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From vrozov <...@git.apache.org>
Subject [GitHub] apex-malhar pull request #319: APEXMALHAR-2085: REVIEW ONLY: Operator suppor...
Date Tue, 05 Jul 2016 17:56:07 GMT
Github user vrozov commented on a diff in the pull request:

    https://github.com/apache/apex-malhar/pull/319#discussion_r69608324
  
    --- Diff: library/src/main/java/org/apache/apex/malhar/lib/window/Accumulation.java ---
    @@ -0,0 +1,76 @@
    +/**
    + * 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.apex.malhar.lib.window;
    +
    +import org.apache.hadoop.classification.InterfaceStability;
    +
    +/**
    + * This interface is for the processing part of the WindowedOperator.
    + * We can assume that all stateful processing of the WindowedOperator is a form of accumulation.
    + *
    + * In most cases, AccumT is the same as OutputT. But in some cases, the accumulated type
and the output type may be
    + * different. For example, if we are doing the AVERAGE of doubles, InputT will be double,
and we need the SUM and the
    + * COUNT stored as type AccumT, and AccumT will be a pair of double and long, in which
double is the sum of the inputs,
    + * and long is the number of inputs. OutputT will be double, because it represents the
average of the inputs.
    + */
    +@InterfaceStability.Evolving
    +public interface Accumulation<InputT, AccumT, OutputT>
    +{
    +  /**
    +   * Returns the default accumulated value when nothing has been accumulated
    +   *
    +   * @return
    +   */
    +  AccumT defaultAccumulatedValue();
    +
    +  /**
    +   * Accumulates the input to the accumulated value
    +   *
    +   * @param accumulatedValue
    +   * @param input
    +   * @return
    +   */
    +  AccumT accumulate(AccumT accumulatedValue, InputT input);
    --- End diff --
    
    What is the reason to make the interface stateless? Should it be stateful? My concern
is with the interface promoting boxing/unboxing pattern and leading to an excessive GC.


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