    001    /*
    002     * Copyright (c) 2007-2014 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
    021    package cascading.operation.filter;
    022
    023    import java.beans.ConstructorProperties;
    024
    025    import cascading.flow.FlowProcess;
    026    import cascading.management.annotation.Property;
    027    import cascading.management.annotation.PropertyDescription;
    028    import cascading.management.annotation.Visibility;
    029    import cascading.operation.BaseOperation;
    030    import cascading.operation.Filter;
    031    import cascading.operation.FilterCall;
    032    import 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     */
    046    public 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      }