scribepolicy.java

pastry的java实现的2.0b版

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"FreePastry" Peer-to-Peer Application Development Substrate 

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package rice.p2p.scribe;

import java.util.*;

import rice.environment.Environment;
import rice.p2p.commonapi.*;
import rice.p2p.scribe.messaging.*;

/**
 * @(#) ScribePolicy.java This interface represents a policy for Scribe, which
 * is asked whenever a child is about to be added or removed, or when the the
 * local node is about to be implicitly subscribed to a new topic.
 *
 * @version $Id: ScribePolicy.java 2551 2005-06-06 19:01:02Z jeffh $
 * @author Alan Mislove
 */
public interface ScribePolicy {

  /**
   * This method is called when the newChild is about to become our child, and
   * the policy should return whether or not the child should be allowed to
   * become our child. If the length of children and clients is both 0, allowing
   * the child to join will have the effect of implicitly subscribing this node
   * the the given topic.
   *
   * @param message The subscribe message in question
   * @param children The list of children who are currently subscribed to this
   *      topic
   * @param clients The list of clients are are currently subscribed to this
   *      topic
   * @return Whether or not this child should be allowed add.
   */
  public boolean allowSubscribe(SubscribeMessage message, ScribeClient[] clients, NodeHandle[] children);

  /**
   * This method is called when an anycast is received which is not satisfied at
   * the local node. This method should add both the parent and child nodes to
   * the anycast's to-search list, but this method allows different policies
   * concerning the order of the adding as well as selectively adding nodes.
   *
   * @param message The anycast message in question
   * @param parent Our current parent for this message's topic
   * @param children Our current children for this message's topic
   */
  public void directAnycast(AnycastMessage message, NodeHandle parent, NodeHandle[] children);

  /**
   * Informs this policy that a child was added to a topic - the topic is free
   * to ignore this upcall if it doesn't care.
   *
   * @param topic The topic to unsubscribe from
   * @param child The child that was added
   */
  public void childAdded(Topic topic, NodeHandle child);

  /**
   * Informs this policy that a child was removed from a topic - the topic is
   * free to ignore this upcall if it doesn't care.
   *
   * @param topic The topic to unsubscribe from
   * @param child The child that was removed
   */
  public void childRemoved(Topic topic, NodeHandle child);

  /**
   * The default policy for Scribe, which always allows new children to join and
   * adds children in the order in which they are provided, implicitly providing
   * a depth-first search.
   *
   * @version $Id: ScribePolicy.java 2551 2005-06-06 19:01:02Z jeffh $
   * @author amislove
   */
  public static class DefaultScribePolicy implements ScribePolicy {
    /**
     * DESCRIBE THE FIELD
     */
    protected Environment environment;

    /**
     * Constructor for DefaultScribePolicy.
     *
     * @param env DESCRIBE THE PARAMETER
     */
    public DefaultScribePolicy(Environment env) {
      environment = env;
    }

    /**
     * This method always return true;
     *
     * @param message The subscribe message in question
     * @param children The list of children who are currently subscribed
     * @param clients The list of clients are are currently subscribed
     * @return True.
     */
    public boolean allowSubscribe(SubscribeMessage message, ScribeClient[] clients, NodeHandle[] children) {
      return true;
    }

    /**
     * Simply adds the parent and children in order, which implements a
     * depth-first-search.
     *
     * @param message The anycast message in question
     * @param parent Our current parent for this message's topic
     * @param children Our current children for this message's topic
     */
    public void directAnycast(AnycastMessage message, NodeHandle parent, NodeHandle[] children) {
      if (parent != null) {
        message.addLast(parent);
      }

      // now randomize the children list
      for (int i = 0; i < children.length; i++) {
        int j = environment.getRandomSource().nextInt(children.length);
        int k = environment.getRandomSource().nextInt(children.length);
        NodeHandle tmp = children[j];
        children[j] = children[k];
        children[k] = tmp;
      }

      for (int l = 0; l < children.length; l++) {
        message.addFirst(children[l]);
      }
    }

    /**
     * Informs this policy that a child was added to a topic - the topic is free
     * to ignore this upcall if it doesn't care.
     *
     * @param topic The topic to unsubscribe from
     * @param child The child that was added
     */
    public void childAdded(Topic topic, NodeHandle child) {
    }

    /**
     * Informs this policy that a child was removed from a topic - the topic is
     * free to ignore this upcall if it doesn't care.
     *
     * @param topic The topic to unsubscribe from
     * @param child The child that was removed
     */
    public void childRemoved(Topic topic, NodeHandle child) {
    }
  }

  /**
   * An optional policy for Scribe, which allows up to a specified number of
   * children per topic.
   *
   * @version $Id: ScribePolicy.java 2551 2005-06-06 19:01:02Z jeffh $
   * @author amislove
   */
  public static class LimitedScribePolicy extends DefaultScribePolicy {

    /**
     * The number of children to allow per topic
     */
    protected int maxChildren;

    /**
     * Construtor which takes a maximum number
     *
     * @param max The maximum number of children
     * @param env DESCRIBE THE PARAMETER
     */
    public LimitedScribePolicy(int max, Environment env) {
      super(env);
      this.maxChildren = max;
    }

    /**
     * This method returns (children.length < maxChildren-1);
     *
     * @param message The subscribe message in question
     * @param children The list of children who are currently subscribed
     * @param clients The list of clients are are currently subscribed
     * @return True.
     */
    public boolean allowSubscribe(SubscribeMessage message, ScribeClient[] clients, NodeHandle[] children) {
      return (children.length < (maxChildren - 1));
    }
  }
}