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/*
 * Copyright (c) 2010-2015 Pivotal Software, Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you
 * may not use this file except in compliance with the License. You
 * may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License. See accompanying
 * LICENSE file.
 */
package com.gemstone.gemfire.distributed.internal;


/**
 * This class is a test hook to intercept DistributionMessages in the
 * VM receiving the message.
 * 
 * @author dsmith
 *
 */
public abstract class DistributionMessageObserver {
  
  private static DistributionMessageObserver instance;
  
  /**
   * Set the instance of the observer. Setting to null will clear the observer.
   * @param instance
   * @return the old observer, or null if there was no old observer.
   */
  public static final DistributionMessageObserver setInstance(DistributionMessageObserver instance) {
    DistributionMessageObserver oldInstance = DistributionMessageObserver.instance;
    DistributionMessageObserver.instance = instance;
    return oldInstance;
  }
  
  public static final DistributionMessageObserver getInstance() {
    return instance;
  }
  
  /**
   * Called before a the process method of the DistributionMessage is called
   * @param dm the distribution manager that received the message
   * @param message The message itself
   */
  public void beforeProcessMessage(DistributionManager dm,
      DistributionMessage message) {
    
  }

  /**
   * Called after the process method of the DistributionMessage is called
   * @param dm the distribution manager that received the message
   * @param message The message itself
   */
  public void afterProcessMessage(DistributionManager dm,
      DistributionMessage message) {
    
  }

  /**
   * Called just before a message is distributed.
   * @param dm the distribution manager that's sending the messsage
   * @param msg the message itself
   */
  public void beforeSendMessage(DistributionManager dm,
      DistributionMessage msg) {
    
  }
}