synchronization/changelog/ChangelogIterator.java

	ChangelogIterator.java revision f71f7a61dec7c9089378d14493ad564a1dedf0b5
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at
 * trunk/opends/resource/legal-notices/OpenDS.LICENSE
 * or https://OpenDS.dev.java.net/OpenDS.LICENSE.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at
 * trunk/opends/resource/legal-notices/OpenDS.LICENSE.  If applicable,
 * add the following below this CDDL HEADER, with the fields enclosed
 * by brackets "[]" replaced with your own identifying information:
 *      Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 *
 *
 *      Portions Copyright 2006-2007 Sun Microsystems, Inc.
 */
package org.opends.server.synchronization.changelog;

import com.sleepycat.je.DatabaseException;

import org.opends.server.synchronization.changelog.ChangelogDB.ChangelogCursor;
import org.opends.server.synchronization.common.ChangeNumber;
import org.opends.server.synchronization.protocol.UpdateMessage;

/**
 * This class allows to iterate through the changes received from a given
 * LDAP Server Identifier.
 */
public class ChangelogIterator
{
  private UpdateMessage currentChange = null;
  private ChangelogCursor cursor = null;

  /**
   * Creates a new ChangelogIterator.
   * @param id the Identifier of the server on which the iterator applies.
   * @param db The db where the iterator must be created.
   * @param changeNumber The ChangeNumber after which the iterator must start.
   * @throws Exception If there is no other change to push after change
   *         with changeNumber number.
   * @throws DatabaseException if a database problem happened.
   */
  public ChangelogIterator(short id, ChangelogDB db, ChangeNumber changeNumber)
                           throws Exception, DatabaseException
  {
    cursor = db.openReadCursor(changeNumber);
    if (cursor == null)
      throw new Exception("no new change");
     if (this.next() == false)
     {
       cursor.close();
       cursor = null;
       throw new Exception("no new change");
     }
  }

  /**
   * Get the UpdateMessage where the iterator is currently set.
   * @return The UpdateMessage where the iterator is currently set.
   */
  public UpdateMessage getChange()
  {
    return currentChange;
  }

  /**
   * Go to the next change in the ChangelogDB or in the server Queue.
   * @return false if the iterator is already on the last change before
   *         this call.
   */
  public boolean next()
  {
    currentChange = cursor.next();

    if (currentChange != null)
      return true;
    else
    {
      // TODO : should check here if some changes are still in the
      // dbHandler message queue and not yet saved to the backing database
      // if yes should get change from there from now on.
      return false;
    }

  }

  /**
   * Release the resources and locks used by this Iterator.
   * This method must be called when the iterator is no longer used.
   * Failure to do it could cause DB deadlock.
   */
  public void releaseCursor()
  {
    synchronized (this)
    {
      if (cursor != null)
      {
        cursor.close();
        cursor = null;
      }
    }
  }

  /**
   * Called by the Gc when the object is garbage collected
   * Release the cursor in case the iterator was badly used and releaseCursor
   * was never called.
   */
  protected void finalize()
  {
    releaseCursor();
  }
}