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A RMI-like distributed computing framework

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package org.sapia.ubik.rmi.replication;

import org.sapia.ubik.net.ServerAddress;

import java.util.Set;


/**
 * This class implements the logic that selects the next server to which a replicated command
 * should be dispatched.
 *
 * @author Yanick Duchesne
 * 
 * Copyright:
Copyright © 2002-2004 Sapia Open Source Software. All Rights Reserved.
 * License:
Read the license.txt file of the jar or visit the
 *        license page at the Sapia OSS web site
 * 
 */
public class ReplicationStrategy {
  private Set _visited;
  private Set _targets;
  private Set _siblings;

  /**
   * @param visited the Set of ServerAddresses of the hosts
   * that have already been visited.
   * @param targets the Set of ServerAddresses corresponding to
   * targeted hosts - if null, then the strategy assumes that all hosts must
   * be visited.
   * @param existing the Set of ServerAddresses corresponding to
   * the existing hosts.
   */
  public ReplicationStrategy(Set visited, Set targets, Set existing) {
    _visited    = visited;
    _targets    = targets;
    _siblings   = existing;
  }

  /**
   * @return the ServerAddress of the next sibling host to which replication
   * should be made. null is returned if there is no "next" host to which to
   * replicate - all hosts have been visited. Note: if not null, the returned address
   * is added to the set of visited ones.
   */
  public ServerAddress selectNextSibling() {
    ServerAddress toReturn;

    if (_targets == null) {
      _siblings.removeAll(_visited);

      if (_siblings.size() == 0) {
        return null;
      }

      toReturn = (ServerAddress) _siblings.iterator().next();
    } else {
      _siblings.retainAll(_targets);
      _siblings.removeAll(_visited);

      if (_siblings.size() == 0) {
        return null;
      }

      toReturn = (ServerAddress) _siblings.iterator().next();
    }

    _visited.add(toReturn);

    return toReturn;
  }
}