/*
* JBoss, Home of Professional Open Source.
* Copyright 2008, Red Hat Middleware LLC, and individual contributors
* as indicated by the @author tags. See the copyright.txt file in the
* distribution for a full listing of individual contributors.
*
* This 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 (at your option) any later version.
*
* This software 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 software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.jboss.ha.singleton;
import java.util.List;
import org.jboss.ha.framework.interfaces.ClusterNode;
import org.jboss.ha.framework.interfaces.HASingletonElectionPolicy;
import org.jboss.logging.Logger;
/**
* A simple concrete policy service that decides which node in the cluster should be
* the master node to run certain HASingleton service based on attribute "Position".
* The value will be divided by partition size and only remainder will be used.
*
* Let's say partition size is n:
* 0 means the first oldest node.
* 1 means the 2nd oldest node.
* ...
* n-1 means the nth oldest node.
*
* -1 means the youngest node.
* -2 means the 2nd youngest node.
* ...
* -n means the nth youngest node.
*
* E.g. the following attribute says the singleton will be running on the 3rd oldest node of
* the current partition:
* <attribute name="Position">2</attribute>
*
* If no election policy is defined, the oldest node in the cluster runs the
* singleton. This behaivour can be achieved with this policy when "position"
* is set to 0.
*
* @author <a href="mailto:Alex.Fu@novell.com">Alex Fu</a>
* @author <a href="mailto:galder.zamarreno@jboss.com">Galder Zamarreno</a>
* @version $Revision: 108925 $
*/
public class HASingletonElectionPolicySimple
implements HASingletonElectionPolicy, HASingletonElectionPolicySimpleMBean
{
// Attributes
private int mPosition = 0; // Default
private static Logger LOG = Logger.getLogger(HASingletonElectionPolicySimple.class);
/**
* @see HASingletonElectionPolicySimpleMBean#setPosition(int)
*/
public void setPosition(int pos)
{
this.mPosition = pos;
}
/**
* @see HASingletonElectionPolicySimpleMBean#getPosition()
*/
public int getPosition()
{
return this.mPosition;
}
public ClusterNode elect(List<ClusterNode> candidates)
{
int size = candidates.size();
int remainder = ((this.mPosition % size) + size) % size;
ClusterNode result = candidates.get(remainder);
if (LOG.isDebugEnabled())
{
LOG.debug("election with " + size + " nodes and position=" +
mPosition + ", will choose node[" +remainder+"] picked node ip=" +
result.getIpAddress() + " port=" + result.getPort());
}
return result;
}
}