LeadershipService (ONOS Java API (2.5.0))

All Superinterfaces:

ListenerService<LeadershipEvent,LeadershipEventListener>
```
public interface LeadershipService
extends ListenerService<LeadershipEvent,LeadershipEventListener>
```
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.
When a node gets elected as a leader for a topic, all nodes receive notifications indicating a change in leadership.

Method Summary

All Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method	Description
`default List<NodeId>`	`getCandidates(String topic)`	Returns the candidate nodes for a given topic.
`default NodeId`	`getLeader(String topic)`	Returns the `node identifier` that is the current leader for a topic.
`Leadership`	`getLeadership(String topic)`	Returns the current `leadership` for a topic.
`Set<String>`	`ownedTopics(NodeId nodeId)`	Returns the set of topics owned by the specified `node`.
`Leadership`	`runForLeadership(String topic)`	Enters a leadership contest.
`void`	`withdraw(String topic)`	Withdraws from a leadership contest.

Methods inherited from interface org.onosproject.event.ListenerService
addListener, removeListener

- Method Detail
  - getLeader
```
default NodeId getLeader(String topic)
```
    Returns the node identifier that is the current leader for a topic.
    
    Parameters:
    
    topic - leadership topic
    
    Returns:
    
    node identifier of the current leader; null if there is no leader for the topic
  - getLeadership
```
Leadership getLeadership(String topic)
```
    Returns the current leadership for a topic.
    
    Parameters:
    
    topic - leadership topic
    
    Returns:
    
    leadership or null if no such topic exists
  - ownedTopics
```
Set<String> ownedTopics(NodeId nodeId)
```
    Returns the set of topics owned by the specified node.
    
    Parameters:
    
    nodeId - node identifier.
    
    Returns:
    
    set of topics for which this node is the current leader.
  - runForLeadership
```
Leadership runForLeadership(String topic)
```
    Enters a leadership contest.
    
    Parameters:
    
    topic - leadership topic
    
    Returns:
    
    Leadership future
  - withdraw
```
void withdraw(String topic)
```
    Withdraws from a leadership contest.
    
    Parameters:
    
    topic - leadership topic
  - getCandidates
```
default List<NodeId> getCandidates(String topic)
```
    Returns the candidate nodes for a given topic.
    
    Parameters:
    
    topic - leadership topic
    
    Returns:
    
    A lists of nodeIds, which may be empty.