runtime/common/src/main/java/org/apache/nemo/runtime/common/message/MessageListener.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */
package org.apache.nemo.runtime.common.message;


/**
 * Handles messages from {@link MessageSender}. Multiple MessageListeners can be setup using {@link MessageEnvironment}
 * while they are identified by their unique message type ids.
 *
 * @param <T> message type
 */
public interface MessageListener<T> {

  /**
   * Called back when a message is received.
   *
   * @param message a message
   */
  void onMessage(T message);

  /**
   * Called back when a message is received, and return a response using {@link MessageContext}.
   *
   * @param message        a message
   * @param messageContext a message context
   */
  void onMessageWithContext(T message, MessageContext messageContext);

}