[GitHub] apex-malhar pull request #309: [APEXMALHAR-2106][WIP] Support multiple strea...

[bhupeshchawda <gi...@git.apache.org>]

Github user bhupeshchawda commented on a diff in the pull request:

    https://github.com/apache/apex-malhar/pull/309#discussion_r66142732
  
    --- Diff: library/src/main/java/com/datatorrent/lib/stream/MultipleStreamMerger.java ---
    @@ -0,0 +1,277 @@
    +/**
    + * 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 com.datatorrent.lib.stream;
    +
    +import java.util.ArrayList;
    +import java.util.Iterator;
    +
    +import org.apache.hadoop.conf.Configuration;
    +
    +import com.datatorrent.api.DAG;
    +import com.datatorrent.api.DefaultInputPort;
    +import com.datatorrent.api.DefaultOutputPort;
    +import com.datatorrent.api.Module;
    +
    +/**
    + * Module that adds functionality to bypass the platform limitations of combining more than two streams at a time with
    + * Stream Merger.
    + *
    + * Usage:
    + *
    + * dag.addOperator("Stream_1", op1);
    + * dag.addOperator("Stream_2", op2);
    + * dag.addOperator("Stream_3", op3);
    + *
    + * MultipleStreamMerger merger = new MultipleStreamMerger();
    + * merger.merge(op1.out)
    + * .merge(op2.out)
    + * .merge(op3.out)
    + * .insertInto(dag, conf);
    + *
    + * dag.addModule("Merger", merger);
    + *
    + * @param <K>
    + */
    +public class MultipleStreamMerger<K> implements Module
    +{
    +  public class Stream
    +  {
    +    DefaultInputPort destPort;
    +    DefaultOutputPort sourcePort;
    +    String name;
    +
    +    public Stream(String name, DefaultOutputPort sourcePort, DefaultInputPort destPort)
    +    {
    +      this.destPort = destPort;
    +      this.sourcePort = sourcePort;
    +      this.name = name;
    +    }
    +  }
    +
    +  public class NamedMerger
    +  {
    +    StreamMerger<K> merger;
    +    String name;
    +
    +    public NamedMerger(String name, StreamMerger<K> merger)
    +    {
    +      this.merger = merger;
    +      this.name = name;
    +    }
    +  }
    +
    +  private int streamCount = 0;
    +
    +  ArrayList<DefaultOutputPort<K>> streamsToMerge = new ArrayList<>();
    +
    +  public transient ProxyOutputPort<K> streamOutput = new ProxyOutputPort<>();
    +
    +  /**
    +   * Used to define all the sources to be merged into a single stream.
    +   *
    +   * @param sourcePort - The output port from the upstream operator that provides data
    +   * @return The updated MultipleStreamMerger object that tracks which streams should be unified.
    +   */
    +  public MultipleStreamMerger<K> merge(DefaultOutputPort<K> sourcePort)
    +  {
    +    streamsToMerge.add(sourcePort);
    +    return this;
    +  }
    +
    +  /**
    +   * To merge more than two streams at a time, we construct a binary tree of thread-local StreamMerger operators
    +   * E.g.
    +   *
    +   * Tier 0          Tier 1              Tier 2
    +   *
    +   * Stream 1 ->
    +   * StreamMerger_1 ->
    +   * Stream 2 ->
    +   * StreamMerger_Final -> Out
    +   * Stream 3 ->
    +   * StreamMerger_2 ->
    +   * Stream 4 ->
    +   *
    +   * This function updates the provided DAG with the relevant streams.
    +   */
    +  public void mergeStreams(DAG dag, Configuration conf)
    +  {
    +    if (streamsToMerge.size() < 2) {
    +      throw new IllegalArgumentException("Not enough streams to merge, at least two streams must be selected for " +
    +          "merging with `.merge()`.");
    +    }
    +
    +    ArrayList<Stream> streamsToAddToDag = new ArrayList<>();
    +    ArrayList<NamedMerger> operatorsToAdd = new ArrayList<>();
    +
    +    // Determine operators and streams to add to the DAG
    +    constructMergeTree(streamsToAddToDag, operatorsToAdd);
    +
    +    for (NamedMerger m : operatorsToAdd) {
    +      dag.addOperator(m.name, m.merger);
    +    }
    +
    +    for (Stream s : streamsToAddToDag) {
    +      dag.addStream(s.name, s.sourcePort, s.destPort).setLocality(DAG.Locality.CONTAINER_LOCAL);
    +    }
    +  }
    +
    +  /**
    +   * Given a set of streams to be merged (defined via {@link #merge(DefaultOutputPort)}), compute the optimal
    +   * structure of cascading mergers that need to be instantiated, added to the dag, and linked together.
    +   * @param streamsToAddToDag - (output)  A list that is populated with streams that should be added to the  DAG
    +   * @param operatorsToAdd - (output) A list that is populated with operators to be added to the DAG
    +   */
    +  public void constructMergeTree(
    +      ArrayList<Stream> streamsToAddToDag,
    +      ArrayList<NamedMerger> operatorsToAdd)
    +  {
    +    if (streamsToMerge.size() < 2) {
    +      throw new IllegalArgumentException("Not enough streams to merge. Ensure `.merge` was called for each stream " +
    +          "to be added.");
    +    }
    +
    +    // Define the final merger in the sequence and connect its output to the module's output
    +    StreamMerger<K> finalMerger = new StreamMerger<>();
    +    operatorsToAdd.add(new NamedMerger("Merger_Final", finalMerger));
    +    streamOutput.set(finalMerger.out);
    +
    +    ArrayList<ArrayList<StreamMerger<K>>> mergers = new ArrayList<>();
    +
    +    /**
    +     * First, calculate the number of tiers we need to merge all streams given that each merger can only merge two
    +     * streams at a time.
    +     */
    +    int numTiers = (int)Math.ceil(Math.log(streamsToMerge.size()) / Math.log(2));
    +
    +    // Handle the simple case where we only have a single tier (only two streams to merge)
    +    if (numTiers == 1) {
    +      assert (streamsToMerge.size() == 2);
    +      streamsToAddToDag.add(new Stream("FinalMerge_Stream_0", streamsToMerge.get(0), finalMerger.data1));
    +      streamsToAddToDag.add(new Stream("FinalMerge_Stream_1", streamsToMerge.get(1), finalMerger.data2));
    +
    +      // We don't need to add any operators since we've already added the final merger
    +    } else {
    +      Iterator<DefaultOutputPort<K>> streams = streamsToMerge.iterator();
    +
    +      // When assigning streams, we will switch between ports 1 and 2 as we use successive mergers.
    +      boolean usePort1;
    +
    +      // For each tier, create the mergers in that tier, and connect the relevant streams
    +      for (int i = 0; i < numTiers - 1; i++) {
    +        int streamIdx = 0;
    +        usePort1 = true;
    +
    +        int numMergers = (int)Math.ceil(streamsToMerge.size() / Math.pow(2, i + 1));
    --- End diff --
    
    Should this be floor instead of ceil? The one odd stream can be directly fed to the final tier.


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