/*************************************************************************
 * Copyright 2009-2012 Eucalyptus Systems, Inc.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 3 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see http://www.gnu.org/licenses/.
 *
 * Please contact Eucalyptus Systems, Inc., 6755 Hollister Ave., Goleta
 * CA 93117, USA or visit http://www.eucalyptus.com/licenses/ if you need
 * additional information or have any questions.
 *
 * This file may incorporate work covered under the following copyright
 * and permission notice:
 *
 *   Software License Agreement (BSD License)
 *
 *   Copyright (c) 2008, Regents of the University of California
 *   All rights reserved.
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 ************************************************************************/

package com.eucalyptus.util.async;

import com.eucalyptus.util.Callback;
import edu.ucsb.eucalyptus.msgs.BaseMessage;

/**
 * An asynchronous callback which involves remote communication (read: possibly long lasting). Implementors of this interface are guaranteed that:
 * 
 * <ul>
 * <li>{@link #initialize(BaseMessage)} will be invoked before communication begins.</li>
 * <li>Should the invokation of {@link #initialize(BaseMessage)} terminate prematurely the callback will be disposed of -- preconditions
 * caused a failure.</li>
 * <li>Otherwise, either {@link #fire(BaseMessage)} <b>OR</b> {@link #fireException(Throwable)} will be called exactly
 * one time.</li>
 * <li>The argument to {@link #fire(BaseMessage)}/{@link #fireException(Throwable)} will be the outcome of the remote
 * operation.</li>
 * </ul>
 * @see Callback
 * @see Callback.Checked
 * @see Callback.TwiceChecked
 * @see RemoteCallback#fire(BaseMessage)
 * @see RemoteCallback#fireException(Throwable)
 */
public interface RemoteCallback<Q extends BaseMessage, R extends BaseMessage> extends Callback.TwiceChecked<Q, R> {
  
  /**
   * Get the request being made by this callback.
   */
  Q getRequest( );
  
  /**
   * Initialize (e.g., check preconditions) before proceeding with the
   * connection and sending of <tt>request</tt>. Guaranteed to be called only
   * once per corresponding dispatch.
   */
  @Override
  void initialize( Q request ) throws Exception;
  
  /**
   * The operation completed with a response: <tt>msg</tt>.
   */
  @Override
  void fire( R msg );
  
  /**
   * The operation completed with an exception.
   */
  @Override
  void fireException( Throwable t );
  
}