    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.flow.stream.element;
    022
    023import java.util.concurrent.atomic.AtomicInteger;
    024
    025import cascading.flow.FlowElement;
    026import cascading.flow.FlowProcess;
    027import cascading.flow.stream.duct.Collapsing;
    028import cascading.flow.stream.duct.Duct;
    029import cascading.flow.stream.graph.StreamGraph;
    030import cascading.tuple.TupleEntry;
    031
    032/**
    033 *
    034 */
    035public class MergeStage extends ElementStage<TupleEntry, TupleEntry> implements Collapsing
    036  {
    037  private boolean started = false;
    038  protected final AtomicInteger completeCount = new AtomicInteger( 0 );
    039  private int numIncomingPaths;
    040
    041  public MergeStage( FlowProcess flowProcess, FlowElement flowElement )
    042    {
    043    super( flowProcess, flowElement );
    044    }
    045
    046  @Override
    047  public void bind( StreamGraph streamGraph )
    048    {
    049    super.bind( streamGraph );
    050
    051    numIncomingPaths = streamGraph.findAllPreviousFor( this ).length;
    052    }
    053
    054  @Override
    055  public void initialize()
    056    {
    057    super.initialize();
    058
    059    completeCount.set( numIncomingPaths );
    060    }
    061
    062  @Override
    063  public synchronized void start( Duct previous )
    064    {
    065    if( started )
    066      return;
    067
    068    super.start( previous );
    069    started = true;
    070    }
    071
    072  @Override
    073  public void complete( Duct previous )
    074    {
    075    if( completeCount.decrementAndGet() != 0 )
    076      return;
    077
    078    super.complete( previous );
    079    completeCount.set( numIncomingPaths );
    080    }
    081  }