/*
 * 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.runtime.heartbeat;

import org.apache.flink.runtime.clusterframework.types.ResourceID;
import org.apache.flink.runtime.concurrent.Future;

/**
 * Interface for the interaction with the {@link HeartbeatManager}. The heartbeat listener is used
 * for the following things:
 * <p>
 * <ul>
 *     <il>Notifications about heartbeat timeouts</il>
 *     <li>Payload reports of incoming heartbeats</li>
 *     <li>Retrieval of payloads for outgoing heartbeats</li>
 * </ul>
 * @param <I> Type of the incoming payload
 * @param <O> Type of the outgoing payload
 */
public interface HeartbeatListener<I, O> {

	/**
	 * Callback which is called if a heartbeat for the machine identified by the given resource
	 * ID times out.
	 *
	 * @param resourceID Resource ID of the machine whose heartbeat has timed out
	 */
	void notifyHeartbeatTimeout(ResourceID resourceID);

	/**
	 * Callback which is called whenever a heartbeat with an associated payload is received. The
	 * carried payload is given to this method.
	 *
	 * @param resourceID Resource ID identifying the sender of the payload
	 * @param payload Payload of the received heartbeat
	 */
	void reportPayload(ResourceID resourceID, I payload);

	/**
	 * Retrieves the payload value for the next heartbeat message. Since the operation can happen
	 * asynchronously, the result is returned wrapped in a future.
	 *
	 * @return Future containing the next payload for heartbeats
	 */
	Future<O> retrievePayload();
}