    001/*
    002 * Copyright (c) 2007-2016 Concurrent, Inc. All Rights Reserved.
    003 *
    004 * Project and contact information: http://www.cascading.org/
    005 *
    006 * This file is part of the Cascading project.
    007 *
    008 * Licensed under the Apache License, Version 2.0 (the "License");
    009 * you may not use this file except in compliance with the License.
    010 * You may obtain a copy of the License at
    011 *
    012 *     http://www.apache.org/licenses/LICENSE-2.0
    013 *
    014 * Unless required by applicable law or agreed to in writing, software
    015 * distributed under the License is distributed on an "AS IS" BASIS,
    016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    017 * See the License for the specific language governing permissions and
    018 * limitations under the License.
    019 */
    020
    021package cascading.operation.filter;
    022
    023import java.beans.ConstructorProperties;
    024
    025import cascading.flow.FlowProcess;
    026import cascading.management.annotation.Property;
    027import cascading.management.annotation.PropertyDescription;
    028import cascading.management.annotation.Visibility;
    029import cascading.operation.BaseOperation;
    030import cascading.operation.Filter;
    031import cascading.operation.FilterCall;
    032import cascading.operation.OperationCall;
    033
    034/**
    035 * Class Limit is a {@link Filter} that will limit the number of {@link cascading.tuple.Tuple} instances that it will
    036 * allow to pass.
    037 * <br/>
    038 * Note that the limit value is roughly a suggestion. It attempts to divide the limit number by the number of concurrent
    039 * tasks, but knowing the number of tasks isn't easily available from configuration information provided to individual
    040 * tasks. Further, the number of records/lines available to a task may be less than the limit amount.
    041 * <br/>
    042 * More consistent results will be received from using {@link Sample}.
    043 *
    044 * @see Sample
    045 */
    046public class Limit extends BaseOperation<Limit.Context> implements Filter<Limit.Context>
    047  {
    048  private long limit = 0;
    049
    050  public static class Context
    051    {
    052    public long limit = 0;
    053    public long count = 0;
    054
    055    public boolean increment()
    056      {
    057      if( limit == count )
    058        return true;
    059
    060      count++;
    061
    062      return false;
    063      }
    064    }
    065
    066  /**
    067   * Creates a new Limit class that only allows limit number of Tuple instances to pass.
    068   *
    069   * @param limit the number of tuples to let pass
    070   */
    071  @ConstructorProperties({"limit"})
    072  public Limit( long limit )
    073    {
    074    this.limit = limit;
    075    }
    076
    077  @Property(name = "limit", visibility = Visibility.PUBLIC)
    078  @PropertyDescription("The upper limit.")
    079  public long getLimit()
    080    {
    081    return limit;
    082    }
    083
    084  @Override
    085  public void prepare( FlowProcess flowProcess, OperationCall<Context> operationCall )
    086    {
    087    super.prepare( flowProcess, operationCall );
    088
    089    Context context = new Context();
    090
    091    operationCall.setContext( context );
    092
    093    int numTasks = flowProcess.getNumProcessSlices();
    094    int taskNum = flowProcess.getCurrentSliceNum();
    095
    096    context.limit = (long) Math.floor( (double) limit / (double) numTasks );
    097
    098    long remainingLimit = limit % numTasks;
    099
    100    // evenly divide limits across tasks
    101    context.limit += taskNum < remainingLimit ? 1 : 0;
    102    }
    103
    104  @Override
    105  public boolean isRemove( FlowProcess flowProcess, FilterCall<Context> filterCall )
    106    {
    107    return filterCall.getContext().increment();
    108    }
    109
    110  @Override
    111  public boolean equals( Object object )
    112    {
    113    if( this == object )
    114      return true;
    115    if( !( object instanceof Limit ) )
    116      return false;
    117    if( !super.equals( object ) )
    118      return false;
    119
    120    Limit limit1 = (Limit) object;
    121
    122    if( limit != limit1.limit )
    123      return false;
    124
    125    return true;
    126    }
    127
    128  @Override
    129  public int hashCode()
    130    {
    131    int result = super.hashCode();
    132    result = 31 * result + (int) ( limit ^ limit >>> 32 );
    133    return result;
    134    }
    135  }