org.apache.flink.runtime.leaderelection.LeaderElectionService Maven / Gradle / Ivy
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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,
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* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.flink.runtime.leaderelection;
import javax.annotation.Nonnull;
import java.util.UUID;
/**
* Interface for a service which allows to elect a leader among a group of contenders.
*
* Prior to using this service, it has to be started calling the start method. The start method
* takes the contender as a parameter. If there are multiple contenders, then each contender has
* to instantiate its own leader election service.
*
* Once a contender has been granted leadership he has to confirm the received leader session ID
* by calling the method confirmLeaderSessionID. This will notify the leader election service, that
* the contender has received the new leader session ID and that it can now be published for
* leader retrieval services.
*/
public interface LeaderElectionService {
/**
* Starts the leader election service. This method can only be called once.
*
* @param contender LeaderContender which applies for the leadership
* @throws Exception
*/
void start(LeaderContender contender) throws Exception;
/**
* Stops the leader election service.
* @throws Exception
*/
void stop() throws Exception;
/**
* Confirms that the new leader session ID has been successfully received by the new leader.
* This method is usually called by the newly appointed {@link LeaderContender}.
*
* The rational behind this method is to establish an order between setting the new leader
* session ID in the {@link LeaderContender} and publishing the new leader session ID to the
* leader retrieval services.
*
* @param leaderSessionID The new leader session ID
*/
void confirmLeaderSessionID(UUID leaderSessionID);
/**
* Returns true if the {@link LeaderContender} with which the service has been started owns
* currently the leadership under the given leader session id.
*
* @param leaderSessionId identifying the current leader
*
* @return true if the associated {@link LeaderContender} is the leader, otherwise false
*/
boolean hasLeadership(@Nonnull UUID leaderSessionId);
}