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/*
* Copyright 2014-2015 Open Networking Laboratory
*
* Licensed 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.onosproject.cluster;
import org.onosproject.event.ListenerService;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.CompletableFuture;
/**
* Service for leader election.
* Leadership contests are organized around topics. A instance can join the
* leadership race for a topic or withdraw from a race it has previously joined.
* Listeners can be added to receive notifications asynchronously for various
* leadership contests.
*/
public interface LeadershipService
extends ListenerService<LeadershipEvent, LeadershipEventListener> {
/**
* Returns the current leader for the topic.
*
* @param path topic
* @return nodeId of the leader, null if so such topic exists.
*/
NodeId getLeader(String path);
/**
* Returns the current leadership info for the topic.
*
* @param path topic
* @return leadership info or null if so such topic exists.
*/
Leadership getLeadership(String path);
/**
* Returns the set of topics owned by the specified node.
*
* @param nodeId node Id.
* @return set of topics for which this node is the current leader.
*/
Set<String> ownedTopics(NodeId nodeId);
/**
* Joins the leadership contest.
*
* @param path topic for which this controller node wishes to be a leader
* @return {@code Leadership} future
*/
CompletableFuture<Leadership> runForLeadership(String path);
/**
* Withdraws from a leadership contest.
*
* @param path topic for which this controller node no longer wishes to be a leader
* @return future that is successfully completed when withdraw is done
*/
CompletableFuture<Void> withdraw(String path);
/**
* If the local nodeId is the leader for specified topic, this method causes it to
* step down temporarily from leadership.
* <p>
* The node will continue to be in contention for leadership and can
* potentially become the leader again if and when it becomes the highest
* priority candidate
* <p>
* If the local nodeId is not the leader, this method will make no changes and
* simply return false.
*
* @param path topic for which this controller node should give up leadership
* @return true if this node stepped down from leadership, false otherwise
*/
boolean stepdown(String path);
/**
* Moves the specified nodeId to the top of the candidates list for the topic.
* <p>
* If the node is not a candidate for this topic, this method will be a noop.
*
* @param path leadership topic
* @param nodeId nodeId to make the top candidate
* @return true if nodeId is now the top candidate, false otherwise
*/
boolean makeTopCandidate(String path, NodeId nodeId);
/**
* Returns the current leader board.
*
* @return mapping from topic to leadership info.
*/
Map<String, Leadership> getLeaderBoard();
/**
* Returns the candidates for all known topics.
*
* @return A mapping from topics to corresponding list of candidates.
*/
Map<String, List<NodeId>> getCandidates();
/**
* Returns the candidates for a given topic.
*
* @param path topic
* @return A lists of NodeIds, which may be empty.
*/
List<NodeId> getCandidates(String path);
}
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