src/org/apache/pig/data/ReadOnceBag.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.pig.data;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.Iterator;

import org.apache.pig.PigException;
import org.apache.pig.backend.executionengine.ExecException;
import org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.Packager;
import org.apache.pig.impl.io.NullableTuple;
import org.apache.pig.impl.io.PigNullableWritable;

/**
 * This bag does not store the tuples in memory, but has access to an iterator
 * typically provided by Hadoop. Use this when you already have an iterator over
 * tuples and do not want to copy over again to a new bag.
 */
public class ReadOnceBag implements DataBag {

    // The Packager that created this
    protected Packager pkgr;

    //The iterator of Tuples. Marked transient because we will never serialize this.
    protected transient Iterator<NullableTuple> tupIter;

    // The key being worked on
    protected PigNullableWritable keyWritable;

    /**
     *
     */
    private static final long serialVersionUID = 2L;

    public ReadOnceBag() {
    }

    /**
     * This constructor creates a bag out of an existing iterator
     * of tuples by taking ownership of the iterator and NOT
     * copying the elements of the iterator.
     * @param pkg POPackageLite
     * @param tupIter Iterator<NullableTuple>
     * @param key Object
     */
    public ReadOnceBag(Packager pkgr, Iterator<NullableTuple> tupIter,
            PigNullableWritable keyWritable) {
        this.pkgr = pkgr;
        this.tupIter = tupIter;
        this.keyWritable = keyWritable;
    }

    /* (non-Javadoc)
     * @see org.apache.pig.impl.util.Spillable#getMemorySize()
     */
    @Override
    public long getMemorySize() {
        return 0;
    }

    /* (non-Javadoc)
     * @see org.apache.pig.impl.util.Spillable#spill()

     */
    @Override
    public long spill() {
        throw new RuntimeException("ReadOnceBag does not support spill operation");
    }

    /* (non-Javadoc)
     * @see org.apache.pig.data.DataBag#add(org.apache.pig.data.Tuple)
     */
    @Override
    public void add(Tuple t) {
        throw new RuntimeException("ReadOnceBag does not support add operation");
    }

    /* (non-Javadoc)
     * @see org.apache.pig.data.DataBag#addAll(org.apache.pig.data.DataBag)
     */
    @Override
    public void addAll(DataBag b) {
        throw new RuntimeException("ReadOnceBag does not support addAll operation");
    }

    /* (non-Javadoc)
     * @see org.apache.pig.data.DataBag#clear()
     */
    @Override
    public void clear() {
        throw new RuntimeException("ReadOnceBag does not support clear operation");
    }

    /* (non-Javadoc)
     * @see org.apache.pig.data.DataBag#isDistinct()
     */
    @Override
    public boolean isDistinct() {
        throw new RuntimeException("ReadOnceBag does not support isDistinct operation");
    }

    /* (non-Javadoc)
     * @see org.apache.pig.data.DataBag#isSorted()
     */
    @Override
    public boolean isSorted() {
        throw new RuntimeException("ReadOnceBag does not support isSorted operation");
    }

    /* (non-Javadoc)
     * @see org.apache.pig.data.DataBag#iterator()
     */
    @Override
    public Iterator<Tuple> iterator() {
        return new ReadOnceBagIterator();
    }

    /* (non-Javadoc)
     * @see org.apache.pig.data.DataBag#markStale(boolean)
     */
    @Override
    public void markStale(boolean stale) {
        throw new RuntimeException("ReadOnceBag does not support markStale operation");
    }

    /* (non-Javadoc)
     * @see org.apache.pig.data.DataBag#size()
     */
    @Override
    public long size() {
        throw new RuntimeException("ReadOnceBag does not support size operation");
    }

    /* (non-Javadoc)
     * @see org.apache.hadoop.io.Writable#readFields(java.io.DataInput)
     */
    @Override
    public void readFields(DataInput in) throws IOException {
        throw new RuntimeException("ReadOnceBag does not support readFields operation");
    }

    /* (non-Javadoc)
     * @see org.apache.hadoop.io.Writable#write(java.io.DataOutput)
     */
    @Override
    public void write(DataOutput out) throws IOException {
        int errCode = 2142;
        String msg = "ReadOnceBag should never be serialized.";
        throw new ExecException(msg, errCode, PigException.BUG);
    }

    /* (non-Javadoc)
     * @see java.lang.Comparable#compareTo(java.lang.Object)
     * This has to be defined since DataBag implements
     * Comparable although, in this case we cannot really compare.
     */
    @Override
    public int compareTo(Object o) {
        throw new RuntimeException("ReadOnceBags cannot be compared");
    }

    @Override
    public boolean equals(Object other) {
        if (other instanceof ReadOnceBag) {
            if (pkgr.getKeyTuple()) {
                if (tupIter == ((ReadOnceBag) other).tupIter
                        && pkgr.getKeyTuple() == ((ReadOnceBag) other).pkgr
                                .getKeyTuple()
                        && pkgr.getKeyAsTuple().equals(
                                ((ReadOnceBag) other).pkgr.getKeyAsTuple())) {
                    return true;
                } else {
                    return false;
                }
            } else {
                if (tupIter == ((ReadOnceBag) other).tupIter
                        && pkgr.getKey().equals(
                                ((ReadOnceBag) other).pkgr.getKey())) {
                    return true;
                } else {
                    return false;
                }
            }
        }
        return false;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        if (pkgr.getKeyTuple())
        {
            hash = hash * 31 + pkgr.getKeyAsTuple().hashCode();
        }
        else
        {
            hash = hash * 31 + pkgr.getKey().hashCode();
        }
        return hash;
    }

    protected class ReadOnceBagIterator implements Iterator<Tuple>
    {
        /* (non-Javadoc)
         * @see java.util.Iterator#hasNext()
         */
        @Override
        public boolean hasNext() {
            return tupIter.hasNext();
        }

        /* (non-Javadoc)
         * @see java.util.Iterator#next()
         */
        @Override
        public Tuple next() {
            NullableTuple ntup = tupIter.next();
            int index = ntup.getIndex();
            Tuple ret = null;
            try {
                ret = pkgr.getValueTuple(keyWritable, ntup, index);
            } catch (ExecException e)
            {
                throw new RuntimeException("ReadOnceBag failed to get value tuple : "+e.toString());
            }
            return ret;
        }

        /* (non-Javadoc)
         * @see java.util.Iterator#remove()
         */
        @Override
        public void remove() {
            throw new RuntimeException("ReadOnceBag.iterator().remove() is not allowed");
        }
    }
}