[GitHub] incubator-apex-malhar pull request: MLHR-1897 #comment added manag...

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

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

    https://github.com/apache/incubator-apex-malhar/pull/145#discussion_r53704929
  
    --- Diff: library/src/main/java/com/datatorrent/lib/state/managed/TimeBucketAssigner.java ---
    @@ -0,0 +1,223 @@
    +/**
    + * 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.state.managed;
    +
    +import java.util.Calendar;
    +import java.util.Set;
    +
    +import javax.validation.constraints.NotNull;
    +
    +import org.joda.time.Duration;
    +
    +import com.esotericsoftware.kryo.serializers.FieldSerializer;
    +import com.esotericsoftware.kryo.serializers.JavaSerializer;
    +import com.google.common.collect.Sets;
    +
    +import com.datatorrent.api.Component;
    +import com.datatorrent.api.Context;
    +import com.datatorrent.lib.appdata.query.WindowBoundedService;
    +
    +/**
    + * Keeps track of time buckets.<br/>
    + *
    + * The data of a bucket is further divided into time-buckets. This component controls the length of time buckets,
    + * which time-bucket an event falls into and sliding the time boundaries.
    + * <p/>
    + *
    + * The configuration {@link #expireBefore} and {@link #bucketSpan}  are used to calculate number of time-buckets.
    + * For eg. if <code>expireBefore = 1 hour</code> and <code>bucketSpan = 30 minutes</code>, then <code>
    + *   numBuckets = 60 minutes/ 30 minutes = 2 </code>.
    + * <p/>
    + *
    + * The time boundaries- start and end, periodically move by span of a single time-bucket. Any event with time < start
    + * is expired. These boundaries slide between application window by another thread and not the operator thread.
    + */
    +public class TimeBucketAssigner implements Component<Context.OperatorContext>
    +{
    +  @NotNull
    +  @FieldSerializer.Bind(JavaSerializer.class)
    +  private Duration expireBefore = Duration.standardDays(2);
    +
    +  @FieldSerializer.Bind(JavaSerializer.class)
    +  private Duration bucketSpan;
    +
    +  private long bucketSpanMillis;
    +
    +  private long fixedStartTime;
    +  private long startTime;
    +  private long endTime;
    +  private int numBuckets;
    +
    +  private boolean initialized;
    +
    +  private transient WindowBoundedService windowBoundedService;
    +
    +  @NotNull
    +  private final transient Set<Listener> listeners = Sets.newHashSet();
    --- End diff --
    
    From @amberarrow 
    Do we need a set here, i.e. do we expect more than one listener ? With a set, several questions come up:
    1. We should document the fact that the listener should ensure that set membership works correctly by implementing hashCode()/equals().
    2. The purgeTimeBucketsBefore() method should not take a long time since it is run with a lock held in the expiry task.
    3. Do we need an unregister() method to remove a listener ?
    
    All these go away if we limit it to just 1 listener.
    ---------------
     
    Made the change


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