roundrobinstrategy.java

一个用于排队系统仿真的开源软件,有非常形象的图象仿真过程!

/**    
  * Copyright (C) 2006, Laboratorio di Valutazione delle Prestazioni - Politecnico di Milano

  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.

  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.

  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
  
package jmt.engine.NetStrategies.RoutingStrategies;

import jmt.engine.NetStrategies.RoutingStrategy;
import jmt.engine.QueueNet.JobClass;
import jmt.engine.QueueNet.NetNode;
import jmt.engine.QueueNet.NodeList;

/**
 * This class implements a round robin strategy: all the output nodes
 * are chosen in sequence, one at each time; when all the nodes have been chosen,
 * the sequence restarts.
 * @author Francesco Radaelli, Bertoli Marco
 * Modified by Bertoli Marco to correct behaviour with closed classes and sinks
 */
public class RoundRobinStrategy extends RoutingStrategy {
    private int CLOSED_CLASS = JobClass.CLOSED_CLASS;
	private int Counter;

	public RoundRobinStrategy() {
		Counter = 0;
	}

	/**
     * Gets the output node, into which the job must be routed, using a round
     * robin strategy.
     * @param Nodes the list of output nodes
     * @param jobClass class ofcurrent job to be routed
     * @return The selected node.
     */
    public NetNode getOutNode(NodeList Nodes, JobClass jobClass) {
		NetNode out;
		if (Nodes.size() == 0)
			return null;
		else {

            if (Counter == Nodes.size())
				Counter = 0;
			out = Nodes.get(Counter++);

            // Skips sinks for closed classes
            if (jobClass.getType() == CLOSED_CLASS) {
                int totalLoops = 0; // Counts whenever a full loop has been performed
                while (out.isSink()) {
                    if (Counter == Nodes.size()) {
                        Counter = 0;
                        if (totalLoops++ > 0) // An entire loop has been performed... all output nodes are sinks
                            return null;
                    }
                    out = Nodes.get(Counter++);
                }
            }

            return out;
		}
	}
}