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From tpavelka <tomas.pave...@ca.com>
Subject NPE when using a file based cursor with durable topic subscriptions
Date Wed, 01 Nov 2017 11:58:37 GMT
I am using a file based cursor with durable topic subscriptions because in my
tests the broker would run out of memory when dealing with large numbers of
messages without an active consumer.
I have run into a NullPointerException when the messages meant for the topic
with an active durable subscription expire. Here is part of the stack trace:

java.lang.NullPointerException: null
	at org.apache.activemq.broker.region.Topic.acknowledge(Topic.java:586)
[activemq-broker-5.15.2.jar:5.15.2]
	at org.apache.activemq.broker.region.Topic.messageExpired(Topic.java:810)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.cursors.FilePendingMessageCursor.discardExpiredMessage(FilePendingMessageCursor.java:489)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.cursors.FilePendingMessageCursor.tryAddMessageLast(FilePendingMessageCursor.java:247)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.cursors.AbstractPendingMessageCursor.addMessageLast(AbstractPendingMessageCursor.java:93)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.PrefetchSubscription.add(PrefetchSubscription.java:157)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.DurableTopicSubscription.add(DurableTopicSubscription.java:279)
[activemq-broker-5.15.2.jar:5.15.2]
	at org.apache.activemq.broker.region.Topic$2.recoverMessage(Topic.java:314)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.store.kahadb.KahaDBStore$KahaDBTopicMessageStore$6.execute(KahaDBStore.java:1012)
[activemq-kahadb-store-5.15.2.jar:5.15.2]
	at
org.apache.activemq.store.kahadb.disk.page.Transaction.execute(Transaction.java:779)
[activemq-kahadb-store-5.15.2.jar:5.15.2]
	at
org.apache.activemq.store.kahadb.KahaDBStore$KahaDBTopicMessageStore.recoverSubscription(KahaDBStore.java:999)
[activemq-kahadb-store-5.15.2.jar:5.15.2]
	at
org.apache.activemq.store.ProxyTopicMessageStore.recoverSubscription(ProxyTopicMessageStore.java:108)
[activemq-broker-5.15.2.jar:5.15.2]
	at org.apache.activemq.broker.region.Topic.activate(Topic.java:307)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.DurableTopicSubscription.add(DurableTopicSubscription.java:123)
[activemq-broker-5.15.2.jar:5.15.2]
	at org.apache.activemq.broker.region.Topic.addSubscription(Topic.java:164)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.TopicRegion.addSubscriptionsForDestination(TopicRegion.java:287)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.AbstractRegion.addDestination(AbstractRegion.java:162)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.RegionBroker.addDestination(RegionBroker.java:339)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.BrokerFilter.addDestination(BrokerFilter.java:174)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.advisory.AdvisoryBroker.addDestination(AdvisoryBroker.java:239)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.BrokerFilter.addDestination(BrokerFilter.java:174)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.BrokerFilter.addDestination(BrokerFilter.java:174)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.BrokerFilter.addDestination(BrokerFilter.java:174)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.AbstractRegion.start(AbstractRegion.java:104)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.region.RegionBroker.start(RegionBroker.java:200)
[activemq-broker-5.15.2.jar:5.15.2]
	at org.apache.activemq.broker.BrokerFilter.start(BrokerFilter.java:189)
[activemq-broker-5.15.2.jar:5.15.2]
	at org.apache.activemq.broker.BrokerFilter.start(BrokerFilter.java:189)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.TransactionBroker.start(TransactionBroker.java:119)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.BrokerService$6.start(BrokerService.java:2370)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.BrokerService.doStartBroker(BrokerService.java:747)
[activemq-broker-5.15.2.jar:5.15.2]
	at
org.apache.activemq.broker.BrokerService.startBroker(BrokerService.java:733)
[activemq-broker-5.15.2.jar:5.15.2]
	at org.apache.activemq.broker.BrokerService.start(BrokerService.java:636)
[activemq-broker-5.15.2.jar:5.15.2]

I looked at the code and it seems to me that this is caused by the method
org.apache.activemq.broker.region.cursors.FilePendingMessageCursor#discardExpiredMessage:

   private void discardExpiredMessage(MessageReference reference) {
        LOG.debug("Discarding expired message {}", reference);
        if (reference.isExpired() && broker.isExpired(reference)) {
            ConnectionContext context = new ConnectionContext(new
NonCachedMessageEvaluationContext());
            context.setBroker(broker);
           
((Destination)reference.getRegionDestination()).messageExpired(context,
null, new IndirectMessageReference(reference.getMessage()));
        }
    }

There the subscription passed to Destination#messageExpired is set to null.
If the destination is a topic, then later in
org.apache.activemq.broker.region.Topic#acknowledge:

    @Override
    public void acknowledge(ConnectionContext context, Subscription sub,
final MessageAck ack,
            final MessageReference node) throws IOException {
        if (topicStore != null && node.isPersistent()) {
            DurableTopicSubscription dsub = (DurableTopicSubscription) sub;
            SubscriptionKey key = dsub.getSubscriptionKey();
            topicStore.acknowledge(context, key.getClientId(),
key.getSubscriptionName(), node.getMessageId(),
                    convertToNonRangedAck(ack, node));
        }
        messageConsumed(context, node);
    }

The code dsub.getSubscriptionKey() throws an NPE.

Is this a bug or am I using the wrong type of cursor?

Thanks,
Tomas



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