solr/core/src/java/org/apache/solr/cluster/events/ClusterEventProducer.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.solr.cluster.events;

import org.apache.solr.cloud.ClusterSingleton;

import java.io.Closeable;

/**
 * Component that produces {@link ClusterEvent} instances.
 */
public interface ClusterEventProducer extends ClusterSingleton, Closeable {

  /** Unique name for the registration of a plugin-based implementation. */
  String PLUGIN_NAME = ".cluster-event-producer";

  @Override
  default String getName() {
    return PLUGIN_NAME;
  }

  /**
   * Register an event listener for processing the specified event types.
   * @param listener non-null listener. If the same instance of the listener is
   *                 already registered for some event types then it will be also registered
   *                 for additional event types specified in this call.
   * @param eventTypes event types that this listener is being registered for.
   *                   If this is null or empty then all types will be used.
   */
  void registerListener(ClusterEventListener listener, ClusterEvent.EventType... eventTypes);

  /**
   * Unregister an event listener for all event types.
   * @param listener non-null listener.
   */
  default void unregisterListener(ClusterEventListener listener) {
    unregisterListener(listener, ClusterEvent.EventType.values());
  }

  /**
   * Unregister an event listener for specified event types.
   * @param listener non-null listener.
   * @param eventTypes event types from which the listener will be unregistered. If this
   *                   is null or empty then all event types will be used
   */
  void unregisterListener(ClusterEventListener listener, ClusterEvent.EventType... eventTypes);

}