mapreduce/src/java/org/apache/hadoop/mapreduce/lib/join/MultiFilterRecordReader.java

/**
 * 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.hadoop.mapreduce.lib.join;

import java.io.IOException;
import java.util.PriorityQueue;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableComparator;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.util.ReflectionUtils;

/**
 * Base class for Composite join returning values derived from multiple
 * sources, but generally not tuples.
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class MultiFilterRecordReader<K extends WritableComparable<?>,
                                              V extends Writable>
    extends CompositeRecordReader<K,V,V> {

  private TupleWritable ivalue = null;

  public MultiFilterRecordReader(int id, Configuration conf, int capacity,
      Class<? extends WritableComparator> cmpcl) throws IOException {
    super(id, capacity, cmpcl);
    setConf(conf);
  }

  /**
   * For each tuple emitted, return a value (typically one of the values
   * in the tuple).
   * Modifying the Writables in the tuple is permitted and unlikely to affect
   * join behavior in most cases, but it is not recommended. It's safer to
   * clone first.
   */
  protected abstract V emit(TupleWritable dst) throws IOException;

  /**
   * Default implementation offers {@link #emit} every Tuple from the
   * collector (the outer join of child RRs).
   */
  protected boolean combine(Object[] srcs, TupleWritable dst) {
    return true;
  }

  /** {@inheritDoc} */
  public boolean nextKeyValue() throws IOException, InterruptedException {
    if (key == null) {
      key = createKey();
    }
    if (value == null) {
      value = createValue();
    }
    if (jc.flush(ivalue)) {
      ReflectionUtils.copy(conf, jc.key(), key);
      ReflectionUtils.copy(conf, emit(ivalue), value);
      return true;
    }
    if (ivalue == null) {
      ivalue = createTupleWritable();
    }
    jc.clear();
    final PriorityQueue<ComposableRecordReader<K,?>> q = 
            getRecordReaderQueue();
    K iterkey = createKey();
    while (q != null && !q.isEmpty()) {
      fillJoinCollector(iterkey);
      jc.reset(iterkey);
      if (jc.flush(ivalue)) {
        ReflectionUtils.copy(conf, jc.key(), key);
        ReflectionUtils.copy(conf, emit(ivalue), value);
        return true;
      }
      jc.clear();
    }
    return false;
  }

  @SuppressWarnings("unchecked")
  public void initialize(InputSplit split, TaskAttemptContext context) 
      throws IOException, InterruptedException {
    super.initialize(split, context);
  }

  /**
   * Return an iterator returning a single value from the tuple.
   * @see MultiFilterDelegationIterator
   */
  protected ResetableIterator<V> getDelegate() {
    return new MultiFilterDelegationIterator();
  }

  /**
   * Proxy the JoinCollector, but include callback to emit.
   */
  protected class MultiFilterDelegationIterator
      implements ResetableIterator<V> {

    public boolean hasNext() {
      return jc.hasNext();
    }

    public boolean next(V val) throws IOException {
      boolean ret;
      if (ret = jc.flush(ivalue)) {
        ReflectionUtils.copy(getConf(), emit(ivalue), val);
      }
      return ret;
    }

    public boolean replay(V val) throws IOException {
      ReflectionUtils.copy(getConf(), emit(ivalue), val);
      return true;
    }

    public void reset() {
      jc.reset(jc.key());
    }

    public void add(V item) throws IOException {
      throw new UnsupportedOperationException();
    }

    public void close() throws IOException {
      jc.close();
    }

    public void clear() {
      jc.clear();
    }
  }

}