/**
* Starts the Listener so it's actively listening for election results and broadcasts of
* replication group changes.
*
* <p>The Monitor must have been previously registered with the replication group via the <code>
* register()</code> method so that other nodes in the group are aware of it and can keep it
* current. If the monitor has not been registered, it will not be updated, that is, its listener
* will not be invoked. The registration needs to be done exactly once.
*
* <p>Once the registration has been completed, the Monitor can start listening even when none of
* the other nodes in the group are available. It will be contacted automatically by the other
* nodes when they come up and hold a successful election.
*
* <p>Invoking <code>startListener</code> results in a synchronous callback to the application via
* the {@link MonitorChangeListener#notify(NewMasterEvent)} method, if there is a current Master.
* If there is no Master at this time then the callback takes place asynchronously, after the
* method returns, when a Master is eventually elected.
*
* @param newListener the listener used to monitor events of interest.
* @throws EnvironmentFailureException if an unexpected, internal or environment-wide failure
* occurs.
* @throws IOException if the monitor socket could not be set up
* @throws IllegalArgumentException if an invalid parameter is specified.
* @throws IllegalStateException if the monitor has been shutdown, or a listener has already been
* established.
*/
public void startListener(MonitorChangeListener newListener)
throws DatabaseException, IOException {
if (shutdown.get()) {
throw new IllegalStateException("The monitor has been shutdown");
}
if (newListener == null) {
throw new IllegalArgumentException(
"A MonitorChangeListener must be associated with "
+ " this Monitor when invoking this method");
}
if (this.monitorChangeListener != null) {
throw new IllegalStateException("A Listener has already been established");
}
this.monitorChangeListener = newListener;
serviceDispatcher = new ServiceDispatcher(monitorConfig.getNodeSocketAddress());
serviceDispatcher.start();
Protocol electionProtocol =
new Protocol(
TimebasedProposalGenerator.getParser(),
MasterValue.getParser(),
monitorConfig.getGroupName(),
nameIdPair,
null);
learner = new Learner(electionProtocol, serviceDispatcher, nameIdPair);
serviceDispatcher.register(new MonitorService(this, serviceDispatcher));
masterChangeListener = new MasterChangeListener();
learner.addListener(masterChangeListener);
learner.start();
try {
/* Notify the listener about the current master. */
final ReplicationGroup repGroup = repGroupAdmin.getGroup();
final RepGroupImpl group = RepInternal.getRepGroupImpl(repGroup);
/*
* In the absence of a network failure, the query should result in
* a call to the notify method of MonitorChanegListener.
*/
learner.queryForMaster(group.getLearnerSockets());
/* Notify JoinGroupEvents for those current active nodes. */
notifyJoinGroupEventsForActiveNodes(repGroup);
} catch (UnknownMasterException ume) {
/* The Listener will be informed when a Master is elected. */
LoggerUtils.logMsg(logger, formatter, Level.INFO, "No current master.");
}
}
/** Implements the Listener protocol. */
@SuppressWarnings("unused")
public void notify(Proposal proposal, Value value) {
/* We have a winning new proposal, is it truly different? */
if (value.equals(currentValue)) {
return;
}
currentValue = (MasterValue) value;
try {
String currentMasterName = currentValue.getNodeName();
LoggerUtils.logMsg(
logger, formatter, Level.INFO, "Monitor notified of new Master: " + currentMasterName);
if (monitorChangeListener == null) {
/* No interest */
return;
}
monitorChangeListener.notify(new NewMasterEvent(currentValue));
} catch (Exception e) {
LoggerUtils.logMsg(
logger,
formatter,
Level.SEVERE,
"Monitor change event processing exception: " + e.getMessage());
}
}