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* Copyright 2013, Red Hat, Inc., and individual contributors
* as indicated by the @author tags. See the copyright.txt file in the
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*
* 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.wildfly.clustering.singleton.election;
import java.util.List;
import org.wildfly.clustering.group.Node;
import org.wildfly.clustering.singleton.SingletonElectionPolicy;
/**
* A simple concrete policy service that decides which node in the cluster should be the primary 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 behavior 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>
* @author Paul Ferraro
*/
public class SimpleSingletonElectionPolicy implements SingletonElectionPolicy {
private final int position;
public SimpleSingletonElectionPolicy() {
this(0);
}
public SimpleSingletonElectionPolicy(int position) {
this.position = position;
}
@Override
public Node elect(List<Node> candidates) {
int size = candidates.size();
return (size > 0) ? candidates.get(((this.position % size) + size) % size) : null;
}
}