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

"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

- Neither  the name  of Rice  University (RICE) nor  the names  of its
contributors may be  used to endorse or promote  products derived from
this software without specific prior written permission.

This software is provided by RICE and the contributors on an "as is"
basis, without any representations or warranties of any kind, express
or implied including, but not limited to, representations or
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particular purpose. In no event shall RICE or contributors be liable
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consequential damages (including, but not limited to, procurement of
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whether in contract, strict liability, or tort (including negligence
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if advised of the possibility of such damage.

********************************************************************************/
package rice.p2p.aggregation;

/**
 * @(#) Aggregation.java This interface is exported by all instances of the
 * Aggregation service, in addition to the Past and GCPast interfaces. The
 * additional functions are used mainly to recover from failures, i.e. cases in
 * which the service loses its local metadata.
 *
 * @version $Id: Aggregation.java 1764 2004-07-22 15:36:45Z ahae $
 * @author Andreas Haeberlen
 */

import java.io.Serializable;
import rice.Continuation;
import rice.p2p.commonapi.Id;

/**
 * DESCRIBE THE INTERFACE
 *
 * @version $Id: pretty.settings 2305 2005-03-11 20:22:33Z jeffh $
 * @author jeffh
 */
public interface Aggregation {

  /**
   * Fetches the handle object. This object is important in the event of a
   * failure that causes Aggregation to lose its local metadata cache. When the
   * handle object is later restored via setHandle(), Aggregation can recover
   * all objects that have been aggregated prior to the getHandle() call, except
   * objects that have already expired. Note that this does not include objects
   * that were still in the local buffer when the failure occurred. To prevent
   * data loss, it is recommended to invoke flush() before fetching the handle
   * object.
   *
   * @return the current handle object
   */
  public Serializable getHandle();

  /**
   * Restores the handle object. This method should always be invoked at
   * startup, using the most current handle object available. When the
   * continuation is invoked, all non-expired objects linked to the handle are
   * accessible from the local node.
   *
   * @param handle the handle object
   * @param command Command to be performed when the method completes.
   */
  public void setHandle(Serializable handle, Continuation command);

  /**
   * Creates an aggregate that includes the most current object with the
   * specified key. When the continuation is invoked, the object is persistent
   * and linked to the current handle object.
   *
   * @param id the key of the object to be made persistent.
   * @param command Command to be performed when the method completes.
   */
  public void flush(Id id, Continuation command);

  /**
   * Creates aggregates from all objects in the local object cache. When the
   * continuation is invoked, all objects that were inserted prior to flush()
   * are persistent and linked to the current handle object.
   *
   * @param command Command to be performed when the method completes.
   */
  public void flush(Continuation command);

  /**
   * Attempts to retrieve the most recent object that has been inserted by the
   * local node under the specified key. This is useful when the object has been
   * overwritten by an attacker. This method may fail or return an outdated
   * version of the object if a) the object is not linked to the current handle,
   * or b) the object was never aggregated because of the aggregation policy.
   *
   * @param id the key of the object to be retrieved
   * @param command Command to be performed when the method completes.
   */
  public void rollback(Id id, Continuation command);

  /**
   * Deletes all local state, including the aggregate list and all objects
   * waiting in the local buffer. This is useful when the local instance appears
   * to have been corrupted or tampered with. The state can be recovered by
   * invoking setHandle() with an earlier handle object, and by using rollback()
   * on objects that appear to have been overwritten.
   *
   * @param command Command to be performed when the method completes.
   */
  public void reset(Continuation command);

}

