MapDriver.java

/***********************************************************************************************************************
 *
 * Copyright (C) 2010 by the Stratosphere project (http://stratosphere.eu)
 *
 * Licensed 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 eu.stratosphere.pact.runtime.task;

import eu.stratosphere.pact.common.generic.GenericMapper;
import eu.stratosphere.pact.common.stubs.Collector;
import eu.stratosphere.pact.common.stubs.MapStub;
import eu.stratosphere.pact.common.util.MutableObjectIterator;

/**
 * Map task which is executed by a Nephele task manager. The task has a single
 * input and one or multiple outputs. It is provided with a MapStub
 * implementation.
 * <p>
 * The MapTask creates an iterator over all key-value pairs of its input and hands that to the <code>map()</code> method
 * of the MapStub.
 * 
 * @see MapStub
 * @see GenericMapper
 * @author Fabian Hueske
 * @author Stephan Ewen
 * 
 * @param <IT> The mapper's input data type.
 * @param <OT> The mapper's output data type.
 */
public class MapDriver<IT, OT> implements PactDriver<GenericMapper<IT, OT>, OT>// extends AbstractPactTask<GenericMapper<IT, OT>, OT>
{
	private PactTaskContext<GenericMapper<IT, OT>, OT> taskContext;
	
	private volatile boolean running;
	
	
	/* (non-Javadoc)
	 * @see eu.stratosphere.pact.runtime.task.PactDriver#setup(eu.stratosphere.pact.runtime.task.PactTaskContext)
	 */
	@Override
	public void setup(PactTaskContext<GenericMapper<IT, OT>, OT> context) {
		this.taskContext = context;
		this.running = true;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see eu.stratosphere.pact.runtime.task.AbstractPactTask#getNumberOfInputs()
	 */
	@Override
	public int getNumberOfInputs() {
		return 1;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see eu.stratosphere.pact.runtime.task.AbstractPactTask#getStubType()
	 */
	@Override
	public Class<GenericMapper<IT, OT>> getStubType() {
		@SuppressWarnings("unchecked")
		final Class<GenericMapper<IT, OT>> clazz = (Class<GenericMapper<IT, OT>>) (Class<?>) GenericMapper.class;
		return clazz;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see eu.stratosphere.pact.runtime.task.AbstractPactTask#requiresComparatorOnInput()
	 */
	@Override
	public boolean requiresComparatorOnInput() {
		return false;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see eu.stratosphere.pact.runtime.task.AbstractPactTask#prepare()
	 */
	@Override
	public void prepare() throws Exception {
		// nothing, since a mapper does not need any preparation
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see eu.stratosphere.pact.runtime.task.AbstractPactTask#run()
	 */
	@Override
	public void run() throws Exception
	{
		// cache references on the stack
		final MutableObjectIterator<IT> input = this.taskContext.getInput(0);
		final GenericMapper<IT, OT> stub = this.taskContext.getStub();
		final Collector<OT> output = this.taskContext.getOutputCollector();

		final IT record = this.taskContext.<IT>getInputSerializer(0).createInstance();

		while (this.running && input.next(record)) {
			stub.map(record, output);
		}
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see eu.stratosphere.pact.runtime.task.AbstractPactTask#cleanup()
	 */
	@Override
	public void cleanup() throws Exception {
		// mappers need no cleanup, since no strategies are used.
	}

	/* (non-Javadoc)
	 * @see eu.stratosphere.pact.runtime.task.PactDriver#cancel()
	 */
	@Override
	public void cancel() {
		this.running = false;
	}
}