twill-core/src/main/java/org/apache/twill/internal/state/Message.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.twill.internal.state;

import org.apache.twill.api.Command;

/**
 * Represent message objects to communicate between components in Twill.
 */
public interface Message {

  /**
   * Type of message.
   */
  enum Type {
    SYSTEM,
    USER
  }

  /**
   * Scope of the message.
   */
  enum Scope {
    APPLICATION,
    ALL_RUNNABLE,
    RUNNABLE,
    RUNNABLES
  }

  Type getType();

  Scope getScope();

  /**
   * @return the name of the target runnable if scope is {@link Scope#RUNNABLE} or {@code null} otherwise.
   */
  String getRunnableName();

  Command getCommand();
}