nodehandle.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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- Redistributions of source code must retain the above copyright
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- Redistributions in binary form must reproduce the above copyright
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- Neither  the name  of Rice  University (RICE) nor  the names  of its
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This software is provided by RICE and the contributors on an "as is"
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********************************************************************************/

package rice.pastry;

import rice.environment.logging.Logger;
import rice.p2p.commonapi.rawserialization.OutputBuffer;
import rice.pastry.messaging.*;

import java.io.*;
import java.util.*;

/**
 * Interface for handles to remote nodes.
 *
 * @version $Id: NodeHandle.java 3274 2006-05-15 16:17:47Z jeffh $
 * @author Andrew Ladd
 */
public abstract class NodeHandle extends rice.p2p.commonapi.NodeHandle {

  // the local pastry node
  /**
   * DESCRIBE THE FIELD
   */
  protected transient PastryNode localnode;
  /**
   * DESCRIBE THE FIELD
   */
  protected transient Logger logger;

  /**
   * DESCRIBE THE FIELD
   */
  public final static int LIVENESS_ALIVE = 1;
  /**
   * DESCRIBE THE FIELD
   */
  public final static int LIVENESS_SUSPECTED = 2;
  /**
   * DESCRIBE THE FIELD
   */
  public final static int LIVENESS_DEAD = 3;

  final static long serialVersionUID = 987479397660721015L;

  /**
   * Gets the nodeId of this Pastry node.
   *
   * @return the node id.
   */
  public abstract Id getNodeId();

  /**
   * Gets the Id attribute of the NodeHandle object
   *
   * @return The Id value
   */
  public rice.p2p.commonapi.Id getId() {
    return getNodeId();
  }

  /**
   * Returns the last known liveness information about the Pastry node
   * associated with this handle. Invoking this method does not cause network
   * activity.
   *
   * @return true if the node is alive, false otherwise.
   */
  public final boolean isAlive() {
    return getLiveness() < LIVENESS_DEAD;
  }

  /**
   * A more detailed version of isAlive(). This can return 3 states:
   *
   * @return LIVENESS_ALIVE, LIVENESS_SUSPECTED, LIVENESS_DEAD
   */
  public abstract int getLiveness();

  /**
   * Accessor method.
   *
   * @return The LocalNode value
   */
  public final PastryNode getLocalNode() {
    return localnode;
  }

  /**
   * Method which FORCES a check of liveness of the remote node. Note that this
   * method should ONLY be called by internal Pastry maintenance algorithms -
   * this is NOT to be used by applications. Doing so will likely cause a blowup
   * of liveness traffic.
   *
   * @return true if node is currently alive.
   */
  public boolean checkLiveness() {
    return ping();
  }

  /**
   * Returns the last known proximity information about the Pastry node
   * associated with this handle. Invoking this method does not cause network
   * activity. Smaller values imply greater proximity. The exact nature and
   * interpretation of the proximity metric implementation-specific.
   *
   * @return the proximity metric value
   */
  public abstract int proximity();

  /**
   * Ping the node. Refreshes the cached liveness status and proximity value of
   * the Pastry node associated with this. Invoking this method causes network
   * activity.
   *
   * @return true if node is currently alive.
   */
  public abstract boolean ping();

//  transient Exception ctor;
//  public NodeHandle() {
//    ctor = new Exception("ctor");
//  }

  /**
   * May be called from handle etc methods to ensure that local node has been
   * set, either on construction or on deserialization/receivemsg.
   */
  public void assertLocalNode() {
    if (localnode == null) {
//      ctor.printStackTrace();
      throw new RuntimeException("PANIC: localnode is null in " + this + "@" + System.identityHashCode(this));
    }
  }

  /**
   * Equality operator for nodehandles.
   *
   * @param obj a nodehandle object
   * @return true if they are equal, false otherwise.
   */
  public abstract boolean equals(Object obj);

  /**
   * Method which is used by Pastry to start the bootstrapping process on the
   * local node using this handle as the bootstrap handle. Default behavior is
   * simply to call receiveMessage(msg), but transport layer implementations may
   * care to perform other tasks by overriding this method, since the node is
   * not technically part of the ring yet.
   *
   * @param msg the bootstrap message.
   * @throws IOException
   */
  public void bootstrap(Message msg) throws IOException {
    receiveMessage(msg);
  }

  /**
   * Hash codes for nodehandles.
   *
   * @return a hash code.
   */
  public abstract int hashCode();

  /**
   * DESCRIBE THE METHOD
   *
   * @param msg DESCRIBE THE PARAMETER
   */
  public abstract void receiveMessage(Message msg);

  /**
   * DESCRIBE THE METHOD
   *
   * @param buf DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public abstract void serialize(OutputBuffer buf) throws IOException;
}