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https://issues.apache.org/jira/browse/AMQNET-727?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Krzysztof Porębski resolved AMQNET-727.
---------------------------------------
Resolution: Fixed
> Thread sync error with MessageConsumer.pendingAck
> -------------------------------------------------
>
> Key: AMQNET-727
> URL: https://issues.apache.org/jira/browse/AMQNET-727
> Project: ActiveMQ .Net
> Issue Type: Bug
> Components: OpenWire
> Affects Versions: 1.8.0
> Reporter: Andy DeMaurice
> Priority: Major
> Fix For: OpenWire-2.1.1
>
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> pendingAck is accessed by multiple threads; in most places where it is
> written, it is done along with accessing *deliveredMessages*, so it is
> written within a *lock(this.deliveredMessages)* block.
> However, this call stack shows where pendingAck gets assigned to a new
> MessageAck object, NOT within the lock... and it is subject to being
> overwritten by another thread (usually the other thread is in
> MessageConsumer.Acknowledge() :
>
> Apache.NMS.ActiveMQ.MessageConsumer.AckLater(Apache.NMS.ActiveMQ.Commands.MessageDispatch,
> Apache.NMS.ActiveMQ.AckType)
> Apache.NMS.ActiveMQ.MessageConsumer.AfterMessageIsConsumed(Apache.NMS.ActiveMQ.Commands.MessageDispatch,
> Boolean)
> Apache.NMS.ActiveMQ.MessageConsumer.Dispatch(Apache.NMS.ActiveMQ.Commands.MessageDispatch)
> Apache.NMS.ActiveMQ.SessionExecutor.Dispatch(Apache.NMS.ActiveMQ.Commands.MessageDispatch)
> Apache.NMS.ActiveMQ.SessionExecutor.Iterate()
> Apache.NMS.ActiveMQ.Threads.DedicatedTaskRunner.Run()
>
> The usual symptom I see is a NullReferenceException in this section of code
> within AckLater; because pendingAck has been set to null by another thread:
>
> if(oldPendingAck == null)
> {
> pendingAck.FirstMessageId = pendingAck.LastMessageId;
> }
> else if(oldPendingAck.AckType == pendingAck.AckType)
> {
> pendingAck.FirstMessageId = oldPendingAck.FirstMessageId;
> }
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