com.sleepycat.je.rep.elections

Class Learner

java.lang.Object

java.lang.Thread

com.sleepycat.je.utilint.StoppableThread

com.sleepycat.je.rep.elections.ElectionAgentThread

com.sleepycat.je.rep.elections.Learner

All Implemented Interfaces:

Runnable

public class Learner
extends ElectionAgentThread

The Learner agent. It runs in its own dedicated thread, listening for messages announcing the results of elections and, in turn, invoking Listeners within the process to propagate the result. It also listens for requests asking for elections results, and provides static methods for requesting those results.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	Learner.Listener

Nested classes/interfaces inherited from class java.lang.Thread

Thread.State, Thread.UncaughtExceptionHandler

Field Summary

Fields

Modifier and Type	Field and Description
static String	SERVICE_NAME

Fields inherited from class com.sleepycat.je.rep.elections.ElectionAgentThread

channelQueue, formatter, logger, protocol

Fields inherited from class com.sleepycat.je.utilint.StoppableThread

envImpl

Fields inherited from class java.lang.Thread

MAX_PRIORITY, MIN_PRIORITY, NORM_PRIORITY

Constructor Summary

Constructors

Constructor and Description
Learner(Protocol protocol, ServiceDispatcher serviceDispatcher) Creates an instance of a Learner which will listen for election results to propagate to local listeners, and for requests asking for election results.
Learner(RepImpl repImpl, Protocol protocol, ServiceDispatcher serviceDispatcher)

Method Summary

Modifier and Type	Method and Description
void	addListener(Learner.Listener listener) Adds a Listener to the existing set of listeners, so that it can be informed of the outcome of election results.
static MasterValue	findMaster(Protocol protocol, Set<InetSocketAddress> learnerSockets, Logger logger, RepImpl repImpl, Formatter formatter) Returns the socket address for the current master, or null if one could not be determined from the available set of learners.
protected Logger	getLogger()
static void	informLearners(Set<InetSocketAddress> learners, Proposer.WinningProposal winningProposal, Protocol protocol, ExecutorService threadPool, Logger logger, RepImpl repImpl, Formatter formatter) A utility method used to broadcast the results of an election to Listeners.
void	processResult(Proposer.Proposal proposal, Protocol.Value value) Processes a result message
void	queryForMaster(Set<InetSocketAddress> learnerSockets) Queries other learners, in parallel, to determine whether they know of an existing master in the group.
void	reinformLearners(Set<InetSocketAddress> learners, ExecutorService threadPool) A method to re-broadcast this Learner's notion of the master.
void	run() The main Learner loop.

Methods inherited from class com.sleepycat.je.rep.elections.ElectionAgentThread

initiateSoftShutdown, shutdown

Methods inherited from class com.sleepycat.je.utilint.StoppableThread

cleanup, getSavedShutdownException, getTotalCpuTime, getTotalUserTime, handleUncaughtException, isShutdown, saveShutdownException, shutdownDone, shutdownThread

Methods inherited from class java.lang.Thread

activeCount, checkAccess, clone, countStackFrames, currentThread, destroy, dumpStack, enumerate, getAllStackTraces, getContextClassLoader, getDefaultUncaughtExceptionHandler, getId, getName, getPriority, getStackTrace, getState, getThreadGroup, getUncaughtExceptionHandler, holdsLock, interrupt, interrupted, isAlive, isDaemon, isInterrupted, join, join, join, resume, setContextClassLoader, setDaemon, setDefaultUncaughtExceptionHandler, setName, setPriority, setUncaughtExceptionHandler, sleep, sleep, start, stop, stop, suspend, toString, yield

Methods inherited from class java.lang.Object

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

Field Detail

SERVICE_NAME

public static final String SERVICE_NAME

See Also:

Constant Field Values

Constructor Detail

Learner

public Learner(Protocol protocol,
               ServiceDispatcher serviceDispatcher)

Creates an instance of a Learner which will listen for election results to propagate to local listeners, and for requests asking for election results.

Note that this constructor does not take a repNode as an argument, so that it can be used as the basis for the standalone Monitor.

Parameters:

protocol - the protocol used for message exchange

serviceDispatcher - the service dispatcher used by the agent

Learner

public Learner(RepImpl repImpl,
               Protocol protocol,
               ServiceDispatcher serviceDispatcher)

Method Detail

addListener

public void addListener(Learner.Listener listener)

Adds a Listener to the existing set of listeners, so that it can be informed of the outcome of election results.

Parameters:

listener - the new listener to be added

processResult

public void processResult(Proposer.Proposal proposal,
                          Protocol.Value value)

Processes a result message

Parameters:

proposal - the winning proposal

value - the winning value

run

public void run()

The main Learner loop. It accepts requests and propagates them to its Listeners, if the proposal isn't out of date.

Specified by:

run in interface Runnable

Overrides:

run in class Thread

queryForMaster

public void queryForMaster(Set<InetSocketAddress> learnerSockets)

Queries other learners, in parallel, to determine whether they know of an existing master in the group. If one is found, the result is processed via processResult(com.sleepycat.je.rep.elections.Proposer.Proposal, com.sleepycat.je.rep.elections.Protocol.Value) as though it were an election result that was sent to the Learner, resulting in the node transitioning to the master or replica state as appropriate.

Note that this node itself is not allowed to become a master as a result of such a query. It must only do so via an election.

Parameters:

learnerSockets - the sockets associated with learners at other nodes. The nodes are queried on these sockets.

findMaster

public static MasterValue findMaster(Protocol protocol,
                                     Set<InetSocketAddress> learnerSockets,
                                     Logger logger,
                                     RepImpl repImpl,
                                     Formatter formatter)
                              throws UnknownMasterException

Returns the socket address for the current master, or null if one could not be determined from the available set of learners. This API is suitable for tools which need to contact the master for a specific service, e.g. to delete a replication node, or to add a monitor. This method could be used in principle to establish other types of nodes as well via a tool, but that is currently done by the handshake process.

Parameters:

protocol - the protocol to be used when determining the master

learnerSockets - the learner to be queried for the master

logger - for log messages

Returns:

the MasterValue identifying the master

Throws:

UnknownMasterException - if no master could be established

reinformLearners

public void reinformLearners(Set<InetSocketAddress> learners,
                             ExecutorService threadPool)

A method to re-broadcast this Learner's notion of the master. This re-broadcast is done primarily to inform an obsolete master that it's no longer the current master. Obsolete master situations arise in network partition scenarios, where a current master is not able to participate in an election, nor is it informed about the results. The re-broadcast is the mechanism for rectifying such a situation. When the obsolete master receives the new results after the network partition has been fixed, it will revert to being a replica.

Parameters:

learners - the learners that must be informed

threadPool - the pool used to dispatch broadcast requests in in parallel

informLearners

public static void informLearners(Set<InetSocketAddress> learners,
                                  Proposer.WinningProposal winningProposal,
                                  Protocol protocol,
                                  ExecutorService threadPool,
                                  Logger logger,
                                  RepImpl repImpl,
                                  Formatter formatter)

A utility method used to broadcast the results of an election to Listeners.

Parameters:

learners - that need to be informed.

winningProposal - the result that needs to be propagated

protocol - to be used for communication

threadPool - used to supply threads for the broadcast

getLogger

protected Logger getLogger()

Overrides:

getLogger in class ElectionAgentThread

Returns:

a logger to use when logging uncaught exceptions.

See Also:

StoppableThread.getLogger()