i < numEdges; ++i) {
neighbors.add(in.readLong());
}
}
}