/*
 * 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.flink.agents.runtime.message;

import java.io.Serializable;
import java.util.OptionalLong;

/** Message interface, used to represent messages sent between flink-agents operators. */
public interface Message extends Serializable {
    /**
     * isBarrierMessage - returns an empty optional for non barrier messages or wrapped checkpointId
     * for barrier messages.
     *
     * <p>When this message represents a checkpoint barrier, this method returns an {@code Optional}
     * of a checkpoint id that produced that barrier. For other types of messages (i.e. {@code
     * Payload}) this method returns an empty {@code Optional}.
     */
    OptionalLong isBarrierMessage();
}
