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io.mats3.matsbrokermonitor.activemq.ActiveMqBrokerStatsQuerierImpl Maven / Gradle / Ivy

package io.mats3.matsbrokermonitor.activemq;

import java.time.Clock;
import java.time.Instant;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Iterator;
import java.util.Optional;
import java.util.OptionalDouble;
import java.util.concurrent.ConcurrentNavigableMap;
import java.util.concurrent.ConcurrentSkipListMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Consumer;

import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.DeliveryMode;
import javax.jms.JMSException;
import javax.jms.MapMessage;
import javax.jms.Message;
import javax.jms.MessageConsumer;
import javax.jms.MessageProducer;
import javax.jms.Queue;
import javax.jms.Session;
import javax.jms.Topic;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;

/**
 * @author Endre Stølsvik 2021-12-20 18:00 - http://stolsvik.com/, [email protected]
 */
public class ActiveMqBrokerStatsQuerierImpl implements ActiveMqBrokerStatsQuerier, Statics {

    private static final Logger log = LoggerFactory.getLogger(ActiveMqBrokerStatsQuerierImpl.class);
    private static final Logger log_update = LoggerFactory.getLogger(ActiveMqBrokerStatsQuerierImpl.class.getName()
            + ".Update");

    private static final String CORRELATION_ID_PREFIX_SCHEDULED = "Scheduled";
    private static final String CORRELATION_ID_PREFIX_FORCED = "Forced";
    private static final String CORRELATION_ID_PARAMETER_FULL_UPDATE = "fullUpdate";
    private static final String CORRELATION_ID_PARAMETER_NODE_ID = "nodeId";

    private String _nodeId = Long.toString(Math.abs(ThreadLocalRandom.current().nextLong()), 36)
            + Long.toString(Math.abs(ThreadLocalRandom.current().nextLong()), 36);

    private final ConnectionFactory _connectionFactory;
    private final Clock _clock;
    private final long _updateIntervalMillis;

    /**
     * 2.5 minutes query interval.
     */
    static ActiveMqBrokerStatsQuerierImpl create(ConnectionFactory connectionFactory) {
        return create(connectionFactory, DEFAULT_UPDATE_INTERVAL_MILLIS);
    }

    /**
     * Using specified query interval, should not be too small, in particular if lots of queues and topics, as each
     * queue and topic gets its own statistics reply message: Less than 30 seconds would be much too often.
     */
    static ActiveMqBrokerStatsQuerierImpl create(ConnectionFactory connectionFactory, long updateIntervalMillis) {
        return new ActiveMqBrokerStatsQuerierImpl(connectionFactory, Clock.systemUTC(), updateIntervalMillis);
    }

    private ActiveMqBrokerStatsQuerierImpl(ConnectionFactory connectionFactory, Clock clock,
            long updateIntervalMillis) {
        _connectionFactory = connectionFactory;
        _clock = clock;
        _updateIntervalMillis = updateIntervalMillis;
    }

    private enum RunStatus {
        NOT_STARTED,

        RUNNING,

        CLOSED
    }

    private String _matsDestinationPrefix = "mats.";

    private final Deque _waitObject_And_ForceUpdateOutstandingCorrelationIds = new ArrayDeque<>();

    // RunStatus: NOT_STARTED -> RUNNING -> CLOSED. Not restartable.
    private volatile RunStatus _runStatus = RunStatus.NOT_STARTED;

    private volatile Thread _sendStatsRequestMessages_Thread;
    private volatile Thread _receiveDestinationsStatsReplyMessages_Thread;
    private volatile Connection _receiveDestinationsStatsReplyMessages_Connection;

    private volatile long _lastFullUpdatePropagatedMillis;

    private volatile long _lastStatsUpdateMessageReceived = System.currentTimeMillis();

    // Reset in request thread, used in receive thread.
    private final AtomicInteger _countOfDestinationsReceivedAfterRequest = new AtomicInteger();

    // Only used from receive thread.
    private int _countOfDestinationsReceivedSinceLastBatch;
    private volatile long _nanosAtStart_RequestQuery = 0;

    private volatile BrokerStatsDto _currentBrokerStatsDto;
    private final ConcurrentNavigableMap _currentDestinationStatsDtos = new ConcurrentSkipListMap<>();

    private final CopyOnWriteArrayList> _listeners = new CopyOnWriteArrayList<>();

    @Override
    public void setNodeId(String nodeId) {
        _nodeId = nodeId;
    }

    public void start() {
        if (_runStatus == RunStatus.CLOSED) {
            throw new IllegalStateException("Asked to start, but runStatus==CLOSED, so have already been closed.");
        }
        if (_runStatus == RunStatus.RUNNING) {
            log.info("Asked to start, but already running. Ignoring.");
            return;
        }
        // First set _runStatus to RUNNING, so threads will be happy
        _runStatus = RunStatus.RUNNING;
        log.info("Starting ActiveMQ Broker statistics querier.");
        String id = "(Querier@" + Integer.toHexString(System.identityHashCode(this)) + ")";
        _sendStatsRequestMessages_Thread = new Thread(this::sendStatsRequestMessages,
                "MatsBrokerMonitor.ActiveMQ: Send Statistics request messages " + id);
        _receiveDestinationsStatsReplyMessages_Thread = new Thread(this::receiveStatisticsReplyMessagesRunnable,
                "MatsBrokerMonitor.ActiveMQ: Receive&Process Statistics reply messages " + id);

        // :: First start reply consumer
        _receiveDestinationsStatsReplyMessages_Thread.start();
        // .. then starting requester (it will chill a small tad after getting connection before doing first request)
        _sendStatsRequestMessages_Thread.start();
    }

    @Override
    public void close() {
        if (_runStatus == RunStatus.CLOSED) {
            log.warn("Asked to close, but runStatus==CLOSED, so must already have been stopped. Ignoring.");
            return;
        }
        if (_runStatus == RunStatus.NOT_STARTED) {
            log.warn("Asked to close, but runStatus==NOT_STARTED, so have never been started."
                    + " Setting directly to CLOSED.");
            _runStatus = RunStatus.CLOSED;
            return;
        }

        // First set _runStatus to CLOSED, so that any loops and checks will exit.
        _runStatus = RunStatus.CLOSED;
        log.info("Asked to close. Set runStatus to CLOSED, closing Connections and interrupting threads.");

        // Notify the request sender - it'll close the Connection on its way out.
        synchronized (_waitObject_And_ForceUpdateOutstandingCorrelationIds) {
            _waitObject_And_ForceUpdateOutstandingCorrelationIds.notifyAll();
        }

        // Closing Connections for the receiver - the thread will wake up from 'con.receive()'.
        closeConnectionIfNonNullIgnoreException(_receiveDestinationsStatsReplyMessages_Connection);

        // Check that both threads exit
        try {
            _sendStatsRequestMessages_Thread.join(TIMEOUT_MILLIS_GRACEFUL_THREAD_SHUTDOWN);
            _receiveDestinationsStatsReplyMessages_Thread.join(TIMEOUT_MILLIS_GRACEFUL_THREAD_SHUTDOWN);
        }
        catch (InterruptedException e) {
            /* ignore */
        }
        // .. interrupt the request sender if the above didn't work.
        interruptThread(_sendStatsRequestMessages_Thread);
        // .. interrupt the receiver too if they haven't gotten out.
        interruptThread(_receiveDestinationsStatsReplyMessages_Thread);
        // Null out Threads
        _sendStatsRequestMessages_Thread = null;
        _receiveDestinationsStatsReplyMessages_Thread = null;
    }

    @Override
    public void setMatsDestinationPrefix(String matsDestinationPrefix) {
        if (_runStatus != RunStatus.NOT_STARTED) {
            throw new IllegalStateException("Tried setting matsDestinationPrefix, but runStatus != NOT_STARTED.");
        }
        _matsDestinationPrefix = matsDestinationPrefix;
    }

    private static void closeConnectionIfNonNullIgnoreException(Connection connection) {
        if (connection == null) {
            return;
        }
        try {
            connection.close();
        }
        catch (JMSException e) {
            log.warn("Got [" + e.getClass().getSimpleName() + "] when trying to close Connection [" + connection
                    + "], ignoring.");
        }
    }

    private void interruptThread(Thread thread) {
        if (thread != null) {
            thread.interrupt();
        }
    }

    @Override
    public void registerListener(Consumer listener) {
        _listeners.add(listener);
    }

    private String constructCorrelationIdToSend(boolean forced, boolean fullUpdate, String correlationId) {
        return (forced ? CORRELATION_ID_PREFIX_FORCED : CORRELATION_ID_PREFIX_SCHEDULED)
                + ":" + CORRELATION_ID_PARAMETER_FULL_UPDATE + "." + fullUpdate
                + ":" + CORRELATION_ID_PARAMETER_NODE_ID + "." + _nodeId
                + ":" + correlationId;
    }

    private static CorrSplit splitCorrelation(String sentCorrelationid) {
        int firstColon = sentCorrelationid.indexOf(':');
        String prefix = sentCorrelationid.substring(0, firstColon);
        int secondColon = sentCorrelationid.indexOf(':', firstColon + 1);
        String full = sentCorrelationid.substring(firstColon + 1, secondColon);
        int thirdColon = sentCorrelationid.indexOf(':', secondColon + 1);
        String node = sentCorrelationid.substring(secondColon + 1, thirdColon);
        // The actual CorrelationId is the rest of the String
        String correlationId = sentCorrelationid.substring(thirdColon + 1);

        boolean forced = CORRELATION_ID_PREFIX_FORCED.equals(prefix);
        boolean fullUpdate = full.contains("true");
        String nodeId = node.substring(CORRELATION_ID_PARAMETER_NODE_ID.length() + 1);

        return new CorrSplit(forced, fullUpdate, nodeId, correlationId);
    }

    private static class CorrSplit {
        final boolean forced;
        final boolean fullUpdate;
        final String nodeId;
        final String correlationId;

        public CorrSplit(boolean forced, boolean fullUpdate, String nodeId, String correlationId) {
            this.forced = forced;
            this.fullUpdate = fullUpdate;
            this.nodeId = nodeId;
            this.correlationId = correlationId;
        }
    }

    @Override
    public void forceUpdate(String correlationId, boolean fullUpdate) {
        synchronized (_waitObject_And_ForceUpdateOutstandingCorrelationIds) {
            _waitObject_And_ForceUpdateOutstandingCorrelationIds.add(constructCorrelationIdToSend(true, fullUpdate,
                    correlationId));
            // ?: Are there WAY too many outstanding correlation Ids?
            if (_waitObject_And_ForceUpdateOutstandingCorrelationIds
                    .size() > MAX_NUMBER_OF_OUTSTANDING_CORRELATION_IDS) {
                // -> Yes, so then we're actually screwed - there are obviously no response from the broker
                log.error("We have " + MAX_NUMBER_OF_OUTSTANDING_CORRELATION_IDS + " outstanding forced updates with"
                        + " correlationIds, which implies that the broker does not respond. We'll just ditch them all"
                        + " to prevent OOME; you need to figure out the problem: Probably the"
                        + " Statistics[Broker]Plugin is not installed on the ActiveMQ server.");
                _waitObject_And_ForceUpdateOutstandingCorrelationIds.clear();
            }
            _waitObject_And_ForceUpdateOutstandingCorrelationIds.notifyAll();
        }
    }

    private static class ActiveMqBrokerStatsEventImpl implements ActiveMqBrokerStatsEvent {
        private final String _correlationId;
        private final boolean _fullUpdate;
        private final boolean _statsEventOriginatedOnThisNode;
        private final String _originatingNodeId;
        private final double _requestReplyLatencyMillis;

        public ActiveMqBrokerStatsEventImpl(String correlationId, boolean fullUpdate,
                boolean statsEventOriginatedOnThisNode,
                String originatingNodeId, double requestReplyLatencyMillis) {
            _correlationId = correlationId;
            _fullUpdate = fullUpdate;
            _statsEventOriginatedOnThisNode = statsEventOriginatedOnThisNode;
            _originatingNodeId = originatingNodeId;
            _requestReplyLatencyMillis = requestReplyLatencyMillis;
        }

        /**
         * Only present if forced update.
         */
        @Override
        public Optional getCorrelationId() {
            return Optional.ofNullable(_correlationId);
        }

        @Override
        public boolean isFullUpdate() {
            return _fullUpdate;
        }

        @Override
        public boolean isStatsEventOriginatedOnThisNode() {
            return _statsEventOriginatedOnThisNode;
        }

        @Override
        public Optional getOriginatingNodeId() {
            return Optional.ofNullable(_originatingNodeId);
        }

        @Override
        public OptionalDouble getStatsRequestReplyLatencyMillis() {
            return _requestReplyLatencyMillis >= 0
                    ? OptionalDouble.of(_requestReplyLatencyMillis)
                    : OptionalDouble.empty();
        }
    }

    public Optional getCurrentBrokerStatsDto() {
        return Optional.ofNullable(_currentBrokerStatsDto);
    }

    public ConcurrentNavigableMap getCurrentDestinationStatsDtos() {
        return _currentDestinationStatsDtos;
    }

    // ===== IMPLEMENTATION =====

    private void sendStatsRequestMessages() {
        Connection sendRequestMessages_Connection = null;
        while (_runStatus == RunStatus.RUNNING) {
            try {
                sendRequestMessages_Connection = _connectionFactory.createConnection();
                sendRequestMessages_Connection.start();
                Session session = sendRequestMessages_Connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
                MessageProducer producer = session.createProducer(null);
                // If there are no receiver (StatisticsPlugin not installed), then try to prevent build-up of msgs.
                producer.setTimeToLive(5 * 60 * 1000); // 5 minutes.
                // Just to point out that there is no need to save these messages if they cannot be handled.
                producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);

                Queue requestQueuesQueue_main;
                Topic requestTopicsTopic_main;

                // -> No, this is a bad prefix that cannot utilize the wildcard syntax, so have to ask for every
                // single queue and topic.
                String queryRequestDestination_all = QUERY_REQUEST_DESTINATION_PREFIX + ".>";

                log.info("The matsDestinationPrefix was set to [" + _matsDestinationPrefix + "], but this isn't"
                        + " a proper \"path-style\" prefix (it is not ending with a dot), thus cannot restrict"
                        + " the query to mats-specific destinations, but must query for all destinations by"
                        + " employing [" + queryRequestDestination_all + "]");
                requestQueuesQueue_main = session.createQueue(queryRequestDestination_all);
                requestTopicsTopic_main = session.createTopic(queryRequestDestination_all);

                // :: Create queue for the "zero-termination", sent in a separate request query
                // NOTE: We just ask for a queue which shall not be there, but request the "zero termination".
                Queue requestQueuesQueue_zeroQueuesMatchWithNullTermination = session.createQueue(
                        QUERY_REQUEST_DESTINATION_PREFIX + ".No_Match_Whatsoever_"
                                + Long.toString(Math.abs(ThreadLocalRandom.current().nextLong()), 36));

                // Request BrokerStats topic
                Topic requestBrokerTopic = session.createTopic(QUERY_REQUEST_BROKER);
                // Reply topic for all statistics messages (this thread)
                Topic replyStatisticsTopic = session.createTopic(QUERY_REPLY_STATISTICS_TOPIC);

                // Chill a small tad before sending first request, so that receivers hopefully have started.
                // Notice: It isn't particularly bad if they haven't, they'll just miss the first request/reply.
                chill((long) (CHILL_MILLIS_BEFORE_FIRST_STATS_REQUEST
                        * (1 + ThreadLocalRandom.current().nextDouble())));

                String correlationIdToSend = null;

                while (_runStatus == RunStatus.RUNNING) {
                    // :: Request stats for Broker
                    Message requestBrokerMsg = session.createMessage();
                    requestBrokerMsg.setJMSReplyTo(replyStatisticsTopic);
                    producer.send(requestBrokerTopic, requestBrokerMsg);

                    // ::: Destinations
                    // (Notice: Directing replyTo for both Queues and Topics reply to same receiver.)
                    // :: Request stats for Queues
                    Message requestQueuesMsg = session.createMessage();
                    set_includeFirstMessageTimestamp(requestQueuesMsg);
                    requestQueuesMsg.setJMSReplyTo(replyStatisticsTopic);

                    // :: Request stats for Topics
                    Message requestTopicsMsg = session.createMessage();
                    set_includeFirstMessageTimestamp(requestTopicsMsg);
                    requestTopicsMsg.setJMSReplyTo(replyStatisticsTopic);

                    // :: Send destination stats messages
                    // Clear the count of destinations received since this request (we start counting from now)
                    _countOfDestinationsReceivedAfterRequest.set(0);
                    // We start timing from now
                    _nanosAtStart_RequestQuery = System.nanoTime();
                    producer.send(requestQueuesQueue_main, requestQueuesMsg);
                    producer.send(requestTopicsTopic_main, requestTopicsMsg);

                    // :: Send the null-termination query (query w/o any destination replies, only the null-terminator)

                    // Do we currently have a specific correlationId?
                    if (correlationIdToSend == null) {
                        // -> No specific correlation Id, so make a "normal" Scheduled correlationId.
                        // Should we do a full-update, since long time since last full update?
                        boolean timeBasedFullUpdate = (System.currentTimeMillis()
                                - _lastFullUpdatePropagatedMillis) > FULL_UPDATE_INTERVAL;
                        // A random correlationId. Not really used.
                        String random = Long.toString(ThreadLocalRandom.current().nextLong(), 36);
                        correlationIdToSend = constructCorrelationIdToSend(false, timeBasedFullUpdate, random);
                    }

                    // .. construct the null-termination message
                    Message requestNullTermination = session.createMessage();
                    requestNullTermination.setJMSReplyTo(replyStatisticsTopic);
                    // .. set the special property which directs the StatisticsPlugin to "empty terminate" the replies.
                    requestNullTermination.setBooleanProperty(QUERY_REQUEST_DENOTE_END_LIST, true);
                    requestNullTermination.setJMSCorrelationID(correlationIdToSend);
                    producer.send(requestQueuesQueue_zeroQueuesMatchWithNullTermination, requestNullTermination);

                    // We've done this job, clear out correlationId
                    correlationIdToSend = null;

                    // :: Chill and loop
                    synchronized (_waitObject_And_ForceUpdateOutstandingCorrelationIds) {
                        // :: Go into wait: Either we're waking by interval, or by forced update
                        // Loop till we decide that we should do request.
                        while (_runStatus == RunStatus.RUNNING) {
                            // ?: Do we have a forced update waiting?
                            if (!_waitObject_And_ForceUpdateOutstandingCorrelationIds.isEmpty()) {
                                // -> Yes, so pop the force update correlationId before looping.
                                correlationIdToSend = _waitObject_And_ForceUpdateOutstandingCorrelationIds.remove();
                                // Break out of wait-loop
                                break;
                            }
                            // E-> No forced update, so calculate how long to wait
                            // 10% randomness, 5% to both sides
                            long randomRange = (long) Math.max(150, _updateIntervalMillis * .1d);
                            long randomness = Math.round(ThreadLocalRandom.current().nextDouble() * randomRange);
                            long currentWait = Math.max(1, _updateIntervalMillis - (randomRange / 2) + randomness);

                            // Do wait.
                            _waitObject_And_ForceUpdateOutstandingCorrelationIds.wait(currentWait);

                            // ?: Not running anymore?
                            if (_runStatus != RunStatus.RUNNING) {
                                // -> Break out of wait loop (and then all the way out, due to loop conditionals.).
                                break;
                            }
                            // ?: Forced update waiting?
                            if (!_waitObject_And_ForceUpdateOutstandingCorrelationIds.isEmpty()) {
                                // -> Loop (waitloop) to get correlationId (and then break).
                                continue;
                            }

                            // :: Check if we actually should do the request, or if the other node has already done it.

                            // ?: Is the last received stats message older than 75% of our interval?
                            if (_lastStatsUpdateMessageReceived < (System.currentTimeMillis()
                                    - (_updateIntervalMillis * 0.75d))) {
                                // -> Yes, the message is overdue enough, so let's do the request
                                log.debug("Last received StatsUpdateMessage is too old (I am probably first of the"
                                        + " nodes, or the only node); I will do the request");
                                // Break out of wait-loop
                                break;
                            }
                            else {
                                log.debug("Last received update is pretty fresh (probably gotten from another node);"
                                        + " I will NOT do the request.");
                            }
                        }
                    }
                }
            }
            catch (Throwable t) {
                // ?: Exiting?
                if (_runStatus != RunStatus.RUNNING) {
                    // -> Yes, exiting, so get out.
                    break;
                }
                log.warn("Got a [" + t.getClass().getSimpleName() + "] in the query-loop."
                        + " Attempting to close JMS Connection if gotten, then chill-waiting, then trying again.", t);
                closeConnectionIfNonNullIgnoreException(sendRequestMessages_Connection);
                chill(CHILL_MILLIS_WAIT_AFTER_THROWABLE_IN_RECEIVE_LOOPS);
            }
        }
        // To exit, we're signalled via interrupt - it is our job to close Connection (it is a local variable)
        closeConnectionIfNonNullIgnoreException(sendRequestMessages_Connection);
        log.info("Got asked to exit, and that we do!");
    }

    private void set_includeFirstMessageTimestamp(Message msg) throws JMSException {
        msg.setBooleanProperty(QUERY_REQUEST_DESTINATION_INCLUDE_FIRST_MESSAGE_TIMESTAMP, true);
    }

    // Only used within receiveStatisticsReplyMessagesRunnable-thread.

    @SuppressWarnings("unchecked")
    private void receiveStatisticsReplyMessagesRunnable() {
        OUTERLOOP: while (_runStatus == RunStatus.RUNNING) {
            try {
                _receiveDestinationsStatsReplyMessages_Connection = _connectionFactory.createConnection();
                _receiveDestinationsStatsReplyMessages_Connection.start();
                Session session = _receiveDestinationsStatsReplyMessages_Connection.createSession(false,
                        Session.AUTO_ACKNOWLEDGE);
                Topic replyTopic = session.createTopic(QUERY_REPLY_STATISTICS_TOPIC);
                MessageConsumer consumer = session.createConsumer(replyTopic);

                long nanosAtEnd_lastMessageReceived = 0;
                while (_runStatus == RunStatus.RUNNING) {

                    // Note: The logic here is that we'll get a bunch of statistics reply messages, ended by either
                    // an explicit "empty terminator", or by timing out. This first, timed receive is for the "bunch",
                    // while the later, indefinite receive is for waiting for the next batch.

                    // Since I do not feel utterly confident about the ordering of the messages vs. the multiple
                    // requests and the last "empty terminator", we should also handle that a bunch is split into
                    // two parts: Some replies, the empty terminator, and the rest of the replies. This is not handled
                    // /good/, but we will at least receive the stats messages. However, the fired event will be too
                    // early. This will definitely be a "eventually consistent" scenario - so lets hope the ordering
                    // holds, in which case we have a very good consistency wrt. when sending the update event.

                    // The net effect here is that we will receive stats updates for everything we want, but the
                    // ordering and clean division into "sets" based on the requests being sent cannot be totally
                    // guaranteed - both due to mentioned ordering, but also the fact that there should be multiple
                    // nodes running this (so that we can get interleaving of requests), and that downstream can at
                    // any point request a forced update request, which might come right after a scheduled update req.

                    // However, since we do stack everything we get up into a persistent memory map on this side, we
                    // will just get more and more current information. As long as we eventually notify our listeners
                    // (the ActiveMqMatsBrokerMonitor), the downstream will get a good view about the broker state.
                    // (The map is scavenged based on time: If there are old destinations that haven't gotten an update
                    // for a longish time, it is assumed that the destination is gone from the broker).

                    // Go into timed receive (receiving "the rest of the bunch", but handling startup)
                    MapMessage statsMsg = (MapMessage) consumer.receive(
                            TIMEOUT_MILLIS_FOR_LAST_MESSAGE_IN_BATCH_FOR_DESTINATION_STATS);

                    // NOTE: We're using an undocumented feature of ActiveMQ's StatisticsBrokerPlugin whereby if we add
                    // a special marker to the query, the replies will be "empty terminated" by an empty MapMessage.

                    // ?: Check run flag - exit if we're not running anymore.
                    if (_runStatus != RunStatus.RUNNING) {
                        break OUTERLOOP;
                    }

                    // ?: Did we either get a null, or get an "empty" MapMessage?
                    // (Null would be timeout for stats, empty MapMessage would be the "null termination" for stats.)
                    if ((statsMsg == null) || (statsMsg.getObject("brokerName") == null)) {
                        // -> null or empty, but runStatus==RUNNING, so this was a timeout or "terminator".

                        // Now evaluate whether this was the end of a batch of destination stats messages, and if
                        // so, fire the event.
                        evaluateEndOfBatch(statsMsg, nanosAtEnd_lastMessageReceived);

                        // ----- So, either startup, or we've finished a batch of messages:
                        // Go into indefinite receive: Waiting for _next batch_ of messages triggered by _next stats
                        // request_. (Or null message, resulting from outside close due to shutdown)
                        statsMsg = (MapMessage) consumer.receive();
                    }

                    // ----- We've either got a message from the loop, or a new message after a batch.

                    // ?: Was this a null-message, most probably denoting that we're exiting?
                    if (statsMsg == null) {
                        // -> Yes, null message received.
                        log.info("Received null message from consumer.receive(), assuming shutdown.");
                        if (_runStatus != RunStatus.RUNNING) {
                            break OUTERLOOP;
                        }
                        throw new UnexpectedNullMessageReceivedException("Null message received,"
                                + " but runFlag still true?!");
                    }

                    // :: Evaluate whether it is a BrokerStatistics or DestinationStatistics message
                    if (statsMsg.getObject("destinationName") != null) {
                        // -> Destination stats
                        // This was a destination stats message - count it
                        _countOfDestinationsReceivedAfterRequest.incrementAndGet();
                        _countOfDestinationsReceivedSinceLastBatch++;
                        // .. log time we received this destination stats message
                        nanosAtEnd_lastMessageReceived = System.nanoTime();

                        DestinationStatsDto destinationStatsDto = mapMessageToDestinationStatsDto(statsMsg);
                        _currentDestinationStatsDtos.put(destinationStatsDto.destinationName, destinationStatsDto);
                        // Update that we've gotten a stats-message
                        _lastStatsUpdateMessageReceived = System.currentTimeMillis();
                        if (log.isTraceEnabled()) log.trace("Got DestinationStats: " + destinationStatsDto);
                    }
                    else if (statsMsg.getObject("storeUsage") != null) {
                        // -> Broker stats
                        _currentBrokerStatsDto = mapMessageToBrokerStatsDto(statsMsg);
                        // Update that we've gotten a stats-message
                        _lastStatsUpdateMessageReceived = System.currentTimeMillis();
                        if (log.isTraceEnabled()) log.trace("Got BrokerStats: " + _currentBrokerStatsDto);
                    }
                    else {
                        log.info("Got a JMS Message that was neither destination stats nor broker stats."
                                + " This is probably an unexpected 'null termination' which happened because more than"
                                + " one instance of the querier sent stats query at the same time, thus getting two"
                                + " replies concurrently. Should not happen often since we have forced randomness in"
                                + " query interval. If it does happen often, either your interval is too low,"
                                + " you have high load or latency, very many queues - or gimme a call! \n" + statsMsg);
                    }
                }
            }
            catch (Throwable t) {
                // ?: Exiting?
                if (_runStatus != RunStatus.RUNNING) {
                    // -> Yes, exiting, so get out.
                    break;
                }
                log.warn("Got a [" + t.getClass().getSimpleName() + "] in the receive-loop."
                        + " Attempting to close JMS Connection if gotten, then chill-waiting, then trying again.", t);
                closeConnectionIfNonNullIgnoreException(_receiveDestinationsStatsReplyMessages_Connection);
                chill(CHILL_MILLIS_WAIT_AFTER_THROWABLE_IN_RECEIVE_LOOPS);
            }
        }
        // To exit, we're signalled via the JMS Connection being closed; Our job is just to null it on our way out.
        _receiveDestinationsStatsReplyMessages_Connection = null;
        log.info("Got asked to exit, and that we do!");
    }

    private void evaluateEndOfBatch(MapMessage statsMsg, long nanosAtEnd_lastMessageReceived) throws JMSException {
        // :: Extract information from the JMS Message's CorrelationId.
        // ?: Have we gotten (bunch of) stats messages by now?
        if (_countOfDestinationsReceivedSinceLastBatch > 0) {
            // -> We've gotten 1 or more stats messages.

            // We've now (hopefully) received a full set of destination stats.

            // :: Pick out pieces of the raw correlation if we came here based on a final last message.
            // (Does not work if we came here due to timeout, as we don't then have a message.)
            String correlationId = null;
            boolean isFullUpdate = false;
            String originatingNodeId = null;
            boolean requestSameNode = false;
            if (statsMsg != null) {
                String raw = statsMsg.getJMSCorrelationID();
                if (raw != null) {
                    CorrSplit corrSplit = splitCorrelation(raw);
                    // Only use the correlationId if it was supplied via a forceUpdate.
                    correlationId = corrSplit.forced ? corrSplit.correlationId : null;
                    isFullUpdate = corrSplit.fullUpdate;
                    originatingNodeId = corrSplit.nodeId;
                    requestSameNode = _nodeId.equals(originatingNodeId);
                }
            }

            // :: Log the update with metrics.

            MDC.put("mats.mbm.fullUpdate", Boolean.toString(isFullUpdate));
            MDC.put("mats.mbm.requestSameNode", Boolean.toString(requestSameNode));
            if (correlationId != null) {
                MDC.put("mats.mbm.correlationId", correlationId);
            }

            String msg = "#MBM_UPDATE# (Request " + (requestSameNode ? "IS" : "is NOT") + " from this node,"
                    + " this: " + _nodeId + ", originating: " + originatingNodeId + ")"
                    + " We've received a batch of ["
                    + _countOfDestinationsReceivedSinceLastBatch
                    + "] destination stats messages, current number of destinations ["
                    + _currentDestinationStatsDtos.size()
                    + "]";
            if (requestSameNode) {
                long nanosRequestFinalReplyLatency = nanosAtEnd_lastMessageReceived
                        - _nanosAtStart_RequestQuery;
                long nanosBetweenQueryAndNow = System.nanoTime() - _nanosAtStart_RequestQuery;

                long extraLatency = nanosBetweenQueryAndNow - nanosRequestFinalReplyLatency;

                MDC.put("mats.mbm.requestReplyLatencyMillis",
                        Double.toString(ms3(nanosRequestFinalReplyLatency)));
                MDC.put("mats.mbm.extraLatency",
                        Double.toString(ms3(extraLatency)));

                msg += ", request-to-final-reply latency:"
                        + " [" + ms3(nanosRequestFinalReplyLatency) + "] ms"
                        + " - extra latency [" + ms3(extraLatency) + "] ms";
            }
            msg += ". Notifying local listeners.";
            log_update.info(msg);

            MDC.clear();

            /*
             * :: If this is a full update, then note this. We decide whether full update on the request-sending side,
             * and note the last full update on ActiveMq _replies received_ side, so that if the other node did the full
             * update _request_, all nodes will notice and agree on when the last full update was propagated. (The
             * sender will automatically tag request as full-update if > X mins since last)
             */
            if (isFullUpdate) {
                _lastFullUpdatePropagatedMillis = System.currentTimeMillis();
            }

            /*
             * Clean out old destinations by scavenging stats which no longer is getting updates (i.e. not existing
             * anymore).
             *
             * Would have been nice to run this as a full-update when we scavenge some destinations, but that could be
             * messy as we might not be sure the multiple MBM nodes are in sync wrt. "old" destinations. So, we'll just
             * let the next scheduled full update do the job.
             */
            long longAgo = System.currentTimeMillis() - SCAVENGE_OLD_STATS_SECONDS * 1000;
            Iterator currentStatsIterator = _currentDestinationStatsDtos
                    .values().iterator();
            while (currentStatsIterator.hasNext()) {
                DestinationStatsDto stats = currentStatsIterator.next();
                if (stats.statsReceived.toEpochMilli() < longAgo) {
                    log.info("Removing destination which haven't gotten updates for ["
                            + SCAVENGE_OLD_STATS_SECONDS
                            + "] seconds: [" + stats.destinationName + "]");
                    currentStatsIterator.remove();
                }
            }

            // :: Notify listeners
            ActiveMqBrokerStatsEventImpl event = new ActiveMqBrokerStatsEventImpl(correlationId,
                    isFullUpdate, requestSameNode, originatingNodeId,
                    requestSameNode ? (System.nanoTime() - _nanosAtStart_RequestQuery) / 1_000_000d : -1);
            for (Consumer listener : _listeners) {
                listener.accept(event);
            }

            _countOfDestinationsReceivedSinceLastBatch = 0;
        }
        else {
            // -> No, we haven't got any messages - probably startup
            log.debug("We haven't gotten any stats messages - wait for first one.");
        }
    }

    private BrokerStatsDto mapMessageToBrokerStatsDto(MapMessage mm) throws JMSException {
        BrokerStatsDto dto = new BrokerStatsDto();
        mapMessageToCommonStatsDto(mm, dto);

        dto.stompSsl = (String) mm.getObject("stomp+ssl");
        dto.ssl = (String) mm.getObject("ssl");
        dto.stomp = (String) mm.getObject("stomp");
        dto.openwire = (String) mm.getObject("openwire");
        dto.vm = (String) mm.getObject("vm");

        dto.dataDirectory = (String) mm.getObject("dataDirectory");

        dto.tempUsage = (long) mm.getObject("tempUsage");
        dto.tempLimit = (long) mm.getObject("tempLimit");
        dto.tempPercentUsage = (int) mm.getObject("tempPercentUsage");

        dto.storeUsage = (long) mm.getObject("storeUsage");
        dto.storePercentUsage = (int) mm.getObject("storePercentUsage");
        dto.storeLimit = (long) mm.getObject("storeLimit");

        return dto;
    }

    private DestinationStatsDto mapMessageToDestinationStatsDto(MapMessage mm) throws JMSException {
        DestinationStatsDto dto = new DestinationStatsDto();
        mapMessageToCommonStatsDto(mm, dto);

        dto.destinationName = (String) mm.getObject("destinationName");
        dto.firstMessageTimestamp = getTimestampFromMapMessage(mm, "firstMessageTimestamp");

        return dto;
    }

    private Optional getTimestampFromMapMessage(MapMessage mm, String key) throws JMSException {
        long millis = mm.getLong(key);
        return millis != 0 ? Optional.of(Instant.ofEpochMilli(millis)) : Optional.empty();
    }

    private void mapMessageToCommonStatsDto(MapMessage mm, CommonStatsDto dto) throws JMSException {
        dto.statsReceived = Instant.now(_clock);

        dto.brokerId = (String) mm.getObject("brokerId");
        dto.brokerName = (String) mm.getObject("brokerName");
        dto.brokerTime = Instant.ofEpochMilli(mm.getJMSTimestamp());

        dto.size = (long) mm.getObject("size");
        dto.enqueueCount = (long) mm.getObject("enqueueCount");
        dto.dequeueCount = (long) mm.getObject("dequeueCount");
        dto.expiredCount = (long) mm.getObject("expiredCount");
        dto.dispatchCount = (long) mm.getObject("dispatchCount");
        dto.inflightCount = (long) mm.getObject("inflightCount");

        dto.producerCount = (long) mm.getObject("producerCount");
        dto.consumerCount = (long) mm.getObject("consumerCount");

        dto.minEnqueueTime = (double) mm.getObject("minEnqueueTime");
        dto.averageEnqueueTime = (double) mm.getObject("averageEnqueueTime");
        dto.maxEnqueueTime = (double) mm.getObject("maxEnqueueTime");

        dto.memoryUsage = (long) mm.getObject("memoryUsage");
        dto.memoryLimit = (long) mm.getObject("memoryLimit");
        dto.memoryPercentUsage = (int) mm.getObject("memoryPercentUsage");

        dto.averageMessageSize = (long) mm.getObject("averageMessageSize");

        dto.messagesCached = (long) mm.getObject("messagesCached");
    }

    private static class UnexpectedNullMessageReceivedException extends Exception {
        public UnexpectedNullMessageReceivedException(String message) {
            super(message);
        }
    }

    private static void chill(long millis) {
        log.debug("Chilling [" + millis + "] ms.");
        try {
            Thread.sleep(millis);
        }
        catch (InterruptedException e) {
            log.info("Got interrupted while chill-waiting [" + millis + "].");
        }
    }
}




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