runtime/common/src/main/java/org/apache/nemo/runtime/common/message/MessageSender.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;

import java.util.concurrent.CompletableFuture;

/**
 * This class sends messages to {@link MessageListener} with some defined semantics.
 *
 * @param <T> message type
 */
public interface MessageSender<T> {

  /**
   * Send a message to corresponding {@link MessageListener#onMessage}. It does not guarantee whether
   * the message is sent successfully or not.
   *
   * @param message a message
   */
  void send(T message);

  /**
   * Send a message to corresponding {@link MessageListener#onMessageWithContext} and return
   * a reply message. If there was an exception, the returned future would be failed.
   *
   * @param message a message
   * @param <U>     reply message type.
   * @return a future
   */
  <U> CompletableFuture<U> request(T message);

  /**
   * Closes the connection.
   *
   * @throws Exception while closing.
   */
  void close() throws Exception;
}