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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.

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/*
 * 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.cassandra.gms;

import java.net.InetAddress;

/**
 * This is called by an instance of the IEndpointStateChangePublisher to notify
 * interested parties about changes in the the state associated with any endpoint.
 * For instance if node A figures there is a changes in state for an endpoint B
 * it notifies all interested parties of this change. It is upto to the registered
 * instance to decide what he does with this change. Not all modules maybe interested
 * in all state changes.
 */
public interface IEndpointStateChangeSubscriber
{
    /**
     * Use to inform interested parties about the change in the state
     * for specified endpoint
     *
     * @param endpoint endpoint for which the state change occurred.
     * @param epState  state that actually changed for the above endpoint.
     */
    default void onJoin(InetAddress endpoint, EndpointState epState) {}
    
    default void beforeChange(InetAddress endpoint, EndpointState currentState, ApplicationState newStateKey, VersionedValue newValue) {}

    default void onChange(InetAddress endpoint, ApplicationState state, VersionedValue value) {}

    default void onAlive(InetAddress endpoint, EndpointState state) {}

    default void onDead(InetAddress endpoint, EndpointState state) {}

    default void onRemove(InetAddress endpoint) {}

    /**
     * Called whenever a node is restarted.
     * Note that there is no guarantee when that happens that the node was
     * previously marked down. It will have only if {@code state.isAlive() == false}
     * as {@code state} is from before the restarted node is marked up.
     */
    default void onRestart(InetAddress endpoint, EndpointState state) {}
}