FixedStreamRateDriverSpout.java

/*
 * #!
 * %
 * Copyright (C) 2014 - 2016 Humboldt-Universität zu Berlin
 * %
 * 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 de.hub.cs.dbis.aeolus.spouts;

import java.util.Map;

import backtype.storm.spout.SpoutOutputCollector;
import backtype.storm.task.TopologyContext;
import backtype.storm.topology.IRichSpout;
import backtype.storm.topology.OutputFieldsDeclarer;





/**
 * {@link FixedStreamRateDriverSpout} wraps a working spout (with high output rate) and assures a stable (lower) output
 * data rate. In order to simulate that the working spout is working, busy wait strategy is used.
 * 
 * @author mjsax
 */
public class FixedStreamRateDriverSpout implements IRichSpout {
	private final static long serialVersionUID = 5846769281188227304L;
	
	/** The original spout that produces output tuples. */
	private IRichSpout wrappedSpout;
	
	/** The delay between two consecutive emits in nano seconds (ie, the inverse of the intended output rate). */
	private final long delay;
	
	/** The system timestamp when the next tuple will be emitted. */
	private long nextTS;
	
	
	
	/**
	 * Instantiates a new {@link FixedStreamRateDriverSpout} for the given spout and output rate.
	 * 
	 * @param spout
	 *            The working spout.
	 * @param outputRate
	 *            The output rate in tuples per second.
	 */
	public FixedStreamRateDriverSpout(IRichSpout spout, double outputRate) {
		assert (spout != null);
		assert (outputRate > 0);
		
		this.wrappedSpout = spout;
		this.delay = (long)((1000 * 1000 * 1000) / outputRate);
	}
	
	@Override
	public void open(@SuppressWarnings("rawtypes") Map conf, TopologyContext context, SpoutOutputCollector collector) {
		this.wrappedSpout.open(conf, context, collector);
	}
	
	@Override
	public void close() {
		this.wrappedSpout.close();
	}
	
	@Override
	public void activate() {
		this.wrappedSpout.activate();
		// we can emit the first tuple right away
		this.nextTS = System.nanoTime();
	}
	
	@Override
	public void deactivate() {
		this.wrappedSpout.deactivate();
	}
	
	@Override
	public void nextTuple() {
		while(System.nanoTime() < this.nextTS) {
			// busy wait
		}
		this.wrappedSpout.nextTuple();
		this.nextTS += this.delay;
	}
	
	@Override
	public void ack(Object msgId) {
		this.wrappedSpout.ack(msgId);
	}
	
	@Override
	public void fail(Object msgId) {
		this.wrappedSpout.fail(msgId);
	}
	
	@Override
	public void declareOutputFields(OutputFieldsDeclarer declarer) {
		this.wrappedSpout.declareOutputFields(declarer);
	}
	
	@Override
	public Map<String, Object> getComponentConfiguration() {
		return this.wrappedSpout.getComponentConfiguration();
	}
	
}