twill-api/src/main/java/org/apache/twill/api/ElectionHandler.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.twill.api;

/**
 * Handles events of election/un-election of leader.
 */
public interface ElectionHandler {

  /**
   * This method will get invoked when a participant becomes a leader in a
   * leader election process. It is guaranteed that this method won't get called
   * consecutively (i.e. called twice or more in a row).
   */
  void leader();

  /**
   * This method will get invoked when a participant is a follower in a
   * leader election process. This method might get called multiple times without
   * the {@link #leader()} method being called.
   */
  void follower();
}