001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    
019    package org.apache.hadoop.mapred.join;
020    
021    import java.io.IOException;
022    import java.util.PriorityQueue;
023    
024    import org.apache.hadoop.classification.InterfaceAudience;
025    import org.apache.hadoop.classification.InterfaceStability;
026    import org.apache.hadoop.io.Writable;
027    import org.apache.hadoop.io.WritableComparable;
028    import org.apache.hadoop.io.WritableComparator;
029    import org.apache.hadoop.io.WritableUtils;
030    import org.apache.hadoop.mapred.JobConf;
031    
032    /**
033     * Base class for Composite joins returning Tuples of arbitrary Writables.
034     */
035    @InterfaceAudience.Public
036    @InterfaceStability.Stable
037    public abstract class JoinRecordReader<K extends WritableComparable>
038        extends CompositeRecordReader<K,Writable,TupleWritable>
039        implements ComposableRecordReader<K,TupleWritable> {
040    
041      public JoinRecordReader(int id, JobConf conf, int capacity,
042          Class<? extends WritableComparator> cmpcl) throws IOException {
043        super(id, capacity, cmpcl);
044        setConf(conf);
045      }
046    
047      /**
048       * Emit the next set of key, value pairs as defined by the child
049       * RecordReaders and operation associated with this composite RR.
050       */
051      public boolean next(K key, TupleWritable value) throws IOException {
052        if (jc.flush(value)) {
053          WritableUtils.cloneInto(key, jc.key());
054          return true;
055        }
056        jc.clear();
057        K iterkey = createKey();
058        final PriorityQueue<ComposableRecordReader<K,?>> q = getRecordReaderQueue();
059        while (!q.isEmpty()) {
060          fillJoinCollector(iterkey);
061          jc.reset(iterkey);
062          if (jc.flush(value)) {
063            WritableUtils.cloneInto(key, jc.key());
064            return true;
065          }
066          jc.clear();
067        }
068        return false;
069      }
070    
071      /** {@inheritDoc} */
072      public TupleWritable createValue() {
073        return createInternalValue();
074      }
075    
076      /**
077       * Return an iterator wrapping the JoinCollector.
078       */
079      protected ResetableIterator<TupleWritable> getDelegate() {
080        return new JoinDelegationIterator();
081      }
082    
083      /**
084       * Since the JoinCollector is effecting our operation, we need only
085       * provide an iterator proxy wrapping its operation.
086       */
087      protected class JoinDelegationIterator
088          implements ResetableIterator<TupleWritable> {
089    
090        public boolean hasNext() {
091          return jc.hasNext();
092        }
093    
094        public boolean next(TupleWritable val) throws IOException {
095          return jc.flush(val);
096        }
097    
098        public boolean replay(TupleWritable val) throws IOException {
099          return jc.replay(val);
100        }
101    
102        public void reset() {
103          jc.reset(jc.key());
104        }
105    
106        public void add(TupleWritable item) throws IOException {
107          throw new UnsupportedOperationException();
108        }
109    
110        public void close() throws IOException {
111          jc.close();
112        }
113    
114        public void clear() {
115          jc.clear();
116        }
117      }
118    }