org.apache.flink.runtime.leaderelection

Class DefaultLeaderElectionService

java.lang.Object

org.apache.flink.runtime.leaderelection.DefaultLeaderElectionService

All Implemented Interfaces:

LeaderElectionEventHandler, LeaderElectionService

public class DefaultLeaderElectionService
extends Object
implements LeaderElectionService, LeaderElectionEventHandler

Default implementation for leader election service. Composed with different LeaderElectionDriver, we could perform a leader election for the contender, and then persist the leader information to various storage.

Constructor Summary

Constructors

Constructor and Description
DefaultLeaderElectionService(LeaderElectionDriverFactory leaderElectionDriverFactory)

Method Summary

Modifier and Type	Method and Description
void	confirmLeadership(UUID leaderSessionID, String leaderAddress) Confirms that the LeaderContender has accepted the leadership identified by the given leader session id.
UUID	getLeaderSessionID() Returns the current leader session ID or null, if the contender is not the leader.
boolean	hasLeadership(UUID leaderSessionId) Returns true if the LeaderContender with which the service has been started owns currently the leadership under the given leader session id.
void	onGrantLeadership(UUID newLeaderSessionId) Called by specific LeaderElectionDriver when the leadership is granted.
void	onLeaderInformationChange(LeaderInformation leaderInformation) Called by specific LeaderElectionDriver when the leader information is changed.
void	onRevokeLeadership() Called by specific LeaderElectionDriver when the leadership is revoked.
void	start(LeaderContender contender) Starts the leader election service.
void	stop() Stops the leader election service.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DefaultLeaderElectionService

public DefaultLeaderElectionService(LeaderElectionDriverFactory leaderElectionDriverFactory)

Method Detail

start

public final void start(LeaderContender contender)
                 throws Exception

Description copied from interface: LeaderElectionService

Starts the leader election service. This method can only be called once.

Specified by:

start in interface LeaderElectionService

Parameters:

contender - LeaderContender which applies for the leadership

Throws:

Exception

stop

public final void stop()
                throws Exception

Description copied from interface: LeaderElectionService

Stops the leader election service.

Specified by:

stop in interface LeaderElectionService

Throws:

Exception

confirmLeadership

public void confirmLeadership(UUID leaderSessionID,
                              String leaderAddress)

Description copied from interface: LeaderElectionService

Confirms that the LeaderContender has accepted the leadership identified by the given leader session id. It also publishes the leader address under which the leader is reachable.

The rational behind this method is to establish an order between setting the new leader session ID in the LeaderContender and publishing the new leader session ID as well as the leader address to the leader retrieval services.

Specified by:

confirmLeadership in interface LeaderElectionService

Parameters:

leaderSessionID - The new leader session ID

leaderAddress - The address of the new leader

hasLeadership

public boolean hasLeadership(@Nonnull
                             UUID leaderSessionId)

Description copied from interface: LeaderElectionService

Returns true if the LeaderContender with which the service has been started owns currently the leadership under the given leader session id.

Specified by:

hasLeadership in interface LeaderElectionService

Parameters:

leaderSessionId - identifying the current leader

Returns:

true if the associated LeaderContender is the leader, otherwise false

getLeaderSessionID

@VisibleForTesting
 @Nullable
public UUID getLeaderSessionID()

Returns the current leader session ID or null, if the contender is not the leader.

Returns:

The last leader session ID or null, if the contender is not the leader

onGrantLeadership

public void onGrantLeadership(UUID newLeaderSessionId)

Description copied from interface: LeaderElectionEventHandler

Called by specific LeaderElectionDriver when the leadership is granted.

Specified by:

onGrantLeadership in interface LeaderElectionEventHandler

Parameters:

newLeaderSessionId - the valid leader session id

onRevokeLeadership

public void onRevokeLeadership()

Description copied from interface: LeaderElectionEventHandler

Called by specific LeaderElectionDriver when the leadership is revoked.

Specified by:

onRevokeLeadership in interface LeaderElectionEventHandler

onLeaderInformationChange

public void onLeaderInformationChange(LeaderInformation leaderInformation)

Description copied from interface: LeaderElectionEventHandler

Called by specific LeaderElectionDriver when the leader information is changed. Then the LeaderElectionService could write the leader information again if necessary. This method should only be called when LeaderElectionDriver.hasLeadership() is true. Duplicated leader change events could happen, so the implementation should check whether the passed leader information is really different with internal confirmed leader information.

Specified by:

onLeaderInformationChange in interface LeaderElectionEventHandler

Parameters:

leaderInformation - leader information which contains leader session id and leader address.