junkaixue commented on code in PR #2488: URL: https://github.com/apache/helix/pull/2488#discussion_r1197011508
########## meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionClient.java: ########## @@ -0,0 +1,180 @@ +package org.apache.helix.metaclient.recipes.leaderelection; + +/* + * 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. + */ + +import java.util.List; + +import org.apache.helix.metaclient.api.MetaClientInterface; +import org.apache.helix.metaclient.factories.MetaClientConfig; + + +/** + * LeaderElectionClient does distributed leader election using CRUD and change notification APIs + * provided by underlying metadata client. Leader election config can provide many + * configs like base path for all participating nodes, sync/async mode, TTL etc. + * + * Participants join a leader election group by calling the following API. + * The Leader Election client maintains and elect an active leader from participant pool. + * All participants wanted to be elected as leader joins a pool. + * LeaderElection client maintains an active leader, by monitoring liveness of current leader and + * re-elect if needed and user no need to call elect or re-elect explicitly. + * This LeaderElection client will notify registered listeners for any leadership change. + */ +public class LeaderElectionClient { + + /** + * Construct a LeaderElectionClient using a user passed in leaderElectionConfig. It creates a MetaClient + * instance underneath. + * When MetaClient is auto closed be cause of being disconnected and auto retry connection timed out, A new + * MetaClient instance will be created and keeps retry connection. + * + * @param metaClientConfig The config used to create an metaclient. + */ + public LeaderElectionClient(MetaClientConfig metaClientConfig) { + + } + + /** + * Construct a LeaderElectionClient using a user passed in MetaClient object + * When MetaClient is auto closed be cause of being disconnected and auto retry connection timed out, user + * will need to create a new MetaClient and a new LeaderElectionClient instance. + * + * @param metaClient metaClient object to be used. + */ + public LeaderElectionClient(MetaClientInterface metaClient) { + + } + + /** + * Returns true if current participant is the current leadership. + */ + public boolean isLeader(String leaderPath, String participant) { + return false; + } + + /** + * Participants join a leader election group by calling the following API. + * The Leader Election client maintains and elect an active leader from the participant pool. + * + * @param leaderPath The path for leader election. + * @param participant The participant name to join pool. + * @return boolean indicating if the operation is succeeded. + */ + public boolean joinLeaderElectionParticipantPool(String leaderPath, String participant) { + return false; + } + + /** + * Participants join a leader election group by calling the following API. + * The Leader Election client maintains and elect an active leader from the participant pool. + * + * @param leaderPath The path for leader election. + * @param participant The participant name to join pool. + * @param userInfo Any additional information to associate with this participant. + * @return boolean indicating if the operation is succeeded. + */ + public boolean joinLeaderElectionParticipantPool(String leaderPath, String participant, + Object userInfo) { + return false; + } + + /** + * Any participant may exit the exitLeaderElectionParticipantPool by calling the API. + * If the participant is not the current leader, it leaves the pool and won't participant future + * leader election process. + * If the participant is the current leader, it leaves the pool and a new leader will be elected + * if there are other participants in the pool. + * Throws exception if the participant is not in the pool. + * + * @param leaderPath The path for leader election. + * @param participant The participant name to exit pool + * @return boolean indicating if the operation is succeeded. + * + * @throws RuntimeException If the participant did not join participant pool via this client. // TODO: define exp type + */ + public boolean exitLeaderElectionParticipantPool(String leaderPath, String participant) { + return false; + } + + /** + * Releases leadership for participant. + * + * @param leaderPath The path for leader election. + * @param participant The participant to release leadership. + * + * @throws RuntimeException if the leadership is not owned by this participant, or if the + * participant did not join participant pool via this client. // TODO: define exp type + */ + public void relinquishLeader(String leaderPath, String participant) { Review Comment: does this mean anyone can call this and release leader -- This is an automated message from the Apache Git Service. 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