CreateTableRoundRobin.java

/**
 * C-JDBC: Clustered JDBC.
 * Copyright (C) 2002-2005 French National Institute For Research In Computer
 * Science And Control (INRIA).
 * Contact: c-jdbc@objectweb.org
 * 
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation; either version 2.1 of the License, or any later
 * version.
 * 
 * This library 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 Lesser General Public License
 * for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
 *
 * Initial developer(s): Emmanuel Cecchet.
 * Contributor(s): Jean-Bernard van Zuylen
 */

package org.objectweb.cjdbc.controller.loadbalancer.policies.createtable;

import java.util.ArrayList;

/**
 * Implements a round-robin strategy for <code>CREATE TABLE</code>
 * statements.
 * 
 * @author <a href="mailto:Emmanuel.Cecchet@inria.fr">Emmanuel Cecchet</a>
 * @author <a href="mailto:jbvanzuylen@transwide.com">Jean-Bernard van Zuylen
 *         </a>
 * @version 1.0
 */
public class CreateTableRoundRobin extends CreateTableRule
{
  private int index = 0;

  /**
   * Creates a new <code>CreateTableRoundRobin</code>.
   */
  public CreateTableRoundRobin()
  {
    super(CreateTablePolicy.ROUND_ROBIN);
  }

  /**
   * Creates a new <code>CreateTableRoundRobin</code>.
   * 
   * @param backendList <code>ArrayList</code> of <code>DatabaseBackend</code>
   */
  public CreateTableRoundRobin(ArrayList backendList)
  {
    super(CreateTablePolicy.ROUND_ROBIN, backendList);
  }

  /**
   * @see org.objectweb.cjdbc.controller.loadbalancer.policies.createtable.CreateTableRule#getBackends(ArrayList)
   */
  public ArrayList getBackends(ArrayList backends) throws CreateTableException
  {
    if (nbOfNodes == 0)
      return null;
    
    ArrayList clonedList = super.getBackends(backends);
    
    int clonedSize = clonedList.size();

    if (nbOfNodes == clonedSize)
      return clonedList;
    else if (nbOfNodes > clonedSize)
      throw new CreateTableException(
        "Asking for more backends ("
          + nbOfNodes
          + ") than available ("
          + clonedSize
          + ")");

    ArrayList result = new ArrayList(nbOfNodes);

    synchronized (this)
    { // index must be modified in mutual exclusion
      for (int i = 0; i < nbOfNodes; i++)
      {
        index = (index + 1) % clonedSize;
        if (index - i < 0)
          result.add(clonedList.remove(0));
        else
          result.add(clonedList.remove(index - i));
      }
    }

    return result;
  }

  /**
   * @see org.objectweb.cjdbc.controller.loadbalancer.policies.createtable.CreateTableRule#getInformation()
   */
  public String getInformation()
  {
    String s;
    if (tableName == null)
      s = "Default rule create table on ";
    else
      s = "Rule for table " + tableName + " create table on ";

    return s + nbOfNodes + " node(s) in round-robin from " + backendList;
  }
}

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