multiringnodecollection.java

pastry的java实现的2.0b版

/*************************************************************************

"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

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********************************************************************************/

package rice.p2p.multiring;

import java.util.*;
import rice.p2p.commonapi.*;
import rice.p2p.commonapi.rawserialization.RawMessage;

/**
 * @(#) MultiringNodeCollection.java This class is the class which coordinates
 * all of the nodes on a given host, allowing the nodes to route messages
 * between each other.
 *
 * @version $Id: MultiringNodeCollection.java 3274 2006-05-15 16:17:47Z jeffh $
 * @author Alan Mislove
 */
public class MultiringNodeCollection {

  /**
   * The routing base for ring ids, in bytes
   */
  public int BASE;

  /**
   * The list of nodes in the collection
   */
  protected Vector nodes;

  /**
   * Constructor
   *
   * @param node The node to base this node off of
   * @param BASE DESCRIBE THE PARAMETER
   */
  public MultiringNodeCollection(MultiringNode node, int BASE) {
    this.nodes = new Vector();
    this.nodes.add(node);
    this.BASE = BASE;
  }

  /**
   * This method returns the length of the given ringId
   *
   * @param a The ring Id
   * @return The number of shared bytes
   */
  protected int getLength(RingId a) {
    byte[] ba = a.getRingId().toByteArray();

    for (int i = 0; i < ba.length / BASE; i++) {
      boolean zero = true;

      for (int j = 0; j < BASE; j++) {
        if (ba[ba.length - 1 - (BASE * i + j)] != 0) {
          zero = false;
        }
      }

      if (zero) {
        return i;
      }
    }

    return (ba.length / BASE);
  }

  /**
   * This method returns the length of the shared prefix, in bytes, of the two
   * provided ringIds by comparing the ring values.
   *
   * @param a The first Id
   * @param b The second Id
   * @return The number of shared bytes
   */
  protected int getLengthOfSharedPrefix(RingId a, RingId b) {
    byte[] ba = a.getRingId().toByteArray();
    byte[] bb = b.getRingId().toByteArray();

    for (int i = 0; i < ba.length / BASE; i++) {
      boolean same = true;

      for (int j = 0; j < BASE; j++) {
        if (ba[ba.length - 1 - (BASE * i + j)] != bb[ba.length - 1 - (BASE * i + j)]) {
          same = false;
        }
      }

      if (!same) {
        return i;
      }
    }

    return (ba.length / BASE);
  }

  /**
   * This method allows other nodes to be dynamically added to the node
   * collection. Using this method, a node is added to the collection, and it is
   * told of all of the other nodes in the collection. Similarly, all of the
   * other nodes in the collection are told of this node.
   *
   * @param node The node to add to the collection
   */
  public void addNode(MultiringNode node) {
    if (!node.getNodeId().equals(((MultiringNode) nodes.elementAt(0)).getNodeId())) {
      throw new IllegalArgumentException("Node added does not have the correct nodeId!");
    }

    broadcastNewNode(node);
    nodes.add(node);
  }

  /**
   * This method informs all of the existing nodes of the newly added node, and
   * informs the newly added node of all of the existing nodes.
   *
   * @param node The node that is being added
   */
  protected void broadcastNewNode(MultiringNode node) {
    for (int i = 0; i < nodes.size(); i++) {
      MultiringNode thisNode = (MultiringNode) nodes.elementAt(i);

      if (thisNode.getRingId().equals(node.getRingId())) {
        throw new IllegalArgumentException("ERROR: Attempt to add already-existing ringId " + node + " " + node.getId() + " " + thisNode + " " + thisNode.getId());
      }

      thisNode.nodeAdded(node.getRingId());
      node.nodeAdded(thisNode.getRingId());
    }
  }

  /**
   * This method returns the best next-hop to a given target, using ring
   * hopping, if one exists. Otherwise, if no local node in the collection is
   * the next hop for the target, null is returned.
   *
   * @param id The target id of the message
   * @param message The message to be sent
   * @param application DESCRIBE THE PARAMETER
   */
  protected void route(RingId id, RawMessage message, String application) {
    MultiringNode best = (MultiringNode) nodes.elementAt(0);

    for (int i = 1; i < nodes.size(); i++) {
      MultiringNode thisNode = (MultiringNode) nodes.elementAt(i);
      int bestShared = getLengthOfSharedPrefix((RingId) best.getId(), id);
      int thisShared = getLengthOfSharedPrefix((RingId) thisNode.getId(), id);
      int bestLength = getLength((RingId) best.getId());
      int thisLength = getLength((RingId) thisNode.getId());

      if ((thisShared > bestShared) || ((thisShared == bestShared) && (thisLength < bestLength))) {
        best = thisNode;
      }
    }

    //System.out.println("ROUTING MESSAGE TO TARGET " + id + " VIA NODE " + best.getId());

    best.route(id, message, application);
  }
}