DruidLeaderSelector (druid-server 29.0.1 API)

All Known Implementing Classes:

CuratorDruidLeaderSelector
```
public interface DruidLeaderSelector
```
Interface for supporting Overlord and Coordinator Leader Elections in TaskMaster and DruidCoordinator which expect appropriate implementation available in guice annotated with @IndexingService and @Coordinator respectively. Usage is as follows: On lifecycle start: druidLeaderSelector.registerListener(myListener); On lifecycle stop: druidLeaderSelector.unregisterListener();

Nested Class Summary

Nested Classes
Modifier and Type Interface Description

static interface DruidLeaderSelector.Listener

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`String`	`getCurrentLeader()`	Get ID of current Leader.
`boolean`	`isLeader()`	Returns true if this node is elected leader from underlying system's point of view.
`int`	`localTerm()`	Implementation would increment it everytime it becomes leader.
`void`	`registerListener(DruidLeaderSelector.Listener listener)`	Register the listener for watching leadership notifications.
`void`	`unregisterListener()`	Unregisters the listener.

- Method Detail
  - getCurrentLeader
```
@Nullable
String getCurrentLeader()
```
    Get ID of current Leader. Returns NULL if it can't find the leader. Note that it is possible for leadership to change right after this call returns, so caller would get wrong leader. This is expected to work even if a listener is not registered.
  - isLeader
```
boolean isLeader()
```
    Returns true if this node is elected leader from underlying system's point of view. For example if curator is used to implement this then true would be returned when curator believes this node to be the leader. Note that it is possible for leadership to change right after this call returns, so caller would get wrong status.
  - localTerm
```
int localTerm()
```
    Implementation would increment it everytime it becomes leader. This allows users to start a long running task when they become leader and be able to intermittently check that they are still leader from same term when they started. DruidCoordinator class uses it to do intermittent checks and stop the activity as needed.
  - registerListener
```
void registerListener(DruidLeaderSelector.Listener listener)
```
    Register the listener for watching leadership notifications. It should only be called once.
  - unregisterListener
```
void unregisterListener()
```
    Unregisters the listener.