modules/core/src/main/java/org/apache/ignite/internal/processors/metastorage/DistributedMetaStorageListener.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.ignite.internal.processors.metastorage;

import java.io.Serializable;
import java.util.function.Predicate;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

/**
 * Listener for distributed metastorage data updates.
 *
 * @see ReadableDistributedMetaStorage#listen(Predicate, DistributedMetaStorageListener)
 */
@FunctionalInterface
public interface DistributedMetaStorageListener<T extends Serializable> {
    /**
     * Invoked in two cases:
     * <ul>
     *     <li>data was dynamicaly updated;</li>
     *     <li>node was started. In this case {@code oldVal} and {@code newVal} might be different only if new data
     *     was received from cluster</li>
     * </ul>
     *
     * @param key The key.
     * @param oldVal Previous value associated with the key.
     * @param newVal New value after update.
     */
    void onUpdate(@NotNull String key, @Nullable T oldVal, @Nullable T newVal);
}